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{{Short description|Inflammation of the alveoli of the lungs}}
{{otheruses4|human pneumonia|pneumonia in animals|pneumonia (non-human)}}
{{cs1 config|name-list-style=vanc}}
{{Infobox Disease |
{{confuse|Pneumonitis}}
Name = Pneumonia |
{{Other uses}}
Image = |
{{pp-semi-indef}}
Caption = |
{{Good article}}
DiseasesDB = 10166 |
{{Use dmy dates|date=March 2023}}
ICD10 = {{ICD10|J|12||j|09}}, {{ICD10|J|13||j|09}}, {{ICD10|J|14||j|09}}, {{ICD10|J|15||j|09}}, {{ICD10|J|16||j|09}}, {{ICD10|J|17||j|09}}, {{ICD10|J|18||j|09}}, {{ICD10|P|23||p|20}} |
{{Infobox medical condition (new)
ICD9 = {{ICD9|480}}-{{ICD9|486}}, {{ICD9|770.0}} |
ICDO = | | name = Pneumonia
| image = Chest radiograph in influensa and H influenzae, posteroanterior, annotated.jpg
OMIM = |
MedlinePlus = | | alt =
| caption = ] of a pneumonia caused by ] and '']'', with patchy consolidations, mainly in the right upper lobe (arrow)
eMedicineSubj = search |
| pronounce = {{IPAc-en|nj|uː|ˈ|m|əʊ|n|i|ə}} {{respell|new|MOHN|ee-ə}}
eMedicineTopic = pneumonia |
MeshName = Pneumonia | | synonyms = Pneumonitis
| field = ], ]
MeshNumber = C08.381.677 |
| symptoms = Cough, ], chest pain, fever<ref name="NIH2">{{cite web |title=Pneumonia – Symptoms {{!}} NHLBI, NIH |url=https://www.nhlbi.nih.gov/health/pneumonia/symptoms |website=nhlbi.nih.gov |date=24 March 2022 |access-date=1 October 2022 |language=en}}</ref>
| duration = Few weeks<ref name=Behera2010/>
| onset =
| causes = Bacteria, virus, ]<ref name=RespText09/><ref name=Jeff2010/>
| risks = ], ], ], ], ], heart failure, history of smoking, very young age, older age<ref name="NIH2022">{{cite web |title=Pneumonia – Causes and Risk Factors {{!}} NHLBI, NIH |url=https://www.nhlbi.nih.gov/health/pneumonia/causes |website=nhlbi.nih.gov |date=24 March 2022 |access-date=1 October 2022 |language=en}}</ref><ref name=-BMJ2012>{{cite journal | vauthors = Caldeira D, Alarcão J, Vaz-Carneiro A, Costa J | title = Risk of pneumonia associated with use of angiotensin converting enzyme inhibitors and angiotensin receptor blockers: systematic review and meta-analysis | journal = BMJ | volume = 345 | issue = jul11 1 | pages = e4260 | date = July 2012 | pmid = 22786934 | pmc = 3394697 | doi = 10.1136/bmj.e4260 | quote = Susceptibility is higher among elderly people (≥65 years) }}</ref><ref name=CDC2020SCD/>
| diagnosis = Based on symptoms, ]<ref name=NIH2011Diag/>
| differential = ], ], ], ]<ref name=BMJ06/>
| prevention = ]s, ], not smoking<ref name=NIH2011Pre/>
| medication = ]s, ]s, ]<ref name=NIH2011Tx/><ref name=Lancet11/>
| treatment =
| frequency = 450 million (7%) per year<ref name=Lancet11/><ref name=CochraneTx13/>
| deaths = Four million per year<ref name=Lancet11/><ref name=CochraneTx13/>
}} }}


'''Pneumonia''' is an ] condition of the ] primarily affecting the small air sacs known as ].<ref name=RespText09>{{cite book| veditors = McLuckie A |title=Respiratory disease and its management|year=2009|publisher=Springer|location=New York|isbn=978-1-84882-094-4|page=51}}</ref><ref name=AcuteCare09>{{cite book | last = Leach | first = Richard E. |title=Acute and Critical Care Medicine at a Glance |edition=2nd |publisher=Wiley-Blackwell |year=2009 |isbn=978-1-4051-6139-8 |url=https://books.google.com/books?id=7u_wu5VCsVQC&pg=PT168 }}</ref> Symptoms typically include some combination of ], ], fever, and ].<ref name=Ash2007>{{cite book | last1 = Ashby | first1 = Bonnie | last2 = Turkington | first2 = Carol | title = The encyclopedia of infectious diseases |edition=3rd |publisher=Facts on File |location=New York |year=2007 |page=242 |isbn=978-0-8160-6397-0 |url=https://books.google.com/books?id=4Xlyaipv3dIC&pg=PA242 |access-date=21 April 2011 }}</ref> The severity of the condition is variable.<ref name=Ash2007/>
'''Pneumonia''' is an illness of the ]s and ] in which the ] (microscopic air-filled sacs of the lung responsible for absorbing ] from the ]) become inflamed and flooded with fluid. Pneumonia can result from a variety of causes, including ] with ], ]es, ], or ]s. Pneumonia may also occur from chemical or physical injury to the lungs.


Pneumonia is usually caused by infection with viruses or bacteria, and less commonly by other ]s.{{efn|The term ''pneumonia'' is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by ]s, chemical burns or certain ]),<ref name="RespText09" /><ref name="Jeff2010">{{cite book | first = Jeffrey C. | last = Pommerville |title=Alcamo's Fundamentals of Microbiology |edition=9th |publisher=Jones & Bartlett |location=Sudbury, MA |year=2010 |page=323 |isbn=978-0-7637-6258-2 |url=https://books.google.com/books?id=RJNQwQB8IxIC&pg=PA323 }}</ref> but this inflammation is more accurately referred to as ].<ref name="isbn0-7234-3200-7">{{cite book | vauthors = Lowe JF, Stevens A | title = Pathology |edition=2nd |publisher=Mosby |location=St. Louis |year=2000 |page=197 |isbn=978-0-7234-3200-5 |url=https://books.google.com/books?id=AfVxLi4QTZQC&pg=PA197}}</ref><ref name="Bowden2010">{{cite book|editor-last1=Bowden|editor-first1=Raleigh A.|editor-last2=Ljungman|editor-first2=Per|editor-last3=Snydman|editor-first3=David R. |title=Transplant infections|year=2010|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|location=Philadelphia|isbn=978-1-58255-820-2}}</ref>}} Identifying the responsible pathogen can be difficult. Diagnosis is often based on symptoms and ].<ref name=NIH2011Diag/> ]s, blood tests, and ] of the ] may help confirm the diagnosis.<ref name=NIH2011Diag>{{cite web|title=How Is Pneumonia Diagnosed?|url=http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/diagnosis|website=NHLBI|access-date=3 March 2016|date=1 March 2011|url-status=live|archive-url=https://web.archive.org/web/20160307133513/http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/diagnosis|archive-date=7 March 2016}}</ref> The disease may be classified by where it was acquired, such as community- or hospital-acquired or healthcare-associated pneumonia.<ref>{{cite web|title=Types of Pneumonia|url=http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/types|website=NHLBI|access-date=2 March 2016|date=1 March 2011|archive-url=https://web.archive.org/web/20160205213840/http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/types|archive-date=5 February 2016}}</ref>
Typical symptoms associated with pneumonia include ], ], ], and ]. ] tools include ]s and examination of the ]. Treatment depends on the cause of pneumonia; bacterial pneumonia is treated with ]s.
{{Pneumonia}}
Pneumonia is a common illness which occurs in all age groups, and is a leading cause of ] among the elderly and people who are chronically and terminally ill. ]s to prevent certain types of pneumonia are available. The ] depends on the type of pneumonia, the appropriate treatment, any complications, and the person's underlying ].


Risk factors for pneumonia include ], ] (COPD), ], ], ], ], a history of smoking, a poor ability to cough (such as following a stroke), and ].<ref name="NIH2022"/><ref name=CDC2020SCD>{{cite web |title=Complications and Treatments of Sickle Cell Disease {{!}} CDC |url=https://www.cdc.sgov/ncbddd/sicklecell/treatments.html |website=Centers for Disease Control and Prevention |access-date=6 May 2020 |language=en-us |date=12 June 2019}}</ref>
==Symptoms==
] with fluid, keeping oxygen from reaching the bloodstream. The alveolus on the left is normal, while the alveolus on the right is full of fluid from pneumonia.]]
People with infectious pneumonia often have a cough that produces greenish or yellow ] and a high ] that may be accompanied by ]. ] is also common, as is pleuritic ], a sharp or stabbing pain, either felt or worse during deep breaths or coughs. People with pneumonia may ], experience ]s, or develop ] and clammy skin. Other symptoms may include ], fatigue, ], ], ], mood swings, and ] or ]. Less common forms of pneumonia can cause a variety of other symptoms. For instance, pneumonia caused by '']'' may cause abdominal pain and ], while pneumonia caused by ] or ] may cause only ] and ]. In elderly people the manifestations of pneumonia may not be typical. Instead, they may develop new or worsening confusion or may experience unsteadiness leading to falls. Infants with pneumonia may have many of the symptoms above, but in many cases, they are simply sleepy or have decreased appetite.


]s to prevent certain types of pneumonia (such as those caused by '']'' bacteria, ], or ]) are available.<ref name=NIH2011Pre/> Other methods of prevention include ] to prevent infection, prompt treatment of worsening respiratory symptoms, and not smoking.<ref name=NIH2011Pre>{{cite web|title=How Can Pneumonia Be Prevented?|url=http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/prevention|website=NHLBI|access-date=3 March 2016|date=1 March 2011|url-status=live|archive-url=https://web.archive.org/web/20160307133901/http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/prevention|archive-date=7 March 2016}}</ref><ref name="y782">{{cite book | last=Lim | first=Wei Shen | title=Encyclopedia of Respiratory Medicine | chapter=Pneumonia—Overview | publisher=Elsevier | date=2022 | isbn=978-0-08-102724-0 | pmc=7241411 | doi=10.1016/b978-0-12-801238-3.11636-8 | page=185–197}}</ref>
==Diagnosis==
To diagnose pneumonia, health care providers rely on a patient's ] and findings from ]. Information from a ], ]s, and sputum ]s may also be helpful. The chest X-ray is typically used for diagnosis in hospitals and some clinics with X-ray facilities. However, in a community setting (]), pneumonia is usually diagnosed based on symptoms and physical examination alone. Diagnosing pneumonia can be difficult in some people, especially those who have other illnesses. Occasionally a chest ] or other tests may be needed to distinguish pneumonia from other illnesses.


Treatment depends on the underlying cause.<ref name=NIH2011>{{cite web|title=What Is Pneumonia?|url=http://www.nhlbi.nih.gov/health/health-topics/topics/pnu|website=NHLBI|access-date=2 March 2016|date=1 March 2011|url-status=live|archive-url=https://web.archive.org/web/20160229143108/https://www.nhlbi.nih.gov/health/health-topics/topics/pnu/|archive-date=29 February 2016}}</ref> Pneumonia believed to be due to bacteria is treated with ]s.<ref name=NIH2011Tx>{{cite web|title=How Is Pneumonia Treated?|url=http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/treatment|website=NHLBI|access-date=3 March 2016|date=1 March 2011|url-status=live|archive-url=https://web.archive.org/web/20160306030735/http://www.nhlbi.nih.gov/health/health-topics/topics/pnu/treatment|archive-date=6 March 2016}}</ref> If the pneumonia is severe, the affected person is generally hospitalized.<ref name=NIH2011/> ] may be used if oxygen levels are low.<ref name=NIH2011Tx/>
===Physical examination===
Individuals with symptoms of pneumonia need medical evaluation. ] by a health care provider may reveal ] or sometimes ], an ], ], a ], or a low ], which is the amount of oxygen in the blood as indicated by either ] or ]. People who are struggling to breathe, confused, or who have ] (blue-tinged skin) require immediate attention.
[[Image:Pneumonia_x-ray.jpg|thumb|left|170px|'''Pneumonia as seen on chest x-ray.'''
''A'': Normal chest x-ray. ''B'': Abnormal chest x-ray with shadowing from pneumonia in the right lung (left side of image).]]
Listening to the lungs with a ] (]) can reveal several things. A lack of normal breath sounds, the presence of crackling sounds (]), or increased loudness of whispered speech (whispered pectoriloquy) can identify areas of the lung that are stiff and full of fluid, called "consolidation." The examiner may also feel the way the chest expands (]) and tap the chest wall (]) to further localize consolidation. The examiner may also palpate for increased vibration of the chest when speaking (tactile fremitus).<ref name=metlay>Metlay JP, Kapoor WN, Fine MJ. Does this patient have community-acquired pneumonia? Diagnosing pneumonia by history and physical examination. ''JAMA'' 1997; 278:1440. PMID 9356004</ref>


Each year, pneumonia affects about 450&nbsp;million people globally (7% of the population) and results in about 4 million deaths.<ref name=Lancet11>{{cite journal | vauthors = Ruuskanen O, Lahti E, Jennings LC, Murdoch DR | title = Viral pneumonia | journal = Lancet | volume = 377 | issue = 9773 | pages = 1264–75 | date = April 2011 | pmid = 21435708 | pmc = 7138033 | doi = 10.1016/S0140-6736(10)61459-6 }}</ref><ref name=CochraneTx13>{{cite journal | vauthors = Lodha R, Kabra SK, Pandey RM | title = Antibiotics for community-acquired pneumonia in children | journal = The Cochrane Database of Systematic Reviews | volume = 6 | issue = 6 | pages = CD004874 | date = June 2013 | pmid = 23733365 | pmc = 7017636 | doi = 10.1002/14651858.CD004874.pub4 }}</ref> With the introduction of antibiotics and vaccines in the 20th century, survival has greatly improved.<ref name=Lancet11/> Nevertheless, pneumonia remains a ] in developing countries, and also among the very old, the very young, and the ] ill.<ref name=Lancet11/><ref>{{cite book|last=George|first=Ronald B.|title=Chest medicine: essentials of pulmonary and critical care medicine|year=2005|publisher=Lippincott Williams & Wilkins |location=Philadelphia|isbn=978-0-7817-5273-2|page=353|url=https://books.google.com/books?id=ZzlX2zJMbdgC&pg=PA353|edition=5th}}</ref> Pneumonia often shortens the period of suffering among those already close to death and has thus been called "the old man's friend".<ref name=EBMED05>{{cite journal|last=Eddy|first=Orin|title=Community-Acquired Pneumonia: From Common Pathogens To Emerging Resistance|journal=Emergency Medicine Practice|date=Dec 2005|volume=7|issue=12|url=https://www.ebmedicine.net/topics.php?paction=showTopic&topic_id=118}}</ref>
===Chest X-rays, sputum cultures, and other tests===
])]]
An important test for detecting pneumonia in unclear situations is a chest ]. Chest x-rays can reveal areas of ] (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray. In some cases, chest CT (]) can reveal pneumonia that is not seen on chest x-ray. X-rays can be misleading, because other problems, like lung scarring and ], can mimic pneumonia on x-ray.<ref name=syrjala>Syrjala H, Broas M, Suramo I, et al. ''High resolution computed tomography for the diagnosis of community-acquired pneumonia.'' Clin Infect Dis 1998; 27:358-363 PMID 9709887</ref> Chest x-rays are also used to evaluate for complications of pneumonia. (''].'')
{{TOC limit}}


==Signs and symptoms==
If an individual is not getting better with antibiotics, or if the health care provider has concerns about the diagnosis, a ] of the person's ] may be requested. Sputum cultures generally take at least two to three days, so they are mainly used to confirm that the infection is sensitive to an antibiotic that has already been started. A blood sample may similarly be cultured to look for infection in the blood (]). Any bacteria identified are then tested to see which antibiotics will be most effective.
]
People with infectious pneumonia often have a ], fever accompanied by ], ], sharp or stabbing ] during deep breaths, and an increased ].<ref name=BMJ06/> In elderly people, confusion may be the most prominent sign.<ref name=BMJ06>{{cite journal | vauthors = Hoare Z, Lim WS | title = Pneumonia: update on diagnosis and management | journal = BMJ | volume = 332 | issue = 7549 | pages = 1077–79 | date = May 2006 | pmid = 16675815 | pmc = 1458569 | doi = 10.1136/bmj.332.7549.1077 }}</ref>


The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing.<ref name=Develop11/> Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease, ] or in the elderly. In addition, a cough is frequently absent in children less than 2 months old.<ref name=Develop11/> More severe signs and symptoms in children may include ], unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a ].<ref name=Develop11/><ref name=Clinic2011/>
A ] may show a ], indicating the presence of an infection or inflammation. In some people with ], the white blood cell count may appear deceptively normal. Blood tests may be used to evaluate ] function (important when prescribing certain antibiotics) or to look for ]. Low blood sodium in pneumonia is thought to be due to extra ] produced when the lungs are diseased (]). Specific blood ] tests for other bacteria (''Mycoplasma'', ''Legionella'' and ''Chlamydophila'') and a ] test for ''Legionella'' ] are available. Respiratory secretions can also be tested for the presence of viruses such as ], ], and ].


Bacterial and viral cases of pneumonia usually result in similar symptoms.<ref name=WHOPrevent2012/> Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by '']'' may occur with abdominal pain, ], or confusion.<ref>{{cite journal |vauthors=Darby J, Buising K |date=October 2008 |title=Could it be Legionella? |journal=Australian Family Physician |volume=37 |issue=10 |pages=812–15 |pmid=19002299}}</ref> Pneumonia caused by '']'' is associated with rusty colored sputum.<ref>{{cite journal |vauthors=Ortqvist A, Hedlund J, Kalin M |date=December 2005 |title=Streptococcus pneumoniae: epidemiology, risk factors, and clinical features |journal=Seminars in Respiratory and Critical Care Medicine |volume=26 |issue=6 |pages=563–74 |doi=10.1055/s-2005-925523 |pmid=16388428|s2cid=260320485 }}</ref> Pneumonia caused by '']'' may have bloody sputum often described as "currant jelly".<ref name=Tint10>{{cite book | last = Tintinalli | first = Judith E. |title=Emergency Medicine: A Comprehensive Study Guide (Emergency Medicine (Tintinalli))|publisher=McGraw-Hill Companies |location=New York|year=2010|page=480 |isbn=978-0-07-148480-0 }}</ref> Bloody sputum (known as ]) may also occur with ], Gram-negative pneumonia, ]es and more commonly ].<ref name=Clinic2011/> Pneumonia caused by '']'' may occur in association with ], ], or a ].<ref name=Clinic2011/> Viral pneumonia presents more commonly with ] than bacterial pneumonia.<ref name=WHOPrevent2012/> Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause.<ref name=M32/> However, evidence has not supported this distinction, therefore it is no longer emphasized.<ref name=M32/>
===Combining findings===
{|class="wikitable" align="right" style="margin-left:0.4em;"
One study created a prediction rule that found the five following signs best predicted infiltrates on the chest radiograph of 1134 patients presenting to an emergency room<ref name="pmid2221647">{{cite journal |author=Heckerling PS, Tape TG, Wigton RS, ''et al'' |title=Clinical prediction rule for pulmonary infiltrates |journal=Ann. Intern. Med. |volume=113 |issue=9 |pages=664-70 |year=1990 |pmid=2221647 |doi=}}</ref>:
!colspan=2| Symptoms frequency<ref name=Tint10/>
*Temperature > 37.8 degrees C
|-
*Pulse > 100 beats/min
! Symptom !! Frequency
*Crackles
|-
*Decreased breath sounds
| Cough || style="text-align: center;"| 79–91%
*''Absence'' of asthma
|-
| Fatigue || style="text-align: center;"| 90%
|-
| Fever || style="text-align: center;"| 71–75%
|-
| Shortness of breath || style="text-align: center;"| 67–75%
|-
| Sputum || style="text-align: center;"| 60–65%
|-
| Chest pain || style="text-align: center;"| 39–49%
|-
|}


==Cause==
The probability of an infiltrate in two separate validations was based on the number of findings:
]'', a common cause of pneumonia, imaged by an ]]]
*5 findings - 84% to 91% probability
Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and ]. Although more than 100 strains of infectious agents have been identified, only a few are responsible for the majority of cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults.<ref name=Lancet11/> A causative agent may not be isolated in about half of cases despite careful testing.<ref name=EBMED05/> In an active population-based surveillance for community-acquired pneumonia requiring hospitalization in five hospitals in Chicago and Nashville from January 2010 through June 2012, 2259 patients were identified who had radiographic evidence of pneumonia and specimens that could be tested for the responsible pathogen.<ref name="EPIC2015">{{cite journal | vauthors = Jain S, Self WH, Wunderink RG, Fakhran S, Balk R, Bramley AM, Reed C, Grijalva CG, Anderson EJ, Courtney DM, Chappell JD, Qi C, Hart EM, Carroll F, Trabue C, Donnelly HK, Williams DJ, Zhu Y, Arnold SR, Ampofo K, Waterer GW, Levine M, Lindstrom S, Winchell JM, Katz JM, Erdman D, Schneider E, Hicks LA, McCullers JA, Pavia AT, Edwards KM, Finelli L | title = Community-Acquired Pneumonia Requiring Hospitalization among U.S. Adults | journal = The New England Journal of Medicine | volume = 373 | issue = 5 | pages = 415–27 | date = July 2015 | pmid = 26172429 | pmc = 4728150 | doi = 10.1056/NEJMoa1500245 }}</ref> Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria.<ref name="EPIC2015"/> Specifically, 23% had one or more viruses, 11% had one or more bacteria, 3% had both bacterial and viral pathogens, and 1% had a fungal or mycobacterial infection. "The most common pathogens were ] (in 9% of patients), influenza virus (in 6%), and ''Streptococcus pneumoniae'' (in 5%)."<ref name="EPIC2015"/>
*4 findings - 58% to 85%
*3 findings - 35% to 51%
*2 findings - 14% to 24%
*1 findings - 5% to 9%
*0 findings - 2% to 3%


The term ''pneumonia'' is sometimes more broadly applied to any condition resulting in ] of the lungs (caused for example by ]s, chemical burns or drug reactions); however, this inflammation is more accurately referred to as ].<ref name="isbn0-7234-3200-7"/><ref name=Bowden2010/>
A subsequent study<ref name="pmid1952308">{{cite journal |author=Emerman CL, Dawson N, Speroff T, ''et al'' |title=Comparison of physician judgment and decision aids for ordering chest radiographs for pneumonia in outpatients |journal=Annals of emergency medicine |volume=20 |issue=11 |pages=1215-9 |year=1991 |pmid=1952308 |doi=}}</ref> comparing four prediction rules to physician judgment found that two rules, the one above<ref name="pmid2221647"/> and also<ref name="pmid2745948">{{cite journal |author=Gennis P, Gallagher J, Falvo C, Baker S, Than W |title=Clinical criteria for the detection of pneumonia in adults: guidelines for ordering chest roentgenograms in the emergency department |journal=The Journal of emergency medicine |volume=7 |issue=3 |pages=263-8 |year=1989 |pmid=2745948 |doi=}}</ref>, were more accurate than physician judgment because of the increased specificity of the prediction rules.


Factors that predispose to pneumonia include smoking, ], alcoholism, ], ] (SCD), ], ], ], and ].<ref name=Clinic2011/><ref>{{cite book|editor-last=Marrie|editor-first=Thomas J. |title=Community-acquired pneumonia|date=2002|publisher=Kluwer Academic Publishers|location=New York|isbn=978-0-306-46834-6|page=20|url=https://books.google.com/books?id=Yc0RBwAAQBAJ&pg=PA20}}</ref><ref name=CDC2020SCD/> Additional risks in children include not being ], exposure to cigarette smoke and other air pollution, malnutrition, and poverty.<ref>{{cite journal | vauthors = Nguyen TK, Tran TH, Roberts CL, Fox GJ, Graham SM, Marais BJ | title = Risk factors for child pneumonia – focus on the Western Pacific Region | journal = Paediatric Respiratory Reviews | volume = 21 | pages = 95–101 | date = January 2017 | pmid = 27515732 | doi = 10.1016/j.prrv.2016.07.002 }}</ref> The use of acid-suppressing medications – such as ] or ] – is associated with an increased risk of pneumonia.<ref>{{cite journal | vauthors = Eom CS, Jeon CY, Lim JW, Cho EG, Park SM, Lee KS | title = Use of acid-suppressive drugs and risk of pneumonia: a systematic review and meta-analysis | journal = CMAJ | volume = 183 | issue = 3 | pages = 310–19 | date = February 2011 | pmid = 21173070 | pmc = 3042441 | doi = 10.1503/cmaj.092129 }}</ref> Approximately 10% of people who require ] develop ],<ref name="Ar2016">{{cite journal | vauthors = Arthur LE, Kizor RS, Selim AG, van Driel ML, Seoane L | title = Antibiotics for ventilator-associated pneumonia | journal = The Cochrane Database of Systematic Reviews | volume = 2016 | pages = CD004267 | date = October 2016 | issue = 10 | pmid = 27763732 | pmc = 6461148 | doi = 10.1002/14651858.CD004267.pub4 }}</ref> and people with a ] have an increased risk of developing ].<ref>{{cite journal | vauthors = Alkhawaja S, Martin C, Butler RJ, Gwadry-Sridhar F | title = Post-pyloric versus gastric tube feeding for preventing pneumonia and improving nutritional outcomes in critically ill adults | journal = The Cochrane Database of Systematic Reviews | issue = 8 | pages = CD008875 | date = August 2015 | volume = 2018 | pmid = 26241698 | pmc = 6516803 | doi = 10.1002/14651858.CD008875.pub2 }}</ref> Moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia.<ref>{{cite web |date=5 March 2013 |title=Interprofessional Task force Uses a collaborative approach for internal feeding tube management |url=https://issuu.com/umms/docs/nv-winter_2013 |access-date=16 January 2023 |website=News and Views |page=10 |language=en}}</ref><ref>{{cite journal |date=17 November 2016 |title=ASPEN Safe Practices for Enteral Nutrition Therapy |url=https://eclass.hua.gr/modules/document/file.php/DIET159/JPEN%20J%20Parenter%20Enteral%20Nutr-2016-Boullata-0148607116673053.pdf |journal=Journal of Parenteral and Enteral Nutrition |volume=XX |issue=X |access-date=16 January 2023 |archive-date=16 January 2023 |archive-url=https://web.archive.org/web/20230116100215/https://eclass.hua.gr/modules/document/file.php/DIET159/JPEN%20J%20Parenter%20Enteral%20Nutr-2016-Boullata-0148607116673053.pdf }}</ref> As with ]'s feeding tube placement system, the CORTRAK* 2 EAS, which was recalled in May 2022 by the ] due to adverse events reported, including pneumonia, caused a total of 60 injuries and 23 patient deaths, as communicated by the FDA.<ref>{{cite journal |date=21 March 2022 |title=Urgent: Field Correction Cortrak* 2 Enteral Access System (EAS) |url=https://static.foxnews.com/foxnews.com/content/uploads/2022/04/Avanos_CORTRAK2_Field_Correction_Letter.pdf |journal=Avanos |pages=1–2}}</ref><ref>{{cite web |last=Park |first=Andrea |date=16 May 2022 |title=Avanos Medical faces Class I recall for feeding tube system linked to 23 deaths since 2015 |url=https://www.fiercebiotech.com/medtech/avanos-medical-faces-class-i-recall-feeding-tube-system-linked-23-deaths-2015 |access-date=16 January 2023 |website=Fierce Biotech |language=en}}</ref><ref>{{cite journal |last=Health |first=Center for Devices and Radiological |date=16 May 2022 |title=Avanos Medical Recalls Cortrak*2 Enteral Access System for Risk of Misplaced Enteral Tubes Could Cause Patient Harm |url=https://www.fda.gov/medical-devices/medical-device-recalls/avanos-medical-recalls-cortrak2-enteral-access-system-risk-misplaced-enteral-tubes-could-cause |journal=FDA |language=en}}</ref> For people with certain variants of the ], the risk of death is reduced in ] caused by pneumonia. However, for those with ] variants, the risk of getting ] is increased.<ref name="Elena 2015"/>
==Pathophysiology==

] that contain air. ''Lower panel'' shows a lung with pneumonia under a microscope. The alveoli are filled with inflammation and debris.]]
===Bacteria===
The symptoms of infectious pneumonia are caused by the invasion of the lungs by ]s and by the ]'s response to the infection. Although more than one hundred strains of microorganism can cause pneumonia, only a few of them are responsible for most cases. The most common causes of pneumonia are ]es and ]. Less common causes of infectious pneumonia include ] and ].
{{Main|Bacterial pneumonia}}
]
Bacteria are the most common cause of ] (CAP), with ''Streptococcus pneumoniae'' isolated in nearly 50% of cases.<ref name=Rad07/><ref name=EOP10>{{cite journal | vauthors = Anevlavis S, Bouros D | title = Community acquired bacterial pneumonia | journal = Expert Opinion on Pharmacotherapy | volume = 11 | issue = 3 | pages = 361–74 | date = February 2010 | pmid = 20085502 | doi = 10.1517/14656560903508770 | s2cid = 24376187 }}</ref> Other commonly isolated bacteria include '']'' in 20%, '']'' in 13%, and ''Mycoplasma pneumoniae'' in 3% of cases;<ref name=Rad07/> '']''; '']''; and '']''.<ref name=EBMED05/> A number of ] versions of the above infections are becoming more common, including drug-resistant ''Streptococcus pneumoniae'' (DRSP) and ] (MRSA).<ref name=Clinic2011/>

The spreading of organisms is facilitated by certain risk factors.<ref name=EBMED05/> Alcoholism is associated with ''Streptococcus pneumoniae'', ]s, and ''Mycobacterium tuberculosis''; smoking facilitates the effects of ''Streptococcus pneumoniae'', ''Haemophilus influenzae'', ''Moraxella catarrhalis'', and ''Legionella pneumophila''. Exposure to birds is associated with '']''; farm animals with '']''; aspiration of stomach contents with anaerobic organisms; and ] with '']'' and ''Staphylococcus aureus''.<ref name=EBMED05/> ''Streptococcus pneumoniae'' is more common in the winter,<ref name=EBMED05/> and it should be suspected in persons aspirating a large number of anaerobic organisms.<ref name=Clinic2011/>


===Viruses=== ===Viruses===
{{main|viral pneumonia}} {{Main|Viral pneumonia}}
]]]
Viruses must invade cells in order to reproduce. Typically, a virus reaches the lungs when airborne droplets are inhaled through the ] and ]. Once in the lungs, the virus invades the cells lining the airways and alveoli. This invasion often leads to cell death, either when the virus directly kills the cells, or through a type of cell self-destruction called ]. When the immune system responds to the viral infection, even more lung damage occurs. ]s, mainly ]s, activate a variety of chemical ]s which allow fluid to leak into the alveoli. This combination of cell destruction and fluid-filled alveoli interrupts the normal transportation of oxygen into the bloodstream.
In adults, viruses account for about one third of pneumonia cases,<ref name=Lancet11/> and in children for about 15% of them.<ref name=M31/> Commonly implicated agents include ]es, ]es, ], ] (RSV), ], and ].<ref name=Lancet11/><ref name=Viral09/> ] rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns.<ref name=Text2010>{{cite book|vauthors=Behera D|title=Textbook of pulmonary medicine|year=2010|publisher=Jaypee Brothers Medical Pub.|location=New Delhi|isbn=978-81-8448-749-7|pages=391–94|url=https://books.google.com/books?id=0TbJjd9eTp0C&pg=PA391|edition=2nd}}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> After ] or in otherwise ] persons, there are high rates of ] pneumonia.<ref name=M31/><ref name=Text2010/> Those with viral infections may be secondarily infected with the bacteria ''Streptococcus pneumoniae'', ''Staphylococcus aureus'', or ''Haemophilus influenzae'', particularly when other health problems are present.<ref name=Clinic2011/><ref name=M31/> Different viruses predominate at different times of the year; during ], for example, influenza may account for more than half of all viral cases.<ref name=M31/> Outbreaks of other viruses also occur occasionally, including ] and coronaviruses.<ref name=M31/> ] (SARS-CoV-2) can also result in pneumonia.<ref>{{cite journal | vauthors = Lai CC, Shih TP, Ko WC, Tang HJ, Hsueh PR | title = Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease-2019 (COVID-19): The epidemic and the challenges | journal = International Journal of Antimicrobial Agents | volume = 55 | issue = 3 | page = 105924 | date = March 2020 | pmid = 32081636 | pmc = 7127800 | doi = 10.1016/j.ijantimicag.2020.105924 | doi-access = free }}</ref>


===Fungi===
As well as damaging the lungs, many viruses affect other ]s and can thus disrupt many body functions. Viruses can also make the body more susceptible to bacterial infections; for which reason bacterial pneumonia often complicates viral pneumonia.
{{Main|Fungal pneumonia}}


Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, ]s, or other medical problems.<ref name=EBMED05/><ref name=Fungus2009>{{cite book|last1=Maskell|first1=Nick | last2 = Millar | first2 = Ann |title=Oxford Desk Reference: Respiratory Medicine |year=2009|publisher=Oxford University Press|location=Oxford | isbn = 978-0-19-923912-2 |page=196|url=https://books.google.com/books?id=MfEUkzQQ1BEC&pg=PA196}}</ref> It is most often caused by '']'', '']'', '']'', '']'' (], or PCP), and '']''. Histoplasmosis is most common in the ], and ] is most common in the Southwestern United States.<ref name=EBMED05/> The number of cases of fungal pneumonia has been increasing in the latter half of the 20th century due to increasing travel and rates of immunosuppression in the population.<ref name=Fungus2009/> For people infected with ], PCP is a common ].<ref name=Ewa2015>{{cite journal | vauthors = Ewald H, Raatz H, Boscacci R, Furrer H, Bucher HC, Briel M | title = Adjunctive corticosteroids for Pneumocystis jiroveci pneumonia in patients with HIV infection | journal = The Cochrane Database of Systematic Reviews | issue = 4 | pages = CD006150 | date = April 2015 | volume = 2015 | pmid = 25835432 | pmc = 6472444 | doi = 10.1002/14651858.CD006150.pub2 }}</ref>
Viral pneumonia is commonly caused by viruses such as ], ] (RSV), ], and ]. ] is a rare cause of pneumonia except in newborns. People with immune system problems are also at risk of pneumonia caused by ] (CMV).


===Bacteria=== ===Parasites===
{{main|bacterial pneumonia}} {{Main|Parasitic pneumonia}}
A variety of ]s can affect the lungs, including '']'', '']'', '']'', and '']''.<ref name=M37>Murray and Nadel (2010). Chapter 37.</ref> These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector.<ref name=M37/> Except for '']'', most parasites do not specifically affect the lungs but involve the lungs secondarily to other sites.<ref name=M37/> Some parasites, in particular those belonging to the ''Ascaris'' and ''Strongyloides'' genera, stimulate a strong ] reaction, which may result in ].<ref name=M37/> In other infections, such as malaria, lung involvement is due primarily to ]-induced ].<ref name=M37/> In the ], these infections are most common in people returning from travel or in immigrants.<ref name=M37/> Around the world, parasitic pneumonia is most common in the immunodeficient.<ref>{{cite journal | vauthors = Vijayan VK | title = Parasitic lung infections | journal = Current Opinion in Pulmonary Medicine | volume = 15 | issue = 3 | pages = 274–82 | date = May 2009 | pmid = 19276810 | doi = 10.1097/MCP.0b013e328326f3f8 | s2cid = 2631717 }}</ref>
Bacteria typically enter the lung when airborne droplets are inhaled, but they can also reach the lung through the bloodstream when there is an infection in another part of the body. Many bacteria live in parts of the ], such as the nose, mouth and sinuses, and can easily be inhaled into the alveoli. Once inside the alveoli, bacteria may invade the spaces between cells and between alveoli through connecting pores. This invasion triggers the ] to send ]s, which are a type of defensive white blood cell, to the lungs. The neutrophils ] and kill the offending organisms, and they also release ]s, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial and fungal pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transportation.
]''''', a common cause of pneumonia, photographed through an ].]]
Bacteria often travel from an infected lung into the bloodstream, causing serious or even fatal illness such as ], with low blood pressure and damage to multiple parts of the body including the ], ]s, and ]. Bacteria can also travel to the area between the lungs and the chest wall (the ]) causing a complication called an ].


===Noninfectious===
The most common causes of bacterial pneumonia are '']'', ] and "atypical" bacteria. The terms "Gram-positive" and "Gram-negative" refer to the bacteria's color (purple or red, respectively) when stained using a process called the ]. The term "atypical" is used because atypical bacteria commonly affect healthier people, cause generally less severe pneumonia, and respond to different antibiotics than other bacteria.
{{Main|Idiopathic interstitial pneumonia}}


Idiopathic interstitial pneumonia or noninfectious pneumonia<ref>{{cite book|editor-last=Root|editor-first=Richard K.|title=Clinical infectious diseases: a practical approach|year=1999|publisher=Oxford Univ. Press|location=New York |isbn=978-0-19-508103-9|page=833|url=https://books.google.com/books?id=zvCOpighJggC&pg=PA833}}</ref> is a class of ]s. They include ], ], ], ], ], ], and ].<ref>{{cite book| veditors = Costabel U |title=Diffuse parenchymal lung disease: 47 tables|year=2007|publisher=Karger|location=Basel|isbn=978-3-8055-8153-0|page=4|edition=}}</ref> ] is another rare cause due to ] entering the lung.<ref name=Had2010/> These lipids can either be inhaled or spread to the lungs from elsewhere in the body.<ref name="Had2010">{{cite journal |vauthors=Hadda V, Khilnani GC |date=December 2010 |title=Lipoid pneumonia: an overview |url=https://www.worldcat.org/title/262559133 |journal=Expert Review of Respiratory Medicine |volume=4 |issue=6 |pages=799–807 |doi=10.1586/ers.10.74 |oclc=262559133 |pmid=21128754 |s2cid=44309610}}</ref>
The types of Gram-positive bacteria that cause pneumonia can be found in the nose or mouth of many healthy people. '']'', often called "pneumococcus", is the most common bacterial cause of pneumonia in all age groups except newborn infants. Another important Gram-positive cause of pneumonia is '']''. Gram-negative bacteria cause pneumonia less frequently than gram-positive bacteria. Some of the gram-negative bacteria that cause pneumonia include '']'', '']'', '']'', '']'' and '']''. These bacteria often live in the ] and may enter the lungs if vomit is inhaled. "Atypical" bacteria which cause pneumonia include '']'', '']'', and '']''.


===Fungi=== ==Mechanisms==
] with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.]]
{{main|fungal pneumonia}}
Fungal pneumonia is uncommon, but it may occur in individuals with ] due to ], ]s, or other medical problems. The pathophysiology of pneumonia caused by fungi is similar to that of bacterial pneumonia. Fungal pneumonia is most often caused by '']'', '']'', '']'', and '']''. ] is most common in the ], and ] is most common in the ].


Pneumonia frequently starts as an ] that moves into the lower respiratory tract.<ref name=PedNA09>{{cite journal | vauthors = Ranganathan SC, Sonnappa S | title = Pneumonia and other respiratory infections | journal = Pediatric Clinics of North America | volume = 56 | issue = 1 | pages = 135–56, xi | date = February 2009 | pmid = 19135585 | pmc = 7111724 | doi = 10.1016/j.pcl.2008.10.005 }}</ref> It is a type of pneumonitis (lung inflammation).<ref>{{cite book|last1=Anderson|first1=Douglas M. |title=Dorland's illustrated medical dictionary|date=2000|publisher=Saunders|location=Philadelphia |isbn=978-0-7216-8261-7|page=|edition=29|url=https://archive.org/details/trent_0116404640520/page/1414}}</ref> The normal flora of the upper airway give protection by competing with pathogens for nutrients. In the lower airways, ], actions of ]s and ]s are important for protection. Micro] of contaminated secretions can infect the lower airways and cause pneumonia. The progress of pneumonia is determined by the virulence of the organism; the amount of organism required to start an infection; and the body's immune response against the infection.<ref name="Elena 2015"/>
===Parasites===
{{main|parasitic pneumonia}}
A variety of parasites can affect the lungs. These parasites typically enter the body through the skin or by being swallowed. Once inside the body, they travel to the lungs, usually through the blood. There, as in other types of pneumonia, a combination of cellular destruction and immune response causes disruption of oxygen transportation. One type of white blood cell, the ], responds vigorously to parasite infection. Eosinophils in the lungs can lead to ], thus complicating the underlying parasitic pneumonia. The most common parasites causing pneumonia are '']'', '']'', and '']''.


==Classification== ===Bacterial===
Most bacteria enter the lungs via small aspirations of organisms residing in the throat or nose.<ref name=Clinic2011/> Half of normal people have these small aspirations during sleep.<ref name=M32/> While the throat always contains bacteria, ] ones reside there only at certain times and under certain conditions.<ref name=M32/> A minority of types of bacteria such as '']'' and ''Legionella pneumophila'' reach the lungs via contaminated airborne droplets.<ref name=Clinic2011/> Bacteria can also spread via the blood.<ref name=WHOPrevent2012/> Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the ]s and ]s (defensive ]s) attempt to inactivate the bacteria.<ref>{{cite book|editor-last1=Hammer|editor-first1=Gary D.|editor-last2=McPhee|editor-first2=Stephen J. |title=Pathophysiology of disease: an introduction to clinical medicine|year=2010|publisher=McGraw-Hill Medical|location=New York|isbn=978-0-07-162167-0|page=Chapter 4|edition=6th}}</ref> The neutrophils also release cytokines, causing a general activation of the immune system.<ref name=Fein2006>{{cite book|last=Fein|first=Alan |title=Diagnosis and management of pneumonia and other respiratory infections|year=2006|publisher=Professional Communications|location=Caddo, OK|isbn=978-1-884735-63-9|pages=28–29|url=https://books.google.com/books?id=hKdcHK719qgC&pg=PA28|edition=2nd}}</ref> This leads to the fever, chills, and fatigue common in bacterial pneumonia.<ref name=Fein2006/> The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray.<ref>{{cite book|last=Kumar|first=Vinay|title=Robbins and Cotran pathologic basis of disease.|year=2010|publisher=Saunders/Elsevier|location=Philadelphia|isbn=978-1-4160-3121-5|page=Chapter 15|edition=8th}}</ref>
Pneumonias can be classified in several ways. Pathologists classified them according to the ] changes that were found in the lungs during ]. As more became known about the microorganisms causing pneumonia, a ] classification arose, and with the advent of ]s, a ] classification was developed. Another important classification system used for pneumonia is the combined clinical classification, which combines many factors, including age, risk factors for certain microorganisms, the presence of underlying lung disease and underlying systemic disease, and whether he or she has recently been hospitalized.


===Viral===
===Early classification schemes===
Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then touch their eyes or nose.<ref name=M31>Murray and Nadel (2010). Chapter 31.</ref> Other viral infections occur when contaminated airborne droplets are inhaled through the nose or mouth.<ref name=Clinic2011/> Once in the upper airway, the viruses may make their way into the lungs, where they invade the cells lining the airways, alveoli, or ].<ref name=M31/> Some viruses such as measles and herpes simplex may reach the lungs via the blood.<ref name=Gary2010>{{cite book|editor-last1=Fleisher|editor-first1=Gary R.|editor-last2=Ludwig|editor-first2=Stephen |title=Textbook of pediatric emergency medicine|year=2010|publisher=Wolters Kluwer/Lippincott Williams & Wilkins Health|location=Philadelphia|isbn=978-1-60547-159-4|page=914|url=https://books.google.com/books?id=a7CqcE1ZrFkC&pg=PA914|edition=6th}}</ref> The invasion of the lungs may lead to varying degrees of cell death.<ref name=M31/> When the immune system responds to the infection, even more lung damage may occur.<ref name=M31/> Primarily white blood cells, mainly ]s, generate the inflammation.<ref name=Gary2010/> As well as damaging the lungs, many viruses simultaneously affect other ] and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.<ref name=Viral09>{{cite journal | vauthors = Figueiredo LT | title = Viral pneumonia: epidemiological, clinical, pathophysiological and therapeutic aspects | journal = Jornal Brasileiro de Pneumologia | volume = 35 | issue = 9 | pages = 899–906 | date = September 2009 | pmid = 19820817 | doi = 10.1590/S1806-37132009000900012 | doi-access = free }}</ref>
Initial descriptions of pneumonia focused on the ] or ] appearance of the lung, either by direct inspection at ] or by its appearance under a ]. A ''lobar'' pneumonia is an infection that only involves a single lobe, or section, of a ]. Lobar pneumonia is often due to '']''. ''Multilobar'' pneumonia involves more than one lobe, and it often is a more severe illness than lobar pneumonia. ''Interstitial'' pneumonia involves the areas in between the alveoli, and it may be called "interstitial pneumonitis." Interstitial pneumonia is more likely to be caused by viruses or by atypical bacteria.


==Diagnosis==
The discovery of x-rays made it possible to determine the anatomic type of pneumonia without direct examination of the lungs at autopsy and led to the development of a ] classification. Early investigators distinguished between typical lobar pneumonia and atypical (e.g. Chlamydophila) or viral pneumonia using the location, distribution, and appearance of the opacities they saw on chest x-rays. Certain x-ray findings can be used to help predict the course of illness, although it is not possible to clearly determine the microbiologic cause of a pneumonia based on x-rays alone.
{{listen
| filename =Crackles pneumoniaO.ogg
| title = Crackles
| description = Crackles heard in the lungs of a person with pneumonia using a stethoscope.
| format = ]
}}
Pneumonia is typically diagnosed based on a combination of physical signs and often a ].<ref name=Diag10>{{cite journal | vauthors = Lynch T, Bialy L, Kellner JD, Osmond MH, Klassen TP, Durec T, Leicht R, Johnson DW | title = A systematic review on the diagnosis of pediatric bacterial pneumonia: when gold is bronze | journal = PLOS ONE| volume = 5 | issue = 8 | pages = e11989 | date = August 2010 | pmid = 20700510 | pmc = 2917358 | doi = 10.1371/journal.pone.0011989 | editor1-last = Huicho | bibcode = 2010PLoSO...511989L | editor1-first = Luis | doi-access = free }}</ref> In adults with normal vital signs and a normal lung examination, the diagnosis is unlikely.<ref>{{cite journal | vauthors = Marchello CS, Ebell MH, Dale AP, Harvill ET, Shen Y, Whalen CC | title = Signs and Symptoms That Rule out Community-Acquired Pneumonia in Outpatient Adults: A Systematic Review and Meta-Analysis | journal = Journal of the American Board of Family Medicine | volume = 32 | issue = 2 | pages = 234–47 | date = 2019 | pmid = 30850460 | pmc = 7422644 | doi = 10.3122/jabfm.2019.02.180219 | doi-access = free }}</ref> However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial cause.<ref name=Lancet11/><ref name=Diag10/> The overall impression of a physician appears to be at least as good as decision rules for making or excluding the diagnosis.<ref>{{cite journal | vauthors = Dale AP, Marchello C, Ebell MH | title = Clinical gestalt to diagnose pneumonia, sinusitis, and pharyngitis: a meta-analysis | journal = The British Journal of General Practice | volume = 69 | issue = 684 | pages = e444–e453 | date = July 2019 | pmid = 31208974 | pmc = 6582453 | doi = 10.3399/bjgp19X704297 }}</ref>


===Diagnosis in children===
With the advent of modern microbiology, classification based upon the causative microorganism became possible. Determining which microorganism is causing an individual's pneumonia is an important step in deciding treatment type and length. Sputum cultures, blood cultures, tests on respiratory secretions, and specific blood tests are used to determine the microbiologic classification. Because such laboratory testing typically takes several days, microbiologic classification is usually not possible at the time of initial diagnosis.
The ] has defined pneumonia in children clinically based on either a cough or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness.<ref name=WHOBook/> A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old.<ref name=WHOBook>{{cite book|last1=Ezzati|first1=Majid | last2 = Lopez | first2 = Alan D. | last3 = Rodgers | first3 = Anthony | last4 = Murray | first4 = Christopher J.L. |title=Comparative quantification of health risks|year=2004|publisher=World Health Organization|location=Genève|isbn=978-92-4-158031-1|page=70|url=https://books.google.com/books?id=ACV1jEGx4AgC&pg=PA70}}</ref>


In children, low oxygen levels and lower chest indrawing are more ] than hearing chest ] with a ] or increased respiratory rate.<ref>{{cite journal | vauthors = Shah SN, Bachur RG, Simel DL, Neuman MI | title = Does This Child Have Pneumonia?: The Rational Clinical Examination Systematic Review | journal = JAMA | volume = 318 | issue = 5 | pages = 462–71 | date = August 2017 | pmid = 28763554 | doi = 10.1001/jama.2017.9039 | s2cid = 44974175 }}</ref> Grunting and nasal flaring may be other useful signs in children less than five years old.<ref>{{cite journal | vauthors = Rambaud-Althaus C, Althaus F, Genton B, D'Acremont V | title = Clinical features for diagnosis of pneumonia in children younger than 5 years: a systematic review and meta-analysis | journal = The Lancet. Infectious Diseases | volume = 15 | issue = 4 | pages = 439–50 | date = April 2015 | pmid = 25769269 | doi = 10.1016/s1473-3099(15)70017-4 }}</ref>
===Combined clinical classification===
Traditionally, clinicians have classified pneumonia by clinical characteristics, dividing them into "acute" (less than three weeks duration) and "chronic" pneumonias. This is useful because chronic pneumonias tend to be either non-infectious, or mycobacterial, fungal, or mixed bacterial infections caused by airway obstruction. Acute pneumonias are further divided into the classic bacterial bronchopneumonias (such as '']''), the atypical pneumonias (such as the interstitial pneumonitis of '']'' or '']''), and the aspiration pneumonia syndromes.


Lack of wheezing is an indicator of ''Mycoplasma pneumoniae'' in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not ] treatment should be used.<ref name=Wang2012>{{cite journal | vauthors = Wang K, Gill P, Perera R, Thomson A, Mant D, Harnden A | title = Clinical symptoms and signs for the diagnosis of ''Mycoplasma pneumoniae'' in children and adolescents with community-acquired pneumonia| journal = The Cochrane Database of Systematic Reviews | volume = 2012 | pages = CD009175 | date = October 2012 | issue = 10 | pmid = 23076954 | pmc = 7117561 | doi = 10.1002/14651858.CD009175.pub2 }}</ref> The presence of chest pain in children with pneumonia doubles the probability of ''Mycoplasma pneumoniae''.<ref name=Wang2012/>
The combined clinical classification, now the most commonly used classification scheme, attempts to identify a person's risk factors when he or she first comes to medical attention. The advantage of this classification scheme over previous systems is that it can help guide the selection of appropriate initial treatments even before the microbiologic cause of the pneumonia is known. There are two broad categories of pneumonia in this scheme: Community-acquired pneumonia and hospital-acquired pneumonia.


===Diagnosis in adults===
====''Community-acquired pneumonia''====
In general, in adults, investigations are not needed in mild cases.<ref name=BTS09/> There is a very low risk of pneumonia if all ]s and ] are normal.<ref>{{cite journal | vauthors = Saldías F, Méndez JI, Ramírez D, Díaz O | title = | journal = Revista Médica de Chile | volume = 135 | issue = 4 | pages = 517–28 | date = April 2007 | pmid = 17554463 | doi = 10.4067/s0034-98872007000400016 | doi-access = free }}</ref> ] (CRP) may help support the diagnosis.<ref>{{cite journal | vauthors = Ebell MH, Bentivegna M, Cai X, Hulme C, Kearney M | title = Accuracy of Biomarkers for the Diagnosis of Adult Community-acquired Pneumonia: A Meta-analysis | journal = Academic Emergency Medicine | volume = 27 | issue = 3 | pages = 195–206 | date = March 2020 | pmid = 32100377 | doi = 10.1111/acem.13889 | s2cid = 211523779 | doi-access = free }}</ref> For those with CRP less than 20&nbsp;mg/L without convincing evidence of pneumonia, antibiotics are not recommended.<ref name="Elena 2015"/>
:''Main article: ]''.


] may help determine the cause and support decisions about who should receive antibiotics.<ref name="pmid29037960">{{cite journal | vauthors = Schuetz P, Wirz Y, Sager R, Christ-Crain M, Stolz D, Tamm M, Bouadma L, Luyt CE, Wolff M, Chastre J, Tubach F, Kristoffersen KB, Burkhardt O, Welte T, Schroeder S, Nobre V, Wei L, Bucher HC, Annane D, Reinhart K, Falsey AR, Branche A, Damas P, Nijsten M, de Lange DW, Deliberato RO, Oliveira CF, Maravić-Stojković V, Verduri A, Beghé B, Cao B, Shehabi Y, Jensen JS, Corti C, van Oers JA, Beishuizen A, Girbes AR, de Jong E, Briel M, Mueller B | title = Effect of procalcitonin-guided antibiotic treatment on mortality in acute respiratory infections: a patient level meta-analysis | journal = The Lancet. Infectious Diseases | volume = 18 | issue = 1 | pages = 95–107 | date = January 2018 | pmid = 29037960 | doi = 10.1016/S1473-3099(17)30592-3 | doi-access = free | hdl = 1843/42632 | hdl-access = free }}</ref> Antibiotics are encouraged if the procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L.<ref name="Elena 2015"/> In people requiring hospitalization, ], ] and ]s – including a ], ], C-reactive protein level, and possibly ] – are recommended.<ref name=BTS09/>
] (CAP) is infectious pneumonia in a person who has not recently been hospitalized. CAP is the most common type of pneumonia. The most common causes of CAP differ depending on a person's age, but they include '']'', viruses, the atypical bacteria, and '']''. Overall, ''Streptococcus pneumoniae'' is the most common cause of community-acquired pneumonia worldwide. Gram-negative bacteria cause CAP in certain at-risk populations. CAP is the fourth most common cause of death in the ] and the sixth in the ]. An outdated term, ], has been used to describe a type of community-acquired pneumonia of less severity (hence the fact that the patient can continue to "walk" rather than require hospitalization). Walking pneumonia is usually caused by a virus or by atypical bacteria.


The diagnosis of ] can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing.<ref name=ILI05>{{cite journal | vauthors = Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP | title = Does this patient have influenza? | journal = JAMA | volume = 293 | issue = 8 | pages = 987–97 | date = February 2005 | pmid = 15728170 | doi = 10.1001/jama.293.8.987 }}</ref> Thus, treatment is frequently based on the presence of influenza in the community or a ].<ref name=ILI05/>
====''Hospital-acquired pneumonia''====
{{main|Hospital-acquired pneumonia}}


Adults 65 years old or older, as well as cigarette smokers and people with ongoing medical conditions are at increased risk for pneumonia.<ref>{{cite web |date=30 September 2022 |title=Risk Factors for Pneumonia|url=https://www.cdc.gov/pneumonia/riskfactors.html |access-date=16 January 2023 |website=CDC |language=en-us}}</ref>
Hospital-acquired pneumonia, also called ] pneumonia, is pneumonia acquired during or after hospitalization for another illness or procedure with onset at least 72 hrs after admission. The causes, microbiology, treatment and prognosis are different from those of community-acquired pneumonia. Up to 5% of patients admitted to a hospital for other causes subsequently develop pneumonia. Hospitalized patients may have many risk factors for pneumonia, including ], prolonged ], underlying ] and ] diseases, decreased amounts of stomach acid, and immune disturbances. Additionally, the microorganisms a person is exposed to in a hospital are often different from those at home . Hospital-acquired microorganisms may include resistant bacteria such as ], '']'', '']'', and '']''. Because individuals with hospital-acquired pneumonia usually have underlying illnesses and are exposed to more dangerous bacteria, it tends to be more deadly than community-acquired pneumonia. ] (VAP) is a subset of hospital-acquired pneumonia. VAP is pneumonia which occurs after at least 48 hours of ] and ].


===Other types of pneumonia=== ===Physical exam===
] may sometimes reveal ], ], or low ].<ref name=Clinic2011/> The respiratory rate may be faster than normal, and this may occur a day or two before other signs.<ref name=Clinic2011/><ref name=M32/> Examination of the chest may be normal, but it may show decreased expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed ] breathing and are heard on auscultation with a stethoscope.<ref name=Clinic2011/> Crackles (rales) may be heard over the affected area during ].<ref name=Clinic2011/> ] may be dulled over the affected lung, and increased, rather than decreased, ] distinguishes pneumonia from a ].<ref name=BMJ06/>
*] (SARS)
:SARS is a highly contagious and deadly type of pneumonia which first occurred in 2002 after initial outbreaks in ]. SARS is caused by the ], a previously unknown ]. New cases of SARS have not been seen since June 2003.
*] (BOOP)
:BOOP is caused by inflammation of the small airways of the lungs. It is also known as cryptogenic organizing pneumonitis (COP).
*]
:Eosinophilic pneumonia is invasion of the lung by ]s, a particular kind of ]. Eosinophilic pneumonia often occurs in response to infection with a ] or after exposure to certain types of environmental factors.
*]
:Chemical pneumonia (usually called ]) is caused by chemical ]s such as ]s, which may enter the body by ] or by skin contact. When the toxic substance is an oil, the pneumonia may be called ''lipoid pneumonia''.
*]
:Aspiration pneumonia (or aspiration pneumonitis) is caused by ] foreign objects which are usually oral or gastric contents, either while eating, or after reflux or vomiting which results in ].<ref>{{cite web | url = http://www.kmle.com/search.php?Search=aspiration+pneumonia | title = ''KMLE Medical Dictionary Definition of aspiration pneumonia'' | author = }}</ref> The resulting lung inflammation is not an infection but can contribute to one, since the material aspirated may contain ] bacteria or other unusual causes of pneumonia. Aspiration is a leading cause of death among hospital and ] patients, since they often cannot adequately protect their airways and may have otherwise impaired defenses.


==Treatment== ===Imaging===
]
Most cases of pneumonia can be treated without hospitalization. Typically, oral antibiotics, rest, fluids, and ] are sufficient for complete resolution. However, people with pneumonia who are having trouble breathing, people with other medical problems, and the elderly may need more advanced treatment. If the symptoms get worse, the pneumonia does not improve with home treatment, or complications occur, the person will often have to be hospitalized.
]
A ] is frequently used in diagnosis.<ref name=Develop11/> In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain.<ref name=Develop11/><ref name=BTS09>{{cite journal | vauthors = Lim WS, Baudouin SV, George RC, Hill AT, Jamieson C, Le Jeune I, Macfarlane JT, Read RC, Roberts HJ, Levy ML, Wani M, Woodhead MA | title = BTS guidelines for the management of community acquired pneumonia in adults: update 2009 | journal = Thorax | volume = 64 | issue = Suppl 3 | pages = iii, 1–55 | date = October 2009 | pmid = 19783532 | doi = 10.1136/thx.2009.121434 | doi-access = free }}</ref> If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended.<ref name=BTS09/> Findings do not always match the severity of disease and do not reliably separate between bacterial and viral infection.<ref name=Develop11/>


X-ray presentations of pneumonia may be classified as ], ], ], and ].<ref>{{cite book | editor-last1 = Helms | editor-first1 = Clyde A. | editor-last2=Brant | editor-first2 = William E. | title = Fundamentals of diagnostic radiology | publisher = Wolters Kluwer/Lippincott Williams & Wilkins | location=Philadelphia | isbn=978-1-60831-911-4 | page=435 | url=https://books.google.com/books?id=o_4eoeOinNgC&pg=PA435 | edition=4th | date=20 March 2012}}</ref> Bacterial, community-acquired pneumonia classically show ] of one ], which is known as lobar pneumonia.<ref name=Rad07/> However, findings may vary, and other patterns are common in other types of pneumonia.<ref name=Rad07/> Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side.<ref name=Rad07/> Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation.<ref name=Rad07/> Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to interpret in the ] or those with a history of lung disease.<ref name=Clinic2011/> Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiographs can increase the diagnostic accuracy of lung consolidation and pleural effusion.<ref name="Elena 2015"/>
]s are used to treat bacterial pneumonia. In contrast, antibiotics are not useful for ], although they sometimes are used to treat or prevent bacterial infections that can occur in lungs damaged by a viral pneumonia. The antibiotic choice depends on the nature of the pneumonia, the most common microorganisms causing pneumonia in the local geographic area, and the immune status and underlying health of the individual. Treatment for pneumonia should ideally be based on the causative microorganism and its known ]. However, a specific cause for pneumonia is identified in only 50% of people, even after extensive evaluation. Because treatment should generally not be delayed in any person with a serious pneumonia, ] is usually started well before laboratory reports are available. In the ], ] is the antibiotic selected for most patients with community-acquired pneumonia, sometimes with added ]; patients allergic to ]s are given ] instead of amoxicillin. In ], where the "atypical" forms of community-acquired pneumonia are becoming more common, ], ], and the ] have displaced amoxicillin as first-line treatment. The duration of treatment has traditionally been seven to ten days, but there is increasing evidence that shorter courses (as short as three days) are sufficient.<ref>{{cite journal | author=Pakistan Multicentre Amoxycillin Short Course Therapy (MASCOT) pneumonia study group | title=Clinical efficacy of 3 days versus 5 days of oral amoxicillin for treatment of childhood pneumonia: a multicentre double-blind trial | journal=Lancet | year=2002 | volume=360 | pages=835&ndash;41 | id=PMID 12243918}}</ref><ref>{{cite journal | author= Agarwal G, Awasthi S, Kabra SK, Kaul A, Singhi S, Walter SD; ISCAP Study Group. | title=Three day versus five day treatment with amoxicillin for non-severe pneumonia in young children: a multicentre randomised controlld trial | journal=BMJ | year=2004 | volume=328 | pages=791&ndash;4 | id=PMID 15070633}}</ref><ref>{{cite journal | author=el Moussaoui R, de Borgie CA, van den Broek P, Hustinx WN, Bresser P, van den Berk GE, Poley JW, van den Berg B, Krouwels FH, Bonten MJ, Weenink C, Bossuyt PM, Speelman P, Opmeer BC, Prins JM. | title=Effictiveness of discontinuing antibiotic treatment after three days versus eight days in mild to moderate-severe community acquired pneumonia: randomised, double blind study | journal=BMJ | year=2006 | volume=332 | pages=1355&ndash;58 | id=PMID 16763247}}</ref>


A ] can give additional information in indeterminate cases<ref name=Rad07/> and provide more details in those with an unclear chest radiograph (for example occult pneumonia in chronic obstructive pulmonary disease). They can be used to exclude ] and ], and detect lung abscesses in those who are not responding to treatments.<ref name="Elena 2015"/> However, CT scans are more expensive, have a higher dose of radiation, and cannot be done at bedside.<ref name="Elena 2015"/>
Antibiotics for hospital-acquired pneumonia include ], third- and fourth-generation ], ]s, ], and ]s. These antibiotics are usually given ]. Multiple antibiotics may be administered in combination in an attempt to treat all of the possible causative microorganisms. Antibiotic choices vary from hospital to hospital because of regional differences in the most likely microorganisms, and because of differences in the microorganisms' abilities to resist various antibiotic treatments.


] may also be useful in helping to make the diagnosis.<ref>{{cite journal |vauthors=Llamas-Álvarez AM, Tenza-Lozano EM, Latour-Pérez J |date=February 2017 |title=Accuracy of Lung Ultrasonography in the Diagnosis of Pneumonia in Adults: Systematic Review and Meta-Analysis |url=https://journal.chestnet.org/article/S0012-3692(16)62327-9/fulltext |journal=Chest |volume=151 |issue=2 |pages=374–82 |doi=10.1016/j.chest.2016.10.039 |pmid=27818332 |s2cid=24399240}}</ref> Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings.<ref name="Elena 2015"/> It may be more accurate than chest X-ray.<ref>{{cite journal | vauthors = Ye X, Xiao H, Chen B, Zhang S | title = Accuracy of Lung Ultrasonography versus Chest Radiography for the Diagnosis of Adult Community-Acquired Pneumonia: Review of the Literature and Meta-Analysis | journal = PLOS ONE| volume = 10 | issue = 6 | pages = e0130066 | date = 2015 | pmid = 26107512 | pmc = 4479467 | doi = 10.1371/journal.pone.0130066 | bibcode = 2015PLoSO..1030066Y | doi-access = free }}</ref>
People who have difficulty breathing due to pneumonia may require extra ]. Extremely sick individuals may require ], often including ] and ].


<gallery>
] caused by influenza A may be treated with ] or ], while viral pneumonia caused by influenza A or B may be treated with ] or ]. These treatments are beneficial only if they are started within 48 hours of the onset of symptoms. Many strains of ] influenza A, also known as ] or "bird flu," have shown resistance to rimantadine and amantadine. There are no known effective treatments for viral pneumonias caused by the ], ], ], or ] virus.
File:UOTW 34 - Ultrasound of the Week 1.webm|Pneumonia seen by ultrasound<ref name=UOTW34>{{cite web|title=UOTW No. 34 – Ultrasound of the Week|url=https://www.ultrasoundoftheweek.com/uotw-34/|website=Ultrasound of the Week|access-date=27 May 2017|date=20 January 2015|url-status=live|archive-url=https://web.archive.org/web/20170509114431/https://www.ultrasoundoftheweek.com/uotw-34/|archive-date=9 May 2017}}</ref>
File:UOTW 34 - Ultrasound of the Week 2.webm|Pneumonia seen by ultrasound<ref name=UOTW34/>
File:UOTW 34 - Ultrasound of the Week 3.jpg|Pneumonia seen by ultrasound<ref name=UOTW34/>
File:RtPneuKidMark.png|Right middle lobe pneumonia in a child as seen on plain X-ray
</gallery>


==Complications== ===Microbiology===
In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management.<ref name=Develop11/> For people who do not respond to treatment, ] should be considered, and culture for ''Mycobacterium tuberculosis'' should be carried out in persons with a chronic productive cough.<ref name=BTS09/> Microbiological evaluation is also indicated in severe pneumonia, alcoholism, ], immunosuppression, HIV infection, and those being empirically treated for MRSA of pseudomonas.<ref name="Elena 2015"/><ref name=Met2019>{{cite journal | vauthors = Metlay JP, Waterer GW, Long AC, Anzueto A, Brozek J, Crothers K, Cooley LA, Dean NC, Fine MJ, Flanders SA, Griffin MR, Metersky ML, Musher DM, Restrepo MI, Whitney CG | title = Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America | journal = American Journal of Respiratory and Critical Care Medicine | volume = 200 | issue = 7 | pages = e45–e67 | date = October 2019 | pmid = 31573350 | pmc = 6812437 | doi = 10.1164/rccm.201908-1581ST }}</ref> Although positive ] and ] culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of ] of respiratory tract.<ref name="Elena 2015"/> Testing for other specific organisms may be recommended during outbreaks, for public health reasons.<ref name=BTS09/> In those hospitalized for severe disease, both sputum and ] are recommended,<ref name=BTS09/> as well as testing the urine for ]s to ''Legionella'' and ''Streptococcus''.<ref name=IDSA2007/> Viral infections, can be confirmed via detection of either the virus or its antigens with ] or ] (PCR), among other techniques.<ref name=Lancet11/> ''Mycoplasma'', ''Legionella'', ''Streptococcus'', and ''Chlamydia'' can also be detected using PCR techniques on ] and ].<ref name="Elena 2015"/> The causative agent is determined in only 15% of cases with routine microbiological tests.<ref name=BMJ06/>
Sometimes pneumonia can lead to additional ]. Complications are more frequently associated with bacterial pneumonia than with viral pneumonia. The most important complications include:


===Classification===
===Respiratory and circulatory failure===
{{Main|Classification of pneumonia}}
Because pneumonia affects the lungs, often people with pneumonia have difficulty breathing, and it may not be possible for them to breathe well enough to stay alive without support. Non-invasive breathing assistance may be helpful, such as with a ] machine. In other cases, placement of an ] (breathing tube) may be necessary, and a ] may be used to help the person breathe.
''Pneumonitis'' refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of ].<ref>{{cite book|title=Stedman's medical dictionary.|url=https://archive.org/details/stedmansmedicald00sted_3|url-access=registration|year=2006|publisher=Lippincott Williams & Wilkins|location=Philadelphia|isbn=978-0-7817-6450-6|edition=28th}}</ref> Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, ], ], and ventilator-associated pneumonia.<ref name=Rad07>{{cite journal | vauthors = Sharma S, Maycher B, Eschun G | title = Radiological imaging in pneumonia: recent innovations | journal = Current Opinion in Pulmonary Medicine | volume = 13 | issue = 3 | pages = 159–69 | date = May 2007 | pmid = 17414122 | doi = 10.1097/MCP.0b013e3280f3bff4 | s2cid = 39554602 }}</ref> It may also be classified by the area of the lung affected: lobar, ] and ];<ref name=Rad07/> or by the causative organism.<ref>{{cite journal |vauthors=Dunn L |date=29 June – 5 July 2005 |title=Pneumonia: classification, diagnosis and nursing management |url=https://journals.rcni.com/doi/abs/10.7748/ns2005.06.19.42.50.c3901 |journal=Nursing Standard |volume=19 |issue=42 |pages=50–54 |doi=10.7748/ns2005.06.19.42.50.c3901 |pmid=16013205}}</ref> Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.<ref>{{cite book |url=https://books.google.com/books?id=xbkbRG5XYxsC&pg=PA72 |title=Pocket Book of Hospital Care for Children: Guidelines for the Management of Common Illnesses with Limited Resources |publisher=World Health Organization |year=2005 |isbn=978-92-4-154670-6 |location=Geneva |page=72}}</ref>


The setting in which pneumonia develops is important to treatment,<ref name="Ana2009">{{cite journal |vauthors=Anand N, Kollef MH |date=February 2009 |title=The alphabet soup of pneumonia: CAP, HAP, HCAP, NHAP, and VAP |journal=Seminars in Respiratory and Critical Care Medicine |volume=30 |issue=1 |pages=3–9 |doi=10.1055/s-0028-1119803 |pmid=19199181|s2cid=260320494 }}</ref><ref name=ATS2005/> as it correlates to which pathogens are likely suspects,<ref name=Ana2009/> which mechanisms are likely, which antibiotics are likely to work or fail,<ref name=Ana2009/> and which complications can be expected based on the person's health status.
Pneumonia can also cause respiratory failure by triggering ] (ARDS), which results from a combination of infection and inflammatory response. The lungs quickly fill with fluid and become very stiff. This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, create a need for mechanical ventilation.
]
] and ] are potential complications of pneumonia. Sepsis occurs when microorganisms enter the bloodstream and the ] responds by secreting ]. Sepsis most often occurs with ]; ''Streptococcus pneumoniae'' is the most common cause. Individuals with sepsis or septic shock need hospitalization in an ]. They often require ]s and medications to help keep their blood pressure from dropping too low. Sepsis can cause liver, kidney, and heart damage, among other problems, and it often causes death.


====Community====
===Pleural effusion, empyema, and abscess===
{{Main|Community-acquired pneumonia}}
Occasionally, microorganisms infecting the lung will cause fluid (a ]) to build up in the space that surrounds the lung (the ]). If the microorganisms themselves are present in the pleural cavity, the fluid collection is called an ]. When pleural fluid is present in a person with pneumonia, the fluid can often be collected with a needle (]) and examined. Depending on the results of this examination, complete drainage of the fluid may be necessary, often requiring a ]. In severe cases of empyema, ] may be needed. If the fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity.
Community-acquired pneumonia (CAP) is acquired in the community,<ref name=Ana2009/><ref name=ATS2005/> outside of health care facilities. Compared with healthcare-associated pneumonia, it is less likely to involve ] bacteria. Although the latter are no longer rare in CAP,<ref name=Ana2009/> they are still less likely. Prior stays in healthcare-related environments such as hospitals, nursing homes, or hemodialysis centers or a history of receiving domiciliary care can increase patients' risk for CAP caused by multidrug-resistant bacteria.<ref>{{cite journal |last1=Falcone |first1=Marco |last2=Russo |first2=Alessandro |last3=Giannella |first3=Maddalena |last4=Cangemi |first4=Roberto |last5=Scarpellini |first5=Maria Gabriella |last6=Bertazzoni |first6=Giuliano |last7=Alarcón |first7=José Martínez |last8=Taliani |first8=Gloria |last9=Palange |first9=Paolo |last10=Farcomeni |first10=Alessio |last11=Vestri |first11=Annarita |last12=Bouza |first12=Emilio |last13=Violi |first13=Francesco |last14=Venditti |first14=Mario |date=10 April 2015 |editor-last=Salluh |editor-first=Jorge IF |title=Individualizing Risk of Multidrug-Resistant Pathogens in Community-Onset Pneumonia |journal=PLOS ONE |language=en |volume=10 |issue=4 |pages=e0119528 |doi=10.1371/journal.pone.0119528 |issn=1932-6203 |pmc=4393134 |pmid=25860142|bibcode=2015PLoSO..1019528F |doi-access=free }}</ref>


====Healthcare====
Rarely, bacteria in the lung will form a pocket of infected fluid called an ]. Lung abscesses can usually be seen with a chest x-ray or chest CT scan. Abscesses typically occur in ] and often contain several types of bacteria. Antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a ] or ].
Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system,<ref name=Ana2009/> including hospitals, outpatient clinics, ]s, ] centers, ] treatment, or ].<ref name=ATS2005/> HCAP is sometimes called MCAP (medical care–associated pneumonia).


People may become infected with pneumonia in a hospital; this is defined as pneumonia not present at the time of admission (symptoms must start at least 48 hours after admission).<ref name="ATS2005">{{cite journal |author1=American Thoracic Society |author2=Infectious Diseases Society of America |date=February 2005 |title=Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia |url=https://www.atsjournals.org/doi/10.1164/rccm.200405-644ST |journal=American Journal of Respiratory and Critical Care Medicine |volume=171 |issue=4 |pages=388–416 |doi=10.1164/rccm.200405-644ST |pmid=15699079}}</ref><ref name=Ana2009/> It is likely to involve ]s, with higher risk of ] pathogens. People in a hospital often have other medical conditions, which may make them more susceptible to pathogens in the hospital.
==Prognosis and mortality==
With treatment, most types of bacterial pneumonia can be cured within one to two weeks.{{Fact|article|date=June 2007}} Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely.{{Fact|article|date=June 2007}} The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.{{Fact|article|date=June 2007}}


Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation.<ref name=Ana2009/><ref name=Ar2016/> Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after ].<ref name=ATS2005/>
In the United States, about one of every twenty people with ] will die.{{Fact|article|date=June 2007}} In cases where the pneumonia progresses to blood poisoning (]), one of every five will die.{{Fact|article|date=June 2007}} The death rate (or ]) also depends on the underlying cause of the pneumonia. Pneumonia caused by ''Mycoplasma'', for instance, is associated with little mortality. However, about half of the people who develop methicillin-resistant ''Staphylococcus aureus'' (]) pneumonia while on a ventilator will die.<ref name=combes>Combes A, Luyt CE, Fagon JY, Wollf M, Trouillet JL, Gibert C, Chastre J; PNEUMA Trial Group. Impact of methicillin resistance on outcome of Staphylococcus aureus ventilator-associated pneumonia.'' Am J Respir Crit Care Med''. 2004 Oct 1;170(7):786-92. PMID 15242840</ref> In regions of the world without advanced health care systems, pneumonia is even deadlier. Limited access to clinics and hospitals, limited access to x-rays, limited antibiotic choices, and inability to treat underlying conditions inevitably leads to higher rates of death from pneumonia.


===Differential diagnosis===
===Clinical prediction rules===
Several diseases can present with similar signs and symptoms to pneumonia, such as: chronic obstructive pulmonary disease, asthma, ], ], lung cancer, and ].<ref name=BMJ06/> Unlike pneumonia, asthma and COPD typically present with wheezing, pulmonary edema presents with an abnormal ], cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli present with acute onset sharp chest pain and shortness of breath.<ref name=BMJ06/> Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from ]. Pulmonary infiltrates that resolved after giving mechanical ventilation should point to heart failure and ] rather than pneumonia. For recurrent pneumonia, underlying lung cancer, ], tuberculosis, a foreign bodies, immunosuppression, and hypersensitivity should be suspected.<ref name="Elena 2015">{{cite journal | vauthors = Prina E, Ranzani OT, Torres A | title = Community-acquired pneumonia | journal = Lancet | volume = 386 | issue = 9998 | pages = 1097–108 | date = September 2015 | pmid = 26277247 | pmc = 7173092 | doi = 10.1016/S0140-6736(15)60733-4 }}</ref>
Clinical prediction rules have been developed to more objectively prognosticate outcomes in pneumonia. These rules can be helpful in deciding whether or not to hospitalize the person.
* ]<ref name=fine>Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. A prediction rule to identify low-risk patients with community-acquired pneumonia. ''N Engl J Med''. 1997 Jan 23;336(4):243–250. PMID 8995086</ref> -
* ] score, which takes into account the severity of symptoms, any underlying diseases, and age<ref name="pmid12728155">{{cite journal |author=Lim WS, van der Eerden MM, Laing R, ''et al'' |title=Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study |journal=Thorax |volume=58 |issue=5 |pages=377-82 |year=2003 |pmid=12728155 |doi=}}</ref> -


==Prevention== ==Prevention==
Prevention includes ], environmental measures, and appropriate treatment of other health problems.<ref name=Develop11/> It is believed that, if appropriate preventive measures were instituted globally, mortality among children could be reduced by 400,000; and, if proper treatment were universally available, childhood deaths could be decreased by another 600,000.<ref name=WHOPrevent2012/>
There are several ways to prevent infectious pneumonia. Appropriately treating underlying illnesses (such as ]) can decrease a person's risk of pneumonia. ] is important not only because it helps to limit lung damage, but also because cigarette smoke interferes with many of the body's natural defenses against pneumonia.


===Vaccination===
] shows that there are several ways to prevent pneumonia in newborn ]s. Testing pregnant women for ] and '']'', and then giving ] treatment if needed, reduces pneumonia in infants. Suctioning the mouth and throat of infants with ]-stained ] decreases the rate of ].
Vaccination prevents against certain bacterial and viral pneumonias both in children and adults. ]s are modestly effective at preventing symptoms of influenza,<ref name=Lancet11/><ref>{{cite journal | vauthors = Demicheli V, Jefferson T, Ferroni E, Rivetti A, Di Pietrantonj C | title = Vaccines for preventing influenza in healthy adults | journal = The Cochrane Database of Systematic Reviews | volume = 2020 | pages = CD001269 | date = February 2018 | issue = 2 | pmid = 29388196 | pmc = 6491184 | doi = 10.1002/14651858.CD001269.pub6 }}</ref> The ] (CDC) recommends yearly influenza vaccination for every person 6&nbsp;months and older.<ref>{{cite web|title=Seasonal Influenza (Flu)|url=https://www.cdc.gov/flu/|work=Centers for Disease Control and Prevention|access-date=29 June 2011|url-status=live|archive-url=https://web.archive.org/web/20110629190823/http://www.cdc.gov/flu/|archive-date=29 June 2011}}</ref> Immunizing health care workers decreases the risk of viral pneumonia among their patients.<ref name=IDSA2007>{{cite journal | vauthors = Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG | title = Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults | journal = Clinical Infectious Diseases | volume = 44 | issue = Suppl 2 | pages = S27–72 | date = March 2007 | pmid = 17278083 | pmc = 7107997 | doi = 10.1086/511159 | doi-access = free }}</ref>


Vaccinations against ''Haemophilus influenzae'' and ''Streptococcus pneumoniae'' have good evidence to support their use.<ref name=PedNA09/> There is strong evidence for vaccinating children under the age of 2 against ''Streptococcus pneumoniae'' (]).<ref>{{cite journal | vauthors = Lucero MG, Dulalia VE, Nillos LT, Williams G, Parreño RA, Nohynek H, Riley ID, Makela H | title = Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and X-ray defined pneumonia in children less than two years of age | journal = The Cochrane Database of Systematic Reviews | issue = 4 | pages = CD004977 | date = October 2009 | volume = 2009 | pmid = 19821336 | pmc = 6464899 | doi = 10.1002/14651858.CD004977.pub2 }}</ref><ref>{{cite web|url=https://www.who.int/biologicals/areas/vaccines/pneumo/en/|archive-url=https://web.archive.org/web/20080428235941/http://www.who.int/biologicals/areas/vaccines/pneumo/en/|archive-date=28 April 2008|title=WHO {{!}} Pneumococcal conjugate vaccines|website=who.int|access-date=16 January 2018}}</ref><ref name=CDC2018Vac>{{cite web|url=https://www.cdc.gov/pneumococcal/vaccination.html|title=Pneumococcal Disease {{!}} Vaccines – PCV13 and PPSV23 {{!}} CDC|date=18 September 2017|website=cdc.gov|language=en-us|access-date=16 January 2018}}</ref> Vaccinating children against ''Streptococcus pneumoniae'' has led to a decreased rate of these infections in adults, because many adults acquire infections from children. A ] is available for adults, and has been found to decrease the risk of ] by 74%, but there is insufficient evidence to suggest using the pneumococcal vaccine to prevent pneumonia or death in the general adult population.<ref>{{cite journal | vauthors = Moberley S, Holden J, Tatham DP, Andrews RM | title = Vaccines for preventing pneumococcal infection in adults | journal = The Cochrane Database of Systematic Reviews | volume = 1 | issue = 1 | pages = CD000422 | date = January 2013 | pmid = 23440780 | pmc = 7045867 | doi = 10.1002/14651858.CD000422.pub3 }}</ref> The CDC recommends that young children and adults over the age of 65 receive the pneumococcal vaccine, as well as older children or younger adults who have an increased risk of getting pneumococcal disease.<ref name=CDC2018Vac/> The pneumococcal vaccine has been shown to reduce the risk of community acquired pneumonia in people with chronic obstructive pulmonary disease, but does not reduce mortality or the risk of hospitalization for people with this condition.<ref name=Walters2017>{{cite journal | vauthors = Walters JA, Tang JN, Poole P, Wood-Baker R | title = Pneumococcal vaccines for preventing pneumonia in chronic obstructive pulmonary disease | journal = The Cochrane Database of Systematic Reviews | volume = 1 | pages = CD001390 | date = January 2017 | issue = 3 | pmid = 28116747 | pmc = 6422320 | doi = 10.1002/14651858.CD001390.pub4 }}</ref> People with COPD are recommended by a number of guidelines to have a pneumococcal vaccination.<ref name=Walters2017 /><!-- Quote = respiratory guidelines in Europe (ERS 2014) and Australia (COPDX 2016) recommend immunisation with the PPV‐23 polysaccharide pneumococcal vaccine for adults at risk of pneumococcal disease, including those with COPD... Major COPD guidelines (COPDX 2016; ERS 2014; GOLD 2016; NICE 2010) have recommended pneumococcal vaccination --> Other vaccines for which there is support for a protective effect against pneumonia include ], ], and ].<ref name=CDCPrev2012/>
] is important for preventing pneumonia in both children and adults. Vaccinations against '']'' and '']'' in the first year of life have greatly reduced their role in pneumonia in children. Vaccinating children against ''Streptococcus pneumoniae'' has also led to a decreased incidence of these infections in adults because many adults acquire infections from children. A ] is also available for adults. In the U.S., it is currently recommended for all healthy individuals older than 65 and any adults with ], ], ], ] of the ], ], ] leaks, or those who do not have a ]. A repeat vaccination may also be required after five or ten years.<ref name=butler>Butler JC, Breiman RF, Campbell JF, Lipman HB, Broome CV, Facklam RR. Pneumococcal polysaccharide vaccine efficacy: an evaluation of current recommendations.'' JAMA'' 1993;270:1826–1831. PMID 8411526</ref>


===Medications===
] vaccines should be given yearly to the same individuals who receive vaccination against '']''. In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine.<ref name=CDC>Centers for Disease Control and Prevention. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP)''. MMWR'' 1999;48(RR-4):1–28. PMID 10366138.</ref> When an influenza outbreak is occurring, medications such as ], ], ], and ] can help prevent influenza.<ref name=jefferson>Jefferson T, Deeks JJ, Demicheli V, Rivetti D, Rudin M. Amantadine and rimantadine for preventing and treating influenza A in adults. ''Cochrane Database Syst Rev.'' 2004;(3):CD001169. PMID 15266442</ref><sup>,</sup><ref name=hayden>Hayden FG, Atmar RL, Schilling M, Johnson C, Poretz D, Paar D, Huson L, Ward P, Mills RG. Use of the selective oral neuraminidase inhibitor oseltamivir to prevent influenza.'' N Engl J Med'' 1999;341:1336–1343 PMID 10536125</ref>
When influenza outbreaks occur, medications such as ] or ] may help prevent the condition, but they are associated with side effects.<ref name=jefferson>{{cite journal | vauthors = Jefferson T, Demicheli V, Di Pietrantonj C, Rivetti D | title = Amantadine and rimantadine for influenza A in adults | journal = The Cochrane Database of Systematic Reviews | issue = 2 | pages = CD001169 | date = April 2006 | volume = 2006 | pmid = 16625539 | pmc = 7068158 | doi = 10.1002/14651858.CD001169.pub3 }}</ref> ] or ] decrease the chance that people who are exposed to the virus will develop symptoms; however, it is recommended that potential side effects are taken into account.<ref>{{cite journal | vauthors = Jefferson T, Jones MA, Doshi P, Del Mar CB, Hama R, Thompson MJ, Spencer EA, Onakpoya I, Mahtani KR, Nunan D, Howick J, Heneghan CJ | title = Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children | journal = The Cochrane Database of Systematic Reviews | volume = 4 | issue = 4 | pages = CD008965 | date = April 2014 | pmid = 24718923 | pmc = 6464969 | doi = 10.1002/14651858.CD008965.pub4 }}</ref>

===Other===
]<ref name=BTS09/> and reducing ], such as that from cooking indoors with wood, crop residues or ], are both recommended.<ref name=Develop11/><ref name=WHOPrevent2012/> Smoking appears to be the single biggest risk factor for ] in otherwise-healthy adults.<ref name=IDSA2007/> Hand hygiene and coughing into one's sleeve may also be effective preventative measures.<ref name=CDCPrev2012/> Wearing ] by the sick may also prevent illness.<ref name=IDSA2007/>

Appropriately treating underlying illnesses (such as HIV/AIDS, ], and malnutrition) can decrease the risk of pneumonia.<ref name=WHOPrevent2012>{{cite web|title=Pneumonia (Fact sheet N°331)|url=https://www.who.int/mediacentre/factsheets/fs331/en/|work=World Health Organization|date=August 2012|url-status=live|archive-url=https://web.archive.org/web/20120830053348/http://www.who.int/mediacentre/factsheets/fs331/en/|archive-date=30 August 2012}}</ref><ref name=CDCPrev2012>{{cite web|title=Pneumonia Can Be Prevented – Vaccines Can Help|url=https://www.cdc.gov/features/Pneumonia/|work=Centers for Disease Control and Prevention|access-date=22 October 2012|url-status=live|archive-url=https://web.archive.org/web/20121023024453/http://www.cdc.gov/features/Pneumonia/|archive-date=23 October 2012}}</ref><ref>{{cite journal |vauthors=Gray DM, Zar HJ |date=May 2010 |title=Community-acquired pneumonia in HIV-infected children: a global perspective |url=https://journals.lww.com/co-pulmonarymedicine/Abstract/2010/05000/Community_acquired_pneumonia_in_HIV_infected.8.aspx |journal=Current Opinion in Pulmonary Medicine |volume=16 |issue=3 |pages=208–16 |doi=10.1097/MCP.0b013e3283387984 |pmid=20375782 |s2cid=23778903}}</ref> In children less than 6&nbsp;months of age, exclusive breast feeding reduces both the risk and severity of disease.<ref name=WHOPrevent2012/> In people with HIV/AIDS and a CD4 count of less than 200 cells/uL the antibiotic ] decreases the risk of ''Pneumocystis pneumonia''<ref>{{cite journal | vauthors = Huang L, Cattamanchi A, Davis JL, den Boon S, Kovacs J, Meshnick S, Miller RF, Walzer PD, Worodria W, Masur H | title = HIV-associated Pneumocystis pneumonia | journal = Proceedings of the American Thoracic Society | volume = 8 | issue = 3 | pages = 294–300 | date = June 2011 | pmid = 21653531 | pmc = 3132788 | doi = 10.1513/pats.201009-062WR }}</ref> and is also useful for prevention in those that are immunocompromised but do not have HIV.<ref>{{cite journal | vauthors = Stern A, Green H, Paul M, Vidal L, Leibovici L | title = Prophylaxis for Pneumocystis pneumonia (PCP) in non-HIV immunocompromised patients | journal = The Cochrane Database of Systematic Reviews | volume = 10 | issue = 10 | pages = CD005590 | date = October 2014 | pmid = 25269391 | pmc = 6457644 | doi = 10.1002/14651858.CD005590.pub3 }}</ref>

Testing pregnant women for ] and '']'', and administering ] treatment, if needed, reduces rates of pneumonia in infants;<ref>{{cite journal | vauthors = Taminato M, Fram D, Torloni MR, Belasco AG, Saconato H, Barbosa DA | title = Screening for group B Streptococcus in pregnant women: a systematic review and meta-analysis | journal = Revista Latino-Americana de Enfermagem | volume = 19 | issue = 6 | pages = 1470–78 | date = November–December 2011 | pmid = 22249684 | doi = 10.1590/s0104-11692011000600026 | doi-access = free }}</ref><ref>{{cite journal |vauthors=Darville T |date=October 2005 |title=Chlamydia trachomatis infections in neonates and young children |url=https://www.sciencedirect.com/science/article/abs/pii/S104518700500066X |journal=Seminars in Pediatric Infectious Diseases |volume=16 |issue=4 |pages=235–44 |doi=10.1053/j.spid.2005.06.004 |pmid=16210104}}</ref> preventive measures for HIV transmission from mother to child may also be efficient.<ref>{{cite book|title=Global Action Plan for Prevention and Control of Pneumonia (GAPP)|year=2009|publisher=World Health Organization|url=http://whqlibdoc.who.int/hq/2009/WHO_FCH_CAH_NCH_09.04_eng.pdf|url-status=live|archive-url=https://web.archive.org/web/20131017001256/http://whqlibdoc.who.int/hq/2009/WHO_FCH_CAH_NCH_09.04_eng.pdf|archive-date=17 October 2013}}</ref> Suctioning the mouth and throat of infants with ]-stained ] has not been found to reduce the rate of aspiration pneumonia and may cause potential harm,<ref name="Rog2009">{{cite journal |vauthors=Roggensack A, Jefferies AL, Farine D |date=April 2009 |title=Management of meconium at birth |url=https://www.sciencedirect.com/science/article/abs/pii/S1701216316341536 |journal=Journal of Obstetrics and Gynaecology Canada |volume=31 |issue=4 |pages=353–54 |doi=10.1016/s1701-2163(16)34153-6 |pmid=19497156}}</ref> thus this practice is not recommended in the majority of situations.<ref name=Rog2009/> In the frail elderly good oral health care may lower the risk of aspiration pneumonia,<ref>{{cite journal |vauthors=van der Maarel-Wierink CD, Vanobbergen JN, Bronkhorst EM, Schols JM, de Baat C |date=March 2013 |title=Oral health care and aspiration pneumonia in frail older people: a systematic literature review |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1741-2358.2012.00637.x |journal=Gerodontology |volume=30 |issue=1 |pages=3–9 |doi=10.1111/j.1741-2358.2012.00637.x |pmid=22390255}}</ref> even though there is no good evidence that one approach to mouth care is better than others in preventing nursing home acquired pneumonia.<ref>{{cite journal |vauthors=Cao Y, Liu C, Lin J, Ng L, Needleman I, Walsh T, Li C |date=September 2018 |title=Oral care measures for preventing nursing home-acquired pneumonia |url= |journal=The Cochrane Database of Systematic Reviews |volume= 2022|issue= 11|pages= CD012416|doi=10.1002/14651858.CD012416.pub3 |pmc= 9668328|pmid=36383760}}</ref> ] in children 2 months to five years old appears to reduce rates of pneumonia.<ref>{{cite journal | vauthors = Lassi ZS, Moin A, Bhutta ZA | title = Zinc supplementation for the prevention of pneumonia in children aged 2 months to 59 months | journal = The Cochrane Database of Systematic Reviews | volume = 12 | pages = CD005978 | date = December 2016 | issue = 12 | pmid = 27915460 | pmc = 6463931 | doi = 10.1002/14651858.CD005978.pub3 }}</ref>

For people with low levels of ] in their diet or blood, taking vitamin C supplements may be suggested to decrease the risk of pneumonia, although there is no strong evidence of benefit.<ref name=":0" /> There is insufficient evidence to recommend that the general population take vitamin C to prevent or treat pneumonia.<ref name=":0">{{cite journal | vauthors = Padhani ZA, Moazzam Z, Ashraf A, Bilal H, Salam RA, Das JK, Bhutta ZA | title = Vitamin C supplementation for prevention and treatment of pneumonia | journal = The Cochrane Database of Systematic Reviews | volume = 4 | pages = CD013134 | date = 18 November 2021 | issue = 11 | pmid = 34791642 | pmc = 8599445 | doi = 10.1002/14651858.CD013134.pub3 }}</ref>

For adults and children in the hospital who require a respirator, there is no strong evidence indicating a difference between ]s and ] for preventing pneumonia.<ref>{{cite journal | vauthors = Gillies D, Todd DA, Foster JP, Batuwitage BT | title = Heat and moisture exchangers versus heated humidifiers for mechanically ventilated adults and children | journal = The Cochrane Database of Systematic Reviews | volume = 9 | pages = CD004711 | date = September 2017 | issue = 12 | pmid = 28905374 | pmc = 6483749 | doi = 10.1002/14651858.CD004711.pub3 }}</ref> There is tentative evidence that laying flat on the back compared to semi-raised increases pneumonia risks in people who are intubated.<ref>{{cite journal | vauthors = Wang L, Li X, Yang Z, Tang X, Yuan Q, Deng L, Sun X | title = Semi-recumbent position versus supine position for the prevention of ventilator-associated pneumonia in adults requiring mechanical ventilation | journal = The Cochrane Database of Systematic Reviews | issue = 1 | pages = CD009946 | date = January 2016 | volume = 2016 | pmid = 26743945 | pmc = 7016937 | doi = 10.1002/14651858.CD009946.pub2 }}</ref>

==Management==
{|class="wikitable" align="right" style="margin-left:0.4em;"
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!colspan=2| ]
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! Symptom !! Points
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| '''C'''onfusion ||style="text-align: center;"|1
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| '''U'''rea>7&nbsp;mmol/L ||style="text-align: center;"|1
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| '''R'''espiratory rate>30 ||style="text-align: center;"|1
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| ]<90mmHg, D'''B'''P<60mmHg||style="text-align: center;"|1
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| Age>='''65''' ||style="text-align: center;"|1
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] by mouth, rest, simple ], and fluids usually suffice for complete resolution.<ref name=BTS09/> However, those with other medical conditions, the elderly, or those with significant trouble breathing may require more advanced care. If the symptoms worsen, the pneumonia does not improve with home treatment, or complications occur, hospitalization may be required.<ref name=BTS09/> Worldwide, approximately 7–13% of cases in children result in hospitalization,<ref name=Develop11/> whereas in the developed world between 22 and 42% of adults with community-acquired pneumonia are admitted.<ref name=BTS09/> The ] score is useful for determining the need for admission in adults.<ref name=BTS09/> If the score is 0 or 1, people can typically be managed at home; if it is 2, a short hospital stay or close follow-up is needed; if it is 3–5, hospitalization is recommended.<ref name=BTS09/> In children those with ] or oxygen saturations of less than 90% should be hospitalized.<ref name=PIDS11>{{cite journal | vauthors = Bradley JS, Byington CL, Shah SS, Alverson B, Carter ER, Harrison C, Kaplan SL, Mace SE, McCracken GH, Moore MR, St Peter SD, Stockwell JA, Swanson JT | title = The management of community-acquired pneumonia in infants and children older than 3 months of age: clinical practice guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America | journal = Clinical Infectious Diseases | volume = 53 | issue = 7 | pages = e25–76 | date = October 2011 | pmid = 21880587 | pmc = 7107838 | doi = 10.1093/cid/cir531 | doi-access = free }}</ref> The utility of ] in pneumonia has not yet been determined.<ref>{{cite journal | vauthors = Chaves GS, Freitas DA, Santino TA, Nogueira PA, Fregonezi GA, Mendonça KM | title = Chest physiotherapy for pneumonia in children | journal = The Cochrane Database of Systematic Reviews | volume = 1 | pages = CD010277 | date = January 2019 | issue = 9 | pmid = 30601584 | pmc = 6353233 | doi = 10.1002/14651858.CD010277.pub3 }}</ref><ref>{{cite journal |last1=Chen |first1=Xiaomei |last2=Jiang |first2=Jiaojiao |last3=Wang |first3=Renjie |last4=Fu |first4=Hongbo |last5=Lu |first5=Jing |last6=Yang |first6=Ming |date=6 September 2022 |title=Chest physiotherapy for pneumonia in adults |journal=The Cochrane Database of Systematic Reviews |volume=2022 |issue=9 |pages=CD006338 |doi=10.1002/14651858.CD006338.pub4 |issn=1469-493X |pmc=9447368 |pmid=36066373}}</ref> Over-the-counter ] has not been found to be effective,<ref name="Chang2014">{{cite journal |vauthors=Chang CC, Cheng AC, Chang AB |date=March 2014 |title=Over-the-counter (OTC) medications to reduce cough as an adjunct to antibiotics for acute pneumonia in children and adults |journal=The Cochrane Database of Systematic Reviews |volume=2014 |issue=3 |pages=CD006088 |doi=10.1002/14651858.CD006088.pub4 |pmid=24615334|doi-access=free |pmc=11023600 }}</ref> nor has the use of zinc supplementation in children.<ref>{{cite journal | vauthors = Haider BA, Lassi ZS, Ahmed A, Bhutta ZA | title = Zinc supplementation as an adjunct to antibiotics in the treatment of pneumonia in children 2 to 59 months of age | journal = The Cochrane Database of Systematic Reviews | issue = 10 | pages = CD007368 | date = October 2011 | volume = 2013 | pmid = 21975768 | pmc = 7000651 | doi = 10.1002/14651858.CD007368.pub2 }}</ref> There is insufficient evidence for ].<ref name=Chang2014/> There is no strong evidence to recommend that children who have non-measles related pneumonia take ] supplements.<ref>{{cite journal | vauthors = Ni J, Wei J, Wu T | title = Vitamin A for non-measles pneumonia in children | journal = The Cochrane Database of Systematic Reviews | issue = 3 | pages = CD003700 | date = July 2005 | volume = 2005 | pmid = 16034908 | pmc = 6991929 | doi = 10.1002/14651858.CD003700.pub2 }}</ref> Vitamin D, as of 2023, is of unclear benefit in children.<ref>{{cite journal |last1=Das |first1=Rashmi R. |last2=Singh |first2=Meenu |last3=Naik |first3=Sushree S. |date=2023-01-12 |title=Vitamin D as an adjunct to antibiotics for the treatment of acute childhood pneumonia |journal=The Cochrane Database of Systematic Reviews |volume=1 |issue=1 |pages=CD011597 |doi=10.1002/14651858.CD011597.pub3 |issn=1469-493X |pmc=9835443 |pmid=36633175 }}</ref> Vitamin C administration in pneumonia needs further research, although it can be given to patient of low plasma vitamin C because it is not expensive and low risk.<ref name=":0" />

Pneumonia can cause severe illness in a number of ways, and pneumonia with evidence of organ dysfunction may require ] admission for observation and specific treatment.<ref name=Phua>{{cite journal | vauthors = Phua J, Dean NC, Guo Q, Kuan WS, Lim HF, Lim TK | title = Severe community-acquired pneumonia: timely management measures in the first 24 hours | journal = Critical Care | volume = 20 | issue = 1 | page = 237 | date = August 2016 | pmid = 27567896 | pmc = 5002335 | doi = 10.1186/s13054-016-1414-2 | doi-access = free }}</ref> The main impact is on the respiratory and the circulatory system. ] not responding to normal oxygen therapy may require ] delivered through nasal cannulae,<ref name=Phua/> ],<ref>{{cite journal |vauthors=Zhang Y, Fang C, Dong BR, Wu T, Deng JL |date=March 2012 |editor1-last=Dong |editor1-first=Bi Rong |title=Oxygen therapy for pneumonia in adults |url=https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006607.pub4/full |journal=The Cochrane Database of Systematic Reviews |volume=3 |issue=3 |pages=CD006607 |doi=10.1002/14651858.CD006607.pub4 |pmid=22419316}}</ref> or in severe cases mechanical ventilation through an endotracheal tube.<ref name=Phua/> Regarding circulatory problems as part of sepsis, evidence of poor blood flow or low blood pressure is initially treated with 30 mL/kg of ] infused intravenously.<ref name="Elena 2015"/> In situations where fluids alone are ineffective, ] medication may be required.<ref name=Phua/>

For adults with moderate or severe ] (ARDS) undergoing mechanical ventilation, there is a reduction in mortality when people ] for at least 12 hours a day. However, this increases the risk of endotracheal tube obstruction and pressure sores.<ref>{{cite journal |vauthors=Munshi L, Del Sorbo L, Adhikari NK, Hodgson CL, Wunsch H, Meade MO, Uleryk E, Mancebo J, Pesenti A, Ranieri VM, Fan E |date=October 2017 |title=Prone Position for Acute Respiratory Distress Syndrome. A Systematic Review and Meta-Analysis |url=https://www.atsjournals.org/doi/10.1513/AnnalsATS.201704-343OT |journal=Annals of the American Thoracic Society |volume=14 |issue=Supplement_4 |pages=S280–S288 |doi=10.1513/AnnalsATS.201704-343OT |pmid=29068269 |hdl-access=free |s2cid=43367332 |hdl=2434/531962}}</ref>

===Bacterial===
Antibiotics improve outcomes in those with bacterial pneumonia.<ref name=CochraneTx13/> The first dose of antibiotics should be given as soon as possible.<ref name="Elena 2015"/> Increased use of antibiotics, however, may lead to the development of ] strains of bacteria.<ref name=Pak2014>{{cite journal | vauthors = Pakhale S, Mulpuru S, Verheij TJ, Kochen MM, Rohde GG, Bjerre LM | title = Antibiotics for community-acquired pneumonia in adult outpatients | journal = The Cochrane Database of Systematic Reviews | issue = 10 | pages = CD002109 | date = October 2014 | volume = 2014 | pmid = 25300166 | pmc = 7078574 | doi = 10.1002/14651858.CD002109.pub4 }}</ref> Antibiotic choice depends initially on the characteristics of the person affected, such as age, underlying health, and the location the infection was acquired. Antibiotic use is also associated with side effects such as nausea, diarrhea, dizziness, taste distortion, or headaches.<ref name=Pak2014/> In the UK, ] with ] is recommended as the first line for community-acquired pneumonia, with ] or ] as alternatives.<ref name=BTS09/> In North America, amoxicillin, doxycycline, and in some areas a macrolide (such as ] or ]) is the first-line outpatient treatment in adults.<ref name=EOP10/><ref name=Lutfiyya>{{cite journal | vauthors = Lutfiyya MN, Henley E, Chang LF, Reyburn SW | title = Diagnosis and treatment of community-acquired pneumonia | journal = American Family Physician | volume = 73 | issue = 3 | pages = 442–50 | date = February 2006 | pmid = 16477891 | url = http://www.aafp.org/afp/2006/0201/p442.pdf | url-status = live | archive-url = https://web.archive.org/web/20120409042309/http://www.aafp.org/afp/2006/0201/p442.pdf | archive-date = 9 April 2012 }}</ref><ref name=Met2019/> In children with mild or moderate symptoms, amoxicillin taken by mouth is the first line.<ref name=PIDS11/><ref>{{cite web|url=https://www.who.int/mediacentre/factsheets/fs331/en/|title=Pneumonia Fact Sheet|date=September 2016|website=World Health Organization|language=en-GB|access-date=14 January 2018}}</ref><ref>{{cite journal | vauthors = Lodha R, Kabra SK, Pandey RM | title = Antibiotics for community-acquired pneumonia in children | journal = The Cochrane Database of Systematic Reviews | issue = 6 | pages = CD004874 | date = June 2013 | volume = 2013 | pmid = 23733365 | pmc = 7017636 | doi = 10.1002/14651858.CD004874.pub4 }}</ref> The use of ] in uncomplicated cases is discouraged due to concerns about side-effects and generating resistance in light of there being no greater benefit.<ref name=EOP10/><ref>{{cite journal | vauthors = Eliakim-Raz N, Robenshtok E, Shefet D, Gafter-Gvili A, Vidal L, Paul M, Leibovici L | title = Empiric antibiotic coverage of atypical pathogens for community-acquired pneumonia in hospitalized adults | journal = The Cochrane Database of Systematic Reviews | volume = 9 | issue = 9 | pages = CD004418 | date = September 2012 | pmid = 22972070 | pmc = 7017099 | doi = 10.1002/14651858.CD004418.pub4 | editor1-last = Eliakim-Raz | editor1-first = Noa }}</ref>

For those who require hospitalization and caught their pneumonia in the community the use of a β-lactam such as ] plus a macrolide such as azithromycin is recommended.<ref>{{cite journal |vauthors=Lee JS, Giesler DL, Gellad WF, Fine MJ |date=February 2016 |title=Antibiotic Therapy for Adults Hospitalized With Community-Acquired Pneumonia: A Systematic Review |url=https://jamanetwork.com/journals/jama/article-abstract/2488313 |journal=JAMA |volume=315 |issue=6 |pages=593–602 |doi=10.1001/jama.2016.0115 |pmid=26864413}}</ref><ref name=Met2019/> A ] may replace azithromycin but is less preferred.<ref name=Met2019/> Antibiotics by mouth and by injection appear to be similarly effective in children with severe pneumonia.<ref name=Roj2006>{{cite journal | vauthors = Rojas MX, Granados C | title = Oral antibiotics versus parenteral antibiotics for severe pneumonia in children | journal = The Cochrane Database of Systematic Reviews | issue = 2 | pages = CD004979 | date = April 2006 | volume = 2006 | pmid = 16625618 | pmc = 6885030 | doi = 10.1002/14651858.CD004979.pub2 }}</ref>

The duration of treatment has traditionally been seven to ten days, but increasing evidence suggests that shorter courses (3–5 days) may be effective for certain types of pneumonia and may reduce the risk of antibiotic resistance.<ref>{{cite journal | vauthors = Tansarli GS, Mylonakis E | title = Systematic Review and Meta-analysis of the Efficacy of Short-Course Antibiotic Treatments for Community-Acquired Pneumonia in Adults | journal = Antimicrobial Agents and Chemotherapy | volume = 62 | issue = 9 | date = September 2018 | pmid = 29987137 | pmc = 6125522 | doi = 10.1128/AAC.00635-18 }}</ref><ref>{{cite journal | vauthors = Scalera NM, File TM | title = How long should we treat community-acquired pneumonia? | journal = Current Opinion in Infectious Diseases | volume = 20 | issue = 2 | pages = 177–81 | date = April 2007 | pmid = 17496577 | doi = 10.1097/QCO.0b013e3280555072 | s2cid = 21502165 }}</ref><ref name=Pug2015>{{cite journal | vauthors = Pugh R, Grant C, Cooke RP, Dempsey G | title = Short-course versus prolonged-course antibiotic therapy for hospital-acquired pneumonia in critically ill adults | journal = The Cochrane Database of Systematic Reviews | issue = 8 | pages = CD007577 | date = August 2015 | volume = 2015 | pmid = 26301604 | pmc = 7025798 | doi = 10.1002/14651858.CD007577.pub3 }}</ref><ref>{{cite journal | vauthors = Haider BA, Saeed MA, Bhutta ZA | title = Short-course versus long-course antibiotic therapy for non-severe community-acquired pneumonia in children aged 2 months to 59 months | journal = The Cochrane Database of Systematic Reviews | issue = 2 | pages = CD005976 | date = April 2008 | pmid = 18425930 | doi = 10.1002/14651858.CD005976.pub2 | url = https://ecommons.aku.edu/cgi/viewcontent.cgi?article=1134&context=pakistan_fhs_mc_women_childhealth_paediatr }}</ref> Research in children showed that a shorter, 3-day course of amoxicillin was as effective as a longer, 7-day course for treating pneumonia in this population.<ref>{{cite journal |date=27 May 2022 |title=3 days' antibiotic is effective in childhood pneumonia |url=https://evidence.nihr.ac.uk/alert/short-course-antibiotics-effective-in-childhood-pneumonia/ |access-date=8 June 2022 |website=NIHR Evidence |doi=10.3310/nihrevidence_50885 |s2cid=249937345 |language=en-GB}}</ref><ref>{{cite journal |last1=Barratt |first1=Sam |last2=Bielicki |first2=Julia A. |last3=Dunn |first3=David |last4=Faust |first4=Saul N. |last5=Finn |first5=Adam |last6=Harper |first6=Lynda |last7=Jackson |first7=Pauline |last8=Lyttle |first8=Mark D. |last9=Powell |first9=Colin VE |last10=Rogers |first10=Louise |last11=Roland |first11=Damian |date=4 November 2021 |title=Amoxicillin duration and dose for community-acquired pneumonia in children: the CAP-IT factorial non-inferiority RCT |url=https://www.journalslibrary.nihr.ac.uk/hta/hta25600/ |journal=Health Technology Assessment |language=EN |volume=25 |issue=60 |pages=1–72 |doi=10.3310/hta25600 |pmid=34738518 |s2cid=243762087 |issn=2046-4924|doi-access=free }}</ref> For pneumonia that is associated with a ventilator caused by non-fermenting Gram-negative bacilli (NF-GNB), a shorter course of antibiotics increases the risk that the pneumonia will return.<ref name=Pug2015/> Recommendations for hospital-acquired pneumonia include third- and fourth-generation ], ]s, fluoroquinolones, ]s, and ].<ref name=ATS2005/> These antibiotics are often given ] and used in combination.<ref name=ATS2005/> In those treated in hospital, more than 90% improve with the initial antibiotics.<ref name=M32/> For people with ventilator-acquired pneumonia, the choice of antibiotic therapy will depend on the person's risk of being infected with a strain of bacteria that is ].<ref name=Ar2016/> Once clinically stable, intravenous antibiotics should be switched to oral antibiotics.<ref name="Elena 2015"/> For those with '']'' (MRSA) or ''Legionella'' infections, prolonged antibiotics may be beneficial.<ref name="Elena 2015"/>

The addition of ]s to standard antibiotic treatment appears to improve outcomes, reducing death and morbidity for adults with severe community acquired pneumonia, and reducing death for adults and children with non-severe community acquired pneumonia.<ref name=Stern2017>{{cite journal | vauthors = Stern A, Skalsky K, Avni T, Carrara E, Leibovici L, Paul M | title = Corticosteroids for pneumonia | journal = The Cochrane Database of Systematic Reviews | volume = 2017 | pages = CD007720 | date = December 2017 | issue = 12 | pmid = 29236286 | pmc = 6486210 | doi = 10.1002/14651858.CD007720.pub3 }}</ref><ref>{{cite journal |vauthors=Wu WF, Fang Q, He GJ |date=February 2018 |title=Efficacy of corticosteroid treatment for severe community-acquired pneumonia: A meta-analysis |url=https://www.sciencedirect.com/science/article/abs/pii/S0735675717305776 |journal=The American Journal of Emergency Medicine |volume=36 |issue=2 |pages=179–84 |doi=10.1016/j.ajem.2017.07.050 |pmid=28756034 |s2cid=3274763}}</ref> A 2017 review therefore recommended them in adults with severe community acquired pneumonia.<ref name=Stern2017 /> A 2019 guideline however recommended against their general use, unless refractory shock was present.<ref name=Met2019/> Side effects associated with the use of corticosteroids include high blood sugar.<ref name=Stern2017 /> There is some evidence that adding corticosteroids to the standard PCP pneumonia treatment may be beneficial for people who are infected with HIV.<ref name=Ewa2015/>

The use of granulocyte colony stimulating factor (G-CSF) along with antibiotics does not appear to reduce mortality and routine use for treating pneumonia is not supported by evidence.<ref>{{cite journal |vauthors=Cheng AC, Stephens DP, Currie BJ |date=April 2007 |title=Granulocyte-colony stimulating factor (G-CSF) as an adjunct to antibiotics in the treatment of pneumonia in adults |url=https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004400.pub3/full |journal=The Cochrane Database of Systematic Reviews |issue=2 |pages=CD004400 |doi=10.1002/14651858.CD004400.pub3 |pmid=17443546}}</ref>

===Viral===
] may be used to treat ] caused by influenza viruses (] and ]).<ref name=Lancet11/> No specific ] medications are recommended for other types of community acquired viral pneumonias including ], adenovirus, ], and parainfluenza virus.<ref name=Lancet11/> Influenza A may be treated with rimantadine or amantadine, while influenza A or B may be treated with oseltamivir, zanamivir or ].<ref name=Lancet11/> These are of most benefit if they are started within 48 hours of the onset of symptoms.<ref name=Lancet11/> Many strains of ] influenza A, also known as ] or "bird flu", have shown resistance to rimantadine and amantadine.<ref name=Lancet11/> The use of antibiotics in viral pneumonia is recommended by some experts, as it is impossible to rule out a complicating bacterial infection.<ref name=Lancet11/> The ] recommends that antibiotics be withheld in those with mild disease.<ref name=Lancet11/> The use of corticosteroids is controversial.<ref name=Lancet11/>

===Aspiration===
In general, ] is treated conservatively with antibiotics indicated only for aspiration pneumonia.<ref name="PA2011">{{cite journal |vauthors=Marik PE |date=May 2011 |title=Pulmonary aspiration syndromes |url=https://journals.lww.com/co-pulmonarymedicine/Abstract/2011/05000/Pulmonary_aspiration_syndromes.5.aspx |journal=Current Opinion in Pulmonary Medicine |volume=17 |issue=3 |pages=148–54 |doi=10.1097/MCP.0b013e32834397d6 |pmid=21311332 |s2cid=31735383}}</ref> The choice of antibiotic will depend on several factors, including the suspected causative organism and whether pneumonia was acquired in the community or developed in a hospital setting. Common options include ], a combination of a ] and ], or an aminoglycoside.<ref name=OConnor>
{{cite journal|author=O'Connor S |title=Aspiration pneumonia and pneumonitis |journal=Australian Prescriber |volume=26 |issue=1 |year=2003 |pages=14–17 |doi=10.18773/austprescr.2003.009 |doi-access=free }}</ref>
Corticosteroids are sometimes used in aspiration pneumonia, but there is limited evidence to support their effectiveness.<ref name=PA2011/>

===Follow-up===
The British Thoracic Society recommends that a follow-up chest radiograph be taken in people with persistent symptoms, smokers, and people older than 50.<ref name=BTS09/> American guidelines vary, from generally recommending a follow-up chest radiograph<ref>{{cite journal | vauthors = Ramsdell J, Narsavage GL, Fink JB | title = Management of community-acquired pneumonia in the home: an American College of Chest Physicians clinical position statement | journal = Chest | volume = 127 | issue = 5 | pages = 1752–63 | date = May 2005 | pmid = 15888856 | doi = 10.1378/chest.127.5.1752 }}</ref> to not mentioning any follow-up.<ref name=IDSA2007/>

==Prognosis==
With treatment, most types of bacterial pneumonia will stabilize in 3–6&nbsp;days.<ref name=Behera2010>{{cite book|vauthors=Behera D|title=Textbook of pulmonary medicine|year=2010|publisher=Jaypee Brothers Medical Pub.|location=New Delhi|isbn=978-81-8448-749-7|pages=296–97|url=https://books.google.com/books?id=0TbJjd9eTp0C&pg=PA296|edition=2nd}}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> It often takes a few weeks before most symptoms resolve.<ref name=Behera2010/> X-ray findings typically clear within four weeks and mortality is low (less than 1%).<ref name=Clinic2011/><ref name=C6/> In the elderly or people with other lung problems, recovery may take more than 12&nbsp;weeks.<!--<ref name=Clinic2011/> --> In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%.<ref name=Clinic2011/> Pneumonia is the most common ] that causes death.<ref name=M32>Murray and Nadel (2010). Chapter 32.</ref> Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized.<ref name=EBMED05/> However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis.<ref name="Elena 2015"/> If pneumonia deteriorates after 72 hours, it could be due to nosocomial infection or excerbation of other underlying comorbidities.<ref name="Elena 2015"/> About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurological disorders, or due to new onset of pneumonia.<ref name="Elena 2015"/>

Complications may occur in particular in the elderly and those with underlying health problems.<ref name=C6/> This may include, among others: ], lung abscess, ], acute respiratory distress syndrome, sepsis, and worsening of underlying health problems.<ref name=C6>Cunha (2010). pp. 6–18.</ref>

===Clinical prediction rules===
Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia.<ref name=M32/> These rules are often used to decide whether to hospitalize the person.<ref name=M32/>
* ] score, which takes into account the severity of symptoms, any underlying diseases, and age<ref>{{cite journal | vauthors = Rello J | title = Demographics, guidelines, and clinical experience in severe community-acquired pneumonia | journal = Critical Care | volume = 12 | issue = Suppl 6 | pages = S2 | year = 2008 | pmid = 19105795 | pmc = 2607112 | doi = 10.1186/cc7025 | doi-access = free }}</ref>
* ] (or ''PSI Score'')<ref name=M32/>

===Pleural effusion, empyema, and abscess===
]: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung.]]

In pneumonia, a collection of fluid may form in the ].<ref name=Yu2011>{{cite journal | vauthors = Yu H | title = Management of pleural effusion, empyema, and lung abscess | journal = Seminars in Interventional Radiology | volume = 28 | issue = 1 | pages = 75–86 | date = March 2011 | pmid = 22379278 | pmc = 3140254 | doi = 10.1055/s-0031-1273942 }}</ref> Occasionally, microorganisms will infect this fluid, causing an ].<ref name=Yu2011/> To distinguish an empyema from the more common simple ], the fluid may be collected with a needle (]), and examined.<ref name=Yu2011/> If this shows evidence of empyema, complete drainage of the fluid is necessary, often requiring a ].<ref name=Yu2011/> In severe cases of empyema, ] may be needed.<ref name=Yu2011/> If the infected fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity. If the fluid is sterile, it must be drained only if it is causing symptoms or remains unresolved.<ref name=Yu2011/>

In rare circumstances, bacteria in the lung will form a pocket of infected fluid called a lung abscess.<ref name=Yu2011/> Lung abscesses can usually be seen with a chest X-ray but frequently require a chest CT scan to confirm the diagnosis.<ref name=Yu2011/> Abscesses typically occur in aspiration pneumonia, and often contain several types of bacteria. Long-term antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a surgeon or ].<ref name=Yu2011/>

===Respiratory and circulatory failure===
Pneumonia can cause respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response.<!--<ref name=M31/> --> The lungs quickly fill with fluid and become stiff.<!--<ref name=M31/> --> This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, may require long periods of mechanical ventilation for survival.<ref name=M31/> Other causes of circulatory failure are ], inflammation, and increased coagulability.<ref name="Elena 2015"/>

Sepsis is a potential complication of pneumonia but usually occurs in people with poor immunity or ].<!--<ref name=C250/> --> The organisms most commonly involved are ''Streptococcus pneumoniae'', ''Haemophilus influenzae'', and ''Klebsiella pneumoniae''.<!--<ref name=C250/> --> Other causes of the symptoms should be considered such as a ] or a pulmonary embolism.<ref name=C250>Cunha (2010). pp. 250–51.</ref>


==Epidemiology== ==Epidemiology==
{{Main|Epidemiology of pneumonia}}
Pneumonia is a common illness in all parts of the world. It is a major cause of death among all age groups. In children, the majority of deaths occur in the newborn period, with over two million deaths a year worldwide. The ] estimates that one in three newborn infant deaths are due to pneumonia.<ref name=garenne>Garenne M, Ronsmans C, Campbell H. The magnitude of mortality from acute respiratory infections in children under 5 years in developing countries.'' World Health Stat Q'' 1992;45:180. PMID 1462653</ref> Mortality from pneumonia generally decreases with age until late adulthood. Elderly individuals, however, are at particular risk for pneumonia and associated mortality.
]
] for lower respiratory infections per 100,000&nbsp;inhabitants in 2004<ref>{{cite web |url=https://www.who.int/entity/healthinfo/statistics/bodgbddeathdalyestimates.xls |title=Mortality and Burden of Disease Estimates for WHO Member States in 2002 |format=xls |work=World Health Organization |year=2002 |url-status=live |archive-url=https://web.archive.org/web/20130116174540/http://www.who.int/healthinfo/statistics/bodgbddeathdalyestimates.xls |archive-date=16 January 2013 }}</ref>{{Div col|small=yes|colwidth=10em}}
{{legend|#b3b3b3|no data}}
{{legend|#ffff65|less than 100}}
{{legend|#fff200|100–700}}
{{legend|#ffdc00|700–1,400}}
{{legend|#ffc600|1,400–2,100}}
{{legend|#ffb000|2,100–2,800}}
{{legend|#ff9a00|2,800–3,500}}
{{legend|#ff8400|3,500–4,200}}
{{legend|#ff6e00|4,200–4,900}}
{{legend|#ff5800|4,900–5,600}}
{{legend|#ff4200|5,600–6,300}}
{{legend|#ff2c00|6,300–7,000}}
{{legend|#cb0000|more than 7,000}}
{{div col end}}]]

Pneumonia is a common illness affecting approximately 450&nbsp;million people a year and occurring in all parts of the world.<ref name=Lancet11/> It is a major cause of death among all age groups resulting in 4&nbsp;million deaths (7% of the world's total death) yearly.<ref name=Lancet11/><ref name=CochraneTx13/> Rates are greatest in children less than five, and adults older than 75&nbsp;years.<ref name=Lancet11/> It occurs about five times more frequently in the ] than in the developed world.<ref name=Lancet11/> Viral pneumonia accounts for about 200&nbsp;million cases.<ref name=Lancet11/> In the United States, {{as of|2009|lc=y}}, pneumonia is the 8th leading cause of death.<ref name=Clinic2011>{{cite journal | vauthors = Nair GB, Niederman MS | title = Community-acquired pneumonia: an unfinished battle | journal = The Medical Clinics of North America | volume = 95 | issue = 6 | pages = 1143–61 | date = November 2011 | pmid = 22032432 | pmc = 7127066 | doi = 10.1016/j.mcna.2011.08.007 }}</ref>


===Children===
More cases of pneumonia occur during the winter months than during other times of the year. Pneumonia occurs more commonly in males than females, and more often in Blacks than Caucasians. Individuals with underlying illnesses such as ], ], ], ], ], or ] are at increased risk for pneumonia.<ref name=Almirall>Almirall J, Bolibar I, Balanzo X, Gonzalez CA. Risk factors for community-acquired pneumonia in adults: A population-based case-control study.'' Eur Respir J.'' 1999;13:349. PMID 10065680</ref> These individuals are also more likely to have repeated episodes of pneumonia. People who are hospitalized for any reason are also at high risk for pneumonia.
In 2008, pneumonia occurred in approximately 156&nbsp;million children (151&nbsp;million in the developing world and 5&nbsp;million in the developed world).<ref name=Lancet11/> In 2010, it resulted in 1.3&nbsp;million deaths, or 18% of all deaths in those under five years, of which 95% occurred in the developing world.<ref name=Lancet11/><ref name="Develop11">{{cite journal |vauthors=Singh V, Aneja S |date=March 2011 |title=Pneumonia – management in the developing world |url=https://www.sciencedirect.com/science/article/abs/pii/S1526054210000795 |journal=Paediatric Respiratory Reviews |volume=12 |issue=1 |pages=52–59 |doi=10.1016/j.prrv.2010.09.011 |pmid=21172676}}</ref><ref>{{cite journal |vauthors=Liu L, Johnson HL, Cousens S, Perin J, Scott S, Lawn JE, Rudan I, Campbell H, Cibulskis R, Li M, Mathers C, Black RE |date=June 2012 |title=Global, regional, and national causes of child mortality: an updated systematic analysis for 2010 with time trends since 2000 |url=https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60560-1/fulltext |journal=Lancet |volume=379 |issue=9832 |pages=2151–61 |doi=10.1016/S0140-6736(12)60560-1 |pmid=22579125 |s2cid=43866899}}</ref> Countries with the greatest burden of disease include India (43&nbsp;million), China (21&nbsp;million) and Pakistan (10&nbsp;million).<ref>{{cite journal | vauthors = Rudan I, Boschi-Pinto C, Biloglav Z, Mulholland K, Campbell H | title = Epidemiology and etiology of childhood pneumonia | journal = Bulletin of the World Health Organization | volume = 86 | issue = 5 | pages = 408–16 | date = May 2008 | pmid = 18545744 | pmc = 2647437 | doi = 10.2471/BLT.07.048769 | doi-broken-date = 5 December 2024 }}</ref> It is the leading cause of death among children in ].<ref name=Lancet11/><ref name=CochraneTx13/> Many of these deaths occur in the ] period. The World Health Organization estimates that one in three newborn infant deaths is due to pneumonia.<ref name="garenne">{{cite journal |vauthors=Garenne M, Ronsmans C, Campbell H |year=1992 |title=The magnitude of mortality from acute respiratory infections in children under 5 years in developing countries |journal=World Health Statistics Quarterly |volume=45 |issue=2–3 |pages=180–91 |pmid=1462653}}</ref> Approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available.<ref>{{cite journal |date=June 1999 |title=Pneumococcal vaccines. WHO position paper |journal=Relevé Épidémiologique Hebdomadaire |volume=74 |issue=23 |pages=177–83 |pmid=10437429}}</ref> The ] has recommended that children and infants with symptoms of CAP should be hospitalized so they have access to pediatric nursing care.<ref>{{cite web |title=Community-Acquired Pneumonia in Infants and Children |url=https://www.idsociety.org/practice-guideline/community-acquired-pneumonia-cap-in-infants-and-children/ |access-date=16 January 2023 |website=www.idsociety.org |language=en}}</ref> In 2011, pneumonia was the most common reason for admission to the hospital after an emergency department visit in the U.S. for infants and children.<ref>{{cite journal | vauthors = Weiss AJ, Wier LM, Stocks C, Blanchard J | title = Overview of Emergency Department Visits in the United States, 2011 | journal = HCUP Statistical Brief No. 174 | publisher = Agency for Healthcare Research and Quality | location = Rockville, MD | date = June 2014 | pmid = 25144109 | url = https://www.hcup-us.ahrq.gov/reports/statbriefs/sb174-Emergency-Department-Visits-Overview.jsp | url-status=live | archive-url = https://web.archive.org/web/20140803154735/http://www.hcup-us.ahrq.gov/reports/statbriefs/sb174-Emergency-Department-Visits-Overview.jsp | archive-date = 3 August 2014 }}</ref>


==History== ==History==
] poster, 1936/1937]]
], the ancient Greek physician known as the "father of medicine."]]
The symptoms of pneumonia were described by ] (c. 460 BC–380 BC):
<blockquote>''Peripneumonia, and pleuritic affections, are to be thus observed: If the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... When pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand''.<ref name=hippo>Hippocrates ''On Acute Diseases'' </ref></blockquote>


However, Hippocrates himself referred to pneumonia as a disease "named by the ancients." He also reported the results of surgical drainage of empyemas. ] (1138–1204 AD) observed "The basic symptoms which occur in pneumonia and which are never lacking are as follows: acute fever, sticking pain in the side, short rapid breaths, ] and cough."<ref name=maimo>Maimonides, ''Fusul Musa'' ("''Pirkei Moshe''").</ref> This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the ] into the 19th century. Pneumonia has been a common disease throughout human history.<ref name=History03>{{cite book |last=Feigin |first=Ralph |title=Textbook of Pediatric Infectious Diseases |year=2004 |publisher=] |location=Philadelphia |isbn=978-0-7216-9329-3 |page=299 |edition=5th |url=https://books.google.com/books?id=G6k0tpPMRsIC&pg=PA299}}</ref> The word is from Greek πνεύμων (pneúmōn) meaning "lung".<ref>{{cite book|last1=Stevenson|first1=Angus |title=Oxford Dictionary of English|date=2010|publisher=OUP Oxford|isbn=978-0-19-957112-3|page=1369|url=https://books.google.com/books?id=anecAQAAQBAJ&pg=PA1369|language=en}}</ref> The symptoms were described by ] ({{circa|460}}–370 BC):<ref name=History03/> "Peripneumonia, and pleuritic affections, are to be thus observed: If the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... When pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand."<ref name="hippo">{{cite book |last=Hippocrates |url=https://en.wikisource.org/On_Regimen_in_Acute_Diseases |title=On acute diseases}}</ref> However, Hippocrates referred to pneumonia as a disease "named by the ancients". He also reported the results of surgical drainage of empyemas. ] (1135–1204 AD) observed: "The basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking ] pain in the side, short rapid breaths, serrated ] and cough."<ref name=maimo>Maimonides, ''Fusul Musa'' ("''Pirkei Moshe''").</ref> This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the ] into the 19th century.


Bacteria were first seen in the airways of individuals who died from pneumonia by ] in 1875.<ref name=klebs>Klebs E. Beiträge zur Kenntniss der pathogenen Schistomyceten. VII Die Monadinen. ''Arch. exptl. Pathol. Parmakol.'' 1875 Dec 10;4(5/6):40–488.</ref> Initial work identifying the two common bacterial causes ''Streptococcus pneumoniae'' and ''Klebsiella pneumoniae'' was performed by ]<ref name=fried>Friedländer C. Über die Schizomyceten bei der acuten fibrösen Pneumonie.'' Virchow's Arch pathol. Anat. u. Physiol.'' 1882 Feb 4;87(2):319–324.</ref> and ]<ref name=fraenkel>Fraenkel A. Über die genuine Pneumonie, Verhandlungen des Congress für innere Medicin. ''Dritter Congress''. 1884 April 21;3:17–31.</ref> in 1882 and 1884, respectively. Friedländer's initial work introduced the ], a fundamental laboratory test still used to identify and categorize bacteria. ]'s paper describing the procedure in 1884 helped differentiate the two different bacteria and showed that pneumonia could be caused by more than one microorganism.<ref name=gram>Gram C. Über die isolierte Färbung der Schizomyceten in Schnitt- und Trocken-präparaten.'' Fortschr. Med''. 1884 March 15;2(6):185–189.</ref> ] was the first to observe bacteria in the airways of persons having died of pneumonia in 1875.<ref name=klebs>{{cite journal |author=Klebs E |title=''Beiträge zur Kenntniss der pathogenen Schistomyceten''. VII ''Die Monadinen'' |trans-title=Signs for Recognition of the Pathogen Schistomyceten |journal=Arch. Exp. Pathol. Pharmakol. |volume=4 |issue=5/6 |pages=40–88 |date=10 December 1875}}</ref> Initial work identifying the two common bacterial causes, ''Streptococcus pneumoniae'' and ''Klebsiella pneumoniae'', was performed by ]<ref name=fried>{{cite journal |author=Friedländer C |title=''Über die Schizomyceten bei der acuten fibrösen Pneumonie'' |journal=Archiv für Pathologische Anatomie und Physiologie und für Klinische Medicin |volume=87 |issue=2 |pages=319–24 |date=4 February 1882 |doi=10.1007/BF01880516|s2cid=28324193 |url=https://zenodo.org/record/2209659 }}</ref> and ]<ref name=fraenkel>{{cite journal |author=Fraenkel A |title=''Über die genuine Pneumonie, Verhandlungen des Congress für innere Medicin'' |journal=Dritter Congress |volume=3 |pages=17–31 |date=21 April 1884}}</ref> in 1882 and 1884, respectively. Friedländer's initial work introduced the ], a fundamental laboratory test still used today to identify and categorize bacteria. ]'s paper describing the procedure in 1884 helped to differentiate the two bacteria, and showed that pneumonia could be caused by more than one microorganism.<ref name=gram>{{cite journal |author=Gram C |title=''Über die isolierte Färbung der Schizomyceten in Schnitt- und Trocken-präparaten'' |journal=Fortschr. Med. |volume=2 |issue=6 |pages=185–89 |date=15 March 1884}}</ref> In 1887, Jaccond demonstrated pneumonia may be caused by opportunistic bacteria always present in the lung.<ref>{{cite book|url=https://books.google.com/books?id=moM9AQAAIAAJ|title=Scientific American|date=24 September 1887|publisher=Munn & Company|page=196|language=en}}</ref>


Sir ], known as "the father of modern medicine", appreciated the death and disability caused by pneumonia, describing it as the "captain of the men of death" in 1918, as it had overtaken tuberculosis as one of the leading causes of death at the time. This phrase was originally coined by ] in reference to "consumption" (tuberculosis).<ref>{{cite book| veditors = Tomashefski Jr JF |title=Dail and Hammar's pulmonary pathology|year=2008|publisher=Springer|location=New York|isbn=978-0-387-98395-0|page=228|url=https://books.google.com/books?id=j-eYLc1BA3oC&pg=PA228|edition=3rd|display-authors=etal}}</ref><ref>{{cite book | first1 = William | last1 = Osler | first2 = Thomas | last2 = McCrae | title = The principles and practice of medicine: designed for the use of practitioners and students of medicine | url = https://archive.org/details/principlesandpr00mccrgoog |publisher=D. Appleton |year=1920 |page= |edition=9th|quote=<!-- quote=Captain of the Men of Death. --> One of the most widespread and fatal of all acute diseases, pneumonia has become the "Captain of the Men of Death", to use the phrase applied by John Bunyan to consumption.]}}</ref> Osler also described pneumonia as "the old man's friend" as death was often quick and painless when there were much slower and more painful ways to die.<ref name=EBMED05/>
Sir ], known as "the father of modern medicine," appreciated the morbidity and mortality of pneumonia, describing it as the "captain of the men of death" in 1918. However, several key developments in the 1900s improved the outcome for those with pneumonia. With the advent of ] and other antibiotics, modern surgical techniques, and intensive care in the ], mortality from pneumonia dropped precipitously in the developed world. Vaccination of infants against '']'' type b began in 1988 and led to a dramatic decline in cases shortly thereafter.<ref name=adams>Adams WG, Deaver KA, Cochi SL, et al. Decline of childhood Haemophilus influenzae type b (Hib) disease in the Hib vaccine era.'' JAMA'' 1993;269:221-6. PMID 8417239</ref> Vaccination against ''Streptococcus pneumoniae'' in adults began in 1977 and in children began in 2000, resulting in a similar decline.<ref name=whit>Whitney CG, Farley MM, Hadler J, et al. Decline in invasive pneumococcal disease after the introduction of pneumococcal protein-polysaccharide conjugate vaccine.'' New Engl J Med''. 2003;348:1737–1746. PMID 12724479</ref>


Viral pneumonia was first described by ] in 1938. Reimann, Chairman of the Department of Medicine at ], had established the practice of routinely typing the pneumococcal organism in cases where pneumonia presented. Out of this work, the distinction between viral and bacterial strains was noticed.<ref>{{cite web|url=https://jdc.jefferson.edu/cgi/viewcontent.cgi?article=1009&context=wagner2|title=Thomas Jefferson University: Tradition and Heritage|last=Hodges|first=John H|date=1989|editor-last=Wagner|editor-first=Frederick B|website=Jefferson Digital Commons|series=Part III, Chapter 9: Department of Medicine|page=253|publication-date=1989}}</ref>
==See also==
* ]


Several developments in the 1900s improved the outcome for those with pneumonia. With the advent of ] and other antibiotics, modern surgical techniques, and intensive care in the 20th century, mortality from pneumonia, which had approached 30%, dropped precipitously in the developed world. Vaccination of infants against ''Haemophilus influenzae'' type B began in 1988 and led to a dramatic decline in cases shortly thereafter.<ref name=adams>{{cite journal | vauthors = Adams WG, Deaver KA, Cochi SL, Plikaytis BD, Zell ER, Broome CV, Wenger JD | title = Decline of childhood Haemophilus influenzae type b (Hib) disease in the Hib vaccine era | journal = JAMA | volume = 269 | issue = 2 | pages = 221–26 | date = January 1993 | pmid = 8417239 | doi = 10.1001/jama.1993.03500020055031 }}</ref> Vaccination against ''Streptococcus pneumoniae'' in adults began in 1977, and in children in 2000, resulting in a similar decline.<ref name="whit">{{cite journal |vauthors=Whitney CG, Farley MM, Hadler J, Harrison LH, Bennett NM, Lynfield R, Reingold A, Cieslak PR, Pilishvili T, Jackson D, Facklam RR, Jorgensen JH, Schuchat A |date=May 2003 |title=Decline in invasive pneumococcal disease after the introduction of protein-polysaccharide conjugate vaccine |journal=The New England Journal of Medicine |volume=348 |issue=18 |pages=1737–46 |doi=10.1056/NEJMoa022823 |pmid=12724479 |collaboration=Active Bacterial Core Surveillance of the Emerging Infections Program Network|doi-access=free }}</ref>
==Notes==
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==External links== ==Society and culture==
{{see also|List of notable pneumonia cases}}
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===Awareness===
{{featured article}}
Due to the relatively low awareness of the disease, 12 November was declared in 2009 as the annual ], a day for concerned citizens and policy makers to take action against the disease.<ref>{{cite web|title=World Pneumonia Day Official Website|url=http://worldpneumoniaday.org/|publisher=Fiinex|access-date=13 August 2011|archive-url=https://web.archive.org/web/20110902154617/http://worldpneumoniaday.org/|archive-date=2 September 2011}}</ref><ref>{{cite journal | vauthors = Hajjeh R, Whitney CG | title = Call to action on world pneumonia day | journal = Emerging Infectious Diseases | volume = 18 | issue = 11 | pages = 1898–99 | date = November 2012 | pmid = 23092708 | pmc = 3559175 | doi = 10.3201/eid1811.121217 }}</ref>
{{Respiratory pathology}}


===Costs===
]
The global economic cost of community-acquired pneumonia has been estimated at $17&nbsp;billion annually.<ref name=Clinic2011/> Other estimates are considerably higher. In 2012 the estimated aggregate costs of treating pneumonia in the United States were $20&nbsp;billion;<ref>{{cite web|url=http://meps.ahrq.gov/mepsweb/data_stats/tables_compendia_hh_interactive.jsp?_SERVICE=MEPSSocket0&_PROGRAM=MEPSPGM.TC.SAS&File=HCFY2012&Table=HCFY2012_CNDXP_C&_Debug=|title=Household Component Summary Data Tables|url-status=live|archive-url=https://web.archive.org/web/20170220165205/https://meps.ahrq.gov/mepsweb/data_stats/tables_compendia_hh_interactive.jsp?_SERVICE=MEPSSocket0&_PROGRAM=MEPSPGM.TC.SAS&File=HCFY2012&Table=HCFY2012_CNDXP_C&_Debug=|archive-date=20 February 2017}}</ref> the median cost of a single pneumonia-related hospitalization is over $15,000.<ref>{{cite web|url=http://meps.ahrq.gov/mepsweb/data_stats/tables_compendia_hh_interactive.jsp?_SERVICE=MEPSSocket0&_PROGRAM=MEPSPGM.TC.SAS&File=HCFY2012&Table=HCFY2012_CNDXP_CA&_Debug=|title=Household Component Summary Data Tables|url-status=live|archive-url=https://web.archive.org/web/20170220165213/https://meps.ahrq.gov/mepsweb/data_stats/tables_compendia_hh_interactive.jsp?_SERVICE=MEPSSocket0&_PROGRAM=MEPSPGM.TC.SAS&File=HCFY2012&Table=HCFY2012_CNDXP_CA&_Debug=|archive-date=20 February 2017}}</ref> According to data released by the ], average 2012 hospital charges for inpatient treatment of uncomplicated pneumonia in the U.S. were $24,549 and ranged as high as $124,000. The average cost of an emergency room consult for pneumonia was $943 and the average cost for medication was $66.<ref>{{cite news |url=https://www.washingtonpost.com/blogs/wonkblog/wp/2013/05/08/one-hospital-charges-8000-another-38000/ |title=One hospital charges $8,000 – another, $38,000 |newspaper=The Washington Post}}</ref> Aggregate annual costs of treating pneumonia in Europe have been estimated at €10&nbsp;billion.<ref>{{cite journal | vauthors = Welte T, Torres A, Nathwani D | title = Clinical and economic burden of community-acquired pneumonia among adults in Europe | journal = Thorax | volume = 67 | issue = 1 | pages = 71–79 | date = January 2012 | pmid = 20729232 | doi = 10.1136/thx.2009.129502 | doi-access = free }}</ref>
]


== References ==
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'''Footnotes'''
{{notelist}}


'''Citations'''
{{Reflist}}


=== Bibliography ===
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{{Refbegin}}
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* {{cite book| veditors = Cunha BA |title=Pneumonia essentials|year=2010|publisher=Physicians' Press|location=Sudbury, MA|isbn=978-0-7637-7220-8|edition=3rd|url=https://books.google.com/books?id=VVgmFAbnrUgC}}
]
* {{cite book| first = John F. | last = Murray |title=Murray and Nadel's textbook of respiratory medicine |year=2010|publisher=Saunders/Elsevier|location=Philadelphia, PA|isbn=978-1-4160-4710-0|edition=5th}}
]
{{Refend}}
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== External links ==
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{{Wikiquote}}
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{{Wiktionary}}
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{{Medical condition classification and resources
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| Curlie = Health/Conditions_and_Diseases/Respiratory_Disorders/Pneumonia/
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| DiseasesDB = 10166
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| ICD11 = {{ICD11|CA40}}, {{ICD11|CA71.0}}, {{ICD11|KB24}}
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| ICD10 = {{ICD10|J10.0}}, {{ICD10|J11.0}} {{ICD10|J12}}, {{ICD10|J13}}, {{ICD10|J14}}, {{ICD10|J15}}, {{ICD10|J16}}, {{ICD10|J17}}, {{ICD10|J18}}, {{ICD10|J69.0}}, {{ICD10|P23}}
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| ICD9 = {{ICD9|480}}-{{ICD9|486}}, {{ICD9|770.0}}
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| MedlinePlus = 000145
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| eMedicineSubj = search
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| eMedicineTopic = pneumonia
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| MeshID = D011014
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| Scholia = Q12192
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| SNOMED CT = 233604007
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}}
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{{Pneumonia}}
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{{Respiratory pathology}}
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{{Authority control}}
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Latest revision as of 01:28, 22 December 2024

Inflammation of the alveoli of the lungs

Not to be confused with Pneumonitis. For other uses, see Pneumonia (disambiguation).

Medical condition
Pneumonia
Other namesPneumonitis
Chest X-ray of a pneumonia caused by influenza and Haemophilus influenzae, with patchy consolidations, mainly in the right upper lobe (arrow)
Pronunciation
SpecialtyPulmonology, infectious disease
SymptomsCough, shortness of breath, chest pain, fever
DurationFew weeks
CausesBacteria, virus, aspiration
Risk factorsCystic fibrosis, COPD, sickle cell disease, asthma, diabetes, heart failure, history of smoking, very young age, older age
Diagnostic methodBased on symptoms, chest X-ray
Differential diagnosisCOPD, asthma, pulmonary edema, pulmonary embolism
PreventionVaccines, handwashing, not smoking
MedicationAntibiotics, antivirals, oxygen therapy
Frequency450 million (7%) per year
DeathsFour million per year

Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity of the condition is variable.

Pneumonia is usually caused by infection with viruses or bacteria, and less commonly by other microorganisms. Identifying the responsible pathogen can be difficult. Diagnosis is often based on symptoms and physical examination. Chest X-rays, blood tests, and culture of the sputum may help confirm the diagnosis. The disease may be classified by where it was acquired, such as community- or hospital-acquired or healthcare-associated pneumonia.

Risk factors for pneumonia include cystic fibrosis, chronic obstructive pulmonary disease (COPD), sickle cell disease, asthma, diabetes, heart failure, a history of smoking, a poor ability to cough (such as following a stroke), and immunodeficiency.

Vaccines to prevent certain types of pneumonia (such as those caused by Streptococcus pneumoniae bacteria, influenza viruses, or SARS-CoV-2) are available. Other methods of prevention include hand washing to prevent infection, prompt treatment of worsening respiratory symptoms, and not smoking.

Treatment depends on the underlying cause. Pneumonia believed to be due to bacteria is treated with antibiotics. If the pneumonia is severe, the affected person is generally hospitalized. Oxygen therapy may be used if oxygen levels are low.

Each year, pneumonia affects about 450 million people globally (7% of the population) and results in about 4 million deaths. With the introduction of antibiotics and vaccines in the 20th century, survival has greatly improved. Nevertheless, pneumonia remains a leading cause of death in developing countries, and also among the very old, the very young, and the chronically ill. Pneumonia often shortens the period of suffering among those already close to death and has thus been called "the old man's friend".

Video summary (script)

Signs and symptoms

A diagram of the human body outlining the key symptoms of pneumonia
Main symptoms of infectious pneumonia

People with infectious pneumonia often have a productive cough, fever accompanied by shaking chills, shortness of breath, sharp or stabbing chest pain during deep breaths, and an increased rate of breathing. In elderly people, confusion may be the most prominent sign.

The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing. Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease, malnutrition or in the elderly. In addition, a cough is frequently absent in children less than 2 months old. More severe signs and symptoms in children may include blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness.

Bacterial and viral cases of pneumonia usually result in similar symptoms. Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by Legionella may occur with abdominal pain, diarrhea, or confusion. Pneumonia caused by Streptococcus pneumoniae is associated with rusty colored sputum. Pneumonia caused by Klebsiella may have bloody sputum often described as "currant jelly". Bloody sputum (known as hemoptysis) may also occur with tuberculosis, Gram-negative pneumonia, lung abscesses and more commonly acute bronchitis. Pneumonia caused by Mycoplasma pneumoniae may occur in association with swelling of the lymph nodes in the neck, joint pain, or a middle ear infection. Viral pneumonia presents more commonly with wheezing than bacterial pneumonia. Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause. However, evidence has not supported this distinction, therefore it is no longer emphasized.

Symptoms frequency
Symptom Frequency
Cough 79–91%
Fatigue 90%
Fever 71–75%
Shortness of breath 67–75%
Sputum 60–65%
Chest pain 39–49%

Cause

Three lone round objects in a black background
The bacterium Streptococcus pneumoniae, a common cause of pneumonia, imaged by an electron microscope

Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although more than 100 strains of infectious agents have been identified, only a few are responsible for the majority of cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults. A causative agent may not be isolated in about half of cases despite careful testing. In an active population-based surveillance for community-acquired pneumonia requiring hospitalization in five hospitals in Chicago and Nashville from January 2010 through June 2012, 2259 patients were identified who had radiographic evidence of pneumonia and specimens that could be tested for the responsible pathogen. Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria. Specifically, 23% had one or more viruses, 11% had one or more bacteria, 3% had both bacterial and viral pathogens, and 1% had a fungal or mycobacterial infection. "The most common pathogens were human rhinovirus (in 9% of patients), influenza virus (in 6%), and Streptococcus pneumoniae (in 5%)."

The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis.

Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, sickle cell disease (SCD), asthma, chronic kidney disease, liver disease, and biological aging. Additional risks in children include not being breastfed, exposure to cigarette smoke and other air pollution, malnutrition, and poverty. The use of acid-suppressing medications – such as proton-pump inhibitors or H2 blockers – is associated with an increased risk of pneumonia. Approximately 10% of people who require mechanical ventilation develop ventilator-associated pneumonia, and people with a gastric feeding tube have an increased risk of developing aspiration pneumonia. Moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia. As with Avanos Medical's feeding tube placement system, the CORTRAK* 2 EAS, which was recalled in May 2022 by the FDA due to adverse events reported, including pneumonia, caused a total of 60 injuries and 23 patient deaths, as communicated by the FDA. For people with certain variants of the FER gene, the risk of death is reduced in sepsis caused by pneumonia. However, for those with TLR6 variants, the risk of getting Legionnaires' disease is increased.

Bacteria

Main article: Bacterial pneumonia
Cavitating pneumonia due to MRSA as seen on a CT scan

Bacteria are the most common cause of community-acquired pneumonia (CAP), with Streptococcus pneumoniae isolated in nearly 50% of cases. Other commonly isolated bacteria include Haemophilus influenzae in 20%, Chlamydophila pneumoniae in 13%, and Mycoplasma pneumoniae in 3% of cases; Staphylococcus aureus; Moraxella catarrhalis; and Legionella pneumophila. A number of drug-resistant versions of the above infections are becoming more common, including drug-resistant Streptococcus pneumoniae (DRSP) and methicillin-resistant Staphylococcus aureus (MRSA).

The spreading of organisms is facilitated by certain risk factors. Alcoholism is associated with Streptococcus pneumoniae, anaerobic organisms, and Mycobacterium tuberculosis; smoking facilitates the effects of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Legionella pneumophila. Exposure to birds is associated with Chlamydia psittaci; farm animals with Coxiella burnetti; aspiration of stomach contents with anaerobic organisms; and cystic fibrosis with Pseudomonas aeruginosa and Staphylococcus aureus. Streptococcus pneumoniae is more common in the winter, and it should be suspected in persons aspirating a large number of anaerobic organisms.

Viruses

Main article: Viral pneumonia
A chest x-ray of a patient with severe viral pneumonia due to SARS

In adults, viruses account for about one third of pneumonia cases, and in children for about 15% of them. Commonly implicated agents include rhinoviruses, coronaviruses, influenza virus, respiratory syncytial virus (RSV), adenovirus, and parainfluenza. Herpes simplex virus rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns. After organ transplantation or in otherwise immunocompromised persons, there are high rates of cytomegalovirus pneumonia. Those with viral infections may be secondarily infected with the bacteria Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae, particularly when other health problems are present. Different viruses predominate at different times of the year; during flu season, for example, influenza may account for more than half of all viral cases. Outbreaks of other viruses also occur occasionally, including hantaviruses and coronaviruses. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can also result in pneumonia.

Fungi

Main article: Fungal pneumonia

Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, immunosuppressive drugs, or other medical problems. It is most often caused by Histoplasma capsulatum, Blastomyces, Cryptococcus neoformans, Pneumocystis jiroveci (pneumocystis pneumonia, or PCP), and Coccidioides immitis. Histoplasmosis is most common in the Mississippi River basin, and coccidioidomycosis is most common in the Southwestern United States. The number of cases of fungal pneumonia has been increasing in the latter half of the 20th century due to increasing travel and rates of immunosuppression in the population. For people infected with HIV/AIDS, PCP is a common opportunistic infection.

Parasites

Main article: Parasitic pneumonia

A variety of parasites can affect the lungs, including Toxoplasma gondii, Strongyloides stercoralis, Ascaris lumbricoides, and Plasmodium malariae. These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector. Except for Paragonimus westermani, most parasites do not specifically affect the lungs but involve the lungs secondarily to other sites. Some parasites, in particular those belonging to the Ascaris and Strongyloides genera, stimulate a strong eosinophilic reaction, which may result in eosinophilic pneumonia. In other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation. In the developed world, these infections are most common in people returning from travel or in immigrants. Around the world, parasitic pneumonia is most common in the immunodeficient.

Noninfectious

Main article: Idiopathic interstitial pneumonia

Idiopathic interstitial pneumonia or noninfectious pneumonia is a class of diffuse lung diseases. They include diffuse alveolar damage, organizing pneumonia, nonspecific interstitial pneumonia, lymphocytic interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and usual interstitial pneumonia. Lipoid pneumonia is another rare cause due to lipids entering the lung. These lipids can either be inhaled or spread to the lungs from elsewhere in the body.

Mechanisms

A schematic diagram of the human lungs with an empty circle on the left representing a normal alveolus and one on the right showing an alveolus full of fluid as in pneumonia
Pneumonia fills the lung's alveoli with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.

Pneumonia frequently starts as an upper respiratory tract infection that moves into the lower respiratory tract. It is a type of pneumonitis (lung inflammation). The normal flora of the upper airway give protection by competing with pathogens for nutrients. In the lower airways, reflexes of the glottis, actions of complement proteins and immunoglobulins are important for protection. Microaspiration of contaminated secretions can infect the lower airways and cause pneumonia. The progress of pneumonia is determined by the virulence of the organism; the amount of organism required to start an infection; and the body's immune response against the infection.

Bacterial

Most bacteria enter the lungs via small aspirations of organisms residing in the throat or nose. Half of normal people have these small aspirations during sleep. While the throat always contains bacteria, potentially infectious ones reside there only at certain times and under certain conditions. A minority of types of bacteria such as Mycobacterium tuberculosis and Legionella pneumophila reach the lungs via contaminated airborne droplets. Bacteria can also spread via the blood. Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the macrophages and neutrophils (defensive white blood cells) attempt to inactivate the bacteria. The neutrophils also release cytokines, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray.

Viral

Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then touch their eyes or nose. Other viral infections occur when contaminated airborne droplets are inhaled through the nose or mouth. Once in the upper airway, the viruses may make their way into the lungs, where they invade the cells lining the airways, alveoli, or lung parenchyma. Some viruses such as measles and herpes simplex may reach the lungs via the blood. The invasion of the lungs may lead to varying degrees of cell death. When the immune system responds to the infection, even more lung damage may occur. Primarily white blood cells, mainly mononuclear cells, generate the inflammation. As well as damaging the lungs, many viruses simultaneously affect other organs and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.

Diagnosis

Crackles Crackles heard in the lungs of a person with pneumonia using a stethoscope.
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Pneumonia is typically diagnosed based on a combination of physical signs and often a chest X-ray. In adults with normal vital signs and a normal lung examination, the diagnosis is unlikely. However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial cause. The overall impression of a physician appears to be at least as good as decision rules for making or excluding the diagnosis.

Diagnosis in children

The World Health Organization has defined pneumonia in children clinically based on either a cough or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness. A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old.

In children, low oxygen levels and lower chest indrawing are more sensitive than hearing chest crackles with a stethoscope or increased respiratory rate. Grunting and nasal flaring may be other useful signs in children less than five years old.

Lack of wheezing is an indicator of Mycoplasma pneumoniae in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not macrolide treatment should be used. The presence of chest pain in children with pneumonia doubles the probability of Mycoplasma pneumoniae.

Diagnosis in adults

In general, in adults, investigations are not needed in mild cases. There is a very low risk of pneumonia if all vital signs and auscultation are normal. C-reactive protein (CRP) may help support the diagnosis. For those with CRP less than 20 mg/L without convincing evidence of pneumonia, antibiotics are not recommended.

Procalcitonin may help determine the cause and support decisions about who should receive antibiotics. Antibiotics are encouraged if the procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L. In people requiring hospitalization, pulse oximetry, chest radiography and blood tests – including a complete blood count, serum electrolytes, C-reactive protein level, and possibly liver function tests – are recommended.

The diagnosis of influenza-like illness can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing. Thus, treatment is frequently based on the presence of influenza in the community or a rapid influenza test.

Adults 65 years old or older, as well as cigarette smokers and people with ongoing medical conditions are at increased risk for pneumonia.

Physical exam

Physical examination may sometimes reveal low blood pressure, high heart rate, or low oxygen saturation. The respiratory rate may be faster than normal, and this may occur a day or two before other signs. Examination of the chest may be normal, but it may show decreased expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchial breathing and are heard on auscultation with a stethoscope. Crackles (rales) may be heard over the affected area during inspiration. Percussion may be dulled over the affected lung, and increased, rather than decreased, vocal resonance distinguishes pneumonia from a pleural effusion.

Imaging

A chest X-ray showing a very prominent wedge-shaped area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia
A black-and-white image shows the internal organs in cross-section as generated by CT. Where one would expect black on the left, one sees a whiter area with black sticks through it.
CT of the chest demonstrating right-sided pneumonia (left side of the image)

A chest radiograph is frequently used in diagnosis. In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain. If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended. Findings do not always match the severity of disease and do not reliably separate between bacterial and viral infection.

X-ray presentations of pneumonia may be classified as lobar pneumonia, bronchopneumonia, lobular pneumonia, and interstitial pneumonia. Bacterial, community-acquired pneumonia classically show lung consolidation of one lung segmental lobe, which is known as lobar pneumonia. However, findings may vary, and other patterns are common in other types of pneumonia. Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side. Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation. Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to interpret in the obese or those with a history of lung disease. Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiographs can increase the diagnostic accuracy of lung consolidation and pleural effusion.

A CT scan can give additional information in indeterminate cases and provide more details in those with an unclear chest radiograph (for example occult pneumonia in chronic obstructive pulmonary disease). They can be used to exclude pulmonary embolism and fungal pneumonia, and detect lung abscesses in those who are not responding to treatments. However, CT scans are more expensive, have a higher dose of radiation, and cannot be done at bedside.

Lung ultrasound may also be useful in helping to make the diagnosis. Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings. It may be more accurate than chest X-ray.

  • Pneumonia seen by ultrasound
  • Pneumonia seen by ultrasound
  • Pneumonia seen by ultrasound Pneumonia seen by ultrasound
  • Right middle lobe pneumonia in a child as seen on plain X-ray Right middle lobe pneumonia in a child as seen on plain X-ray

Microbiology

In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management. For people who do not respond to treatment, sputum culture should be considered, and culture for Mycobacterium tuberculosis should be carried out in persons with a chronic productive cough. Microbiological evaluation is also indicated in severe pneumonia, alcoholism, asplenia, immunosuppression, HIV infection, and those being empirically treated for MRSA of pseudomonas. Although positive blood culture and pleural fluid culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of colonisation of respiratory tract. Testing for other specific organisms may be recommended during outbreaks, for public health reasons. In those hospitalized for severe disease, both sputum and blood cultures are recommended, as well as testing the urine for antigens to Legionella and Streptococcus. Viral infections, can be confirmed via detection of either the virus or its antigens with culture or polymerase chain reaction (PCR), among other techniques. Mycoplasma, Legionella, Streptococcus, and Chlamydia can also be detected using PCR techniques on bronchoalveolar lavage and nasopharyngeal swab. The causative agent is determined in only 15% of cases with routine microbiological tests.

Classification

Main article: Classification of pneumonia

Pneumonitis refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of pulmonary consolidation. Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, healthcare-associated, hospital-acquired, and ventilator-associated pneumonia. It may also be classified by the area of the lung affected: lobar, bronchial pneumonia and acute interstitial pneumonia; or by the causative organism. Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.

The setting in which pneumonia develops is important to treatment, as it correlates to which pathogens are likely suspects, which mechanisms are likely, which antibiotics are likely to work or fail, and which complications can be expected based on the person's health status.

Community

Main article: Community-acquired pneumonia

Community-acquired pneumonia (CAP) is acquired in the community, outside of health care facilities. Compared with healthcare-associated pneumonia, it is less likely to involve multidrug-resistant bacteria. Although the latter are no longer rare in CAP, they are still less likely. Prior stays in healthcare-related environments such as hospitals, nursing homes, or hemodialysis centers or a history of receiving domiciliary care can increase patients' risk for CAP caused by multidrug-resistant bacteria.

Healthcare

Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system, including hospitals, outpatient clinics, nursing homes, dialysis centers, chemotherapy treatment, or home care. HCAP is sometimes called MCAP (medical care–associated pneumonia).

People may become infected with pneumonia in a hospital; this is defined as pneumonia not present at the time of admission (symptoms must start at least 48 hours after admission). It is likely to involve hospital-acquired infections, with higher risk of multidrug-resistant pathogens. People in a hospital often have other medical conditions, which may make them more susceptible to pathogens in the hospital.

Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation. Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after endotracheal intubation.

Differential diagnosis

Several diseases can present with similar signs and symptoms to pneumonia, such as: chronic obstructive pulmonary disease, asthma, pulmonary edema, bronchiectasis, lung cancer, and pulmonary emboli. Unlike pneumonia, asthma and COPD typically present with wheezing, pulmonary edema presents with an abnormal electrocardiogram, cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli present with acute onset sharp chest pain and shortness of breath. Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from acute heart failure. Pulmonary infiltrates that resolved after giving mechanical ventilation should point to heart failure and atelectasis rather than pneumonia. For recurrent pneumonia, underlying lung cancer, metastasis, tuberculosis, a foreign bodies, immunosuppression, and hypersensitivity should be suspected.

Prevention

Prevention includes vaccination, environmental measures, and appropriate treatment of other health problems. It is believed that, if appropriate preventive measures were instituted globally, mortality among children could be reduced by 400,000; and, if proper treatment were universally available, childhood deaths could be decreased by another 600,000.

Vaccination

Vaccination prevents against certain bacterial and viral pneumonias both in children and adults. Influenza vaccines are modestly effective at preventing symptoms of influenza, The Centers for Disease Control and Prevention (CDC) recommends yearly influenza vaccination for every person 6 months and older. Immunizing health care workers decreases the risk of viral pneumonia among their patients.

Vaccinations against Haemophilus influenzae and Streptococcus pneumoniae have good evidence to support their use. There is strong evidence for vaccinating children under the age of 2 against Streptococcus pneumoniae (pneumococcal conjugate vaccine). Vaccinating children against Streptococcus pneumoniae has led to a decreased rate of these infections in adults, because many adults acquire infections from children. A Streptococcus pneumoniae vaccine is available for adults, and has been found to decrease the risk of invasive pneumococcal disease by 74%, but there is insufficient evidence to suggest using the pneumococcal vaccine to prevent pneumonia or death in the general adult population. The CDC recommends that young children and adults over the age of 65 receive the pneumococcal vaccine, as well as older children or younger adults who have an increased risk of getting pneumococcal disease. The pneumococcal vaccine has been shown to reduce the risk of community acquired pneumonia in people with chronic obstructive pulmonary disease, but does not reduce mortality or the risk of hospitalization for people with this condition. People with COPD are recommended by a number of guidelines to have a pneumococcal vaccination. Other vaccines for which there is support for a protective effect against pneumonia include pertussis, varicella, and measles.

Medications

When influenza outbreaks occur, medications such as amantadine or rimantadine may help prevent the condition, but they are associated with side effects. Zanamivir or oseltamivir decrease the chance that people who are exposed to the virus will develop symptoms; however, it is recommended that potential side effects are taken into account.

Other

Smoking cessation and reducing indoor air pollution, such as that from cooking indoors with wood, crop residues or dung, are both recommended. Smoking appears to be the single biggest risk factor for pneumococcal pneumonia in otherwise-healthy adults. Hand hygiene and coughing into one's sleeve may also be effective preventative measures. Wearing surgical masks by the sick may also prevent illness.

Appropriately treating underlying illnesses (such as HIV/AIDS, diabetes mellitus, and malnutrition) can decrease the risk of pneumonia. In children less than 6 months of age, exclusive breast feeding reduces both the risk and severity of disease. In people with HIV/AIDS and a CD4 count of less than 200 cells/uL the antibiotic trimethoprim/sulfamethoxazole decreases the risk of Pneumocystis pneumonia and is also useful for prevention in those that are immunocompromised but do not have HIV.

Testing pregnant women for Group B Streptococcus and Chlamydia trachomatis, and administering antibiotic treatment, if needed, reduces rates of pneumonia in infants; preventive measures for HIV transmission from mother to child may also be efficient. Suctioning the mouth and throat of infants with meconium-stained amniotic fluid has not been found to reduce the rate of aspiration pneumonia and may cause potential harm, thus this practice is not recommended in the majority of situations. In the frail elderly good oral health care may lower the risk of aspiration pneumonia, even though there is no good evidence that one approach to mouth care is better than others in preventing nursing home acquired pneumonia. Zinc supplementation in children 2 months to five years old appears to reduce rates of pneumonia.

For people with low levels of vitamin C in their diet or blood, taking vitamin C supplements may be suggested to decrease the risk of pneumonia, although there is no strong evidence of benefit. There is insufficient evidence to recommend that the general population take vitamin C to prevent or treat pneumonia.

For adults and children in the hospital who require a respirator, there is no strong evidence indicating a difference between heat and moisture exchangers and heated humidifiers for preventing pneumonia. There is tentative evidence that laying flat on the back compared to semi-raised increases pneumonia risks in people who are intubated.

Management

CURB-65
Symptom Points
Confusion 1
Urea>7 mmol/L 1
Respiratory rate>30 1
SBP<90mmHg, DBP<60mmHg 1
Age>=65 1

Antibiotics by mouth, rest, simple analgesics, and fluids usually suffice for complete resolution. However, those with other medical conditions, the elderly, or those with significant trouble breathing may require more advanced care. If the symptoms worsen, the pneumonia does not improve with home treatment, or complications occur, hospitalization may be required. Worldwide, approximately 7–13% of cases in children result in hospitalization, whereas in the developed world between 22 and 42% of adults with community-acquired pneumonia are admitted. The CURB-65 score is useful for determining the need for admission in adults. If the score is 0 or 1, people can typically be managed at home; if it is 2, a short hospital stay or close follow-up is needed; if it is 3–5, hospitalization is recommended. In children those with respiratory distress or oxygen saturations of less than 90% should be hospitalized. The utility of chest physiotherapy in pneumonia has not yet been determined. Over-the-counter cough medicine has not been found to be effective, nor has the use of zinc supplementation in children. There is insufficient evidence for mucolytics. There is no strong evidence to recommend that children who have non-measles related pneumonia take vitamin A supplements. Vitamin D, as of 2023, is of unclear benefit in children. Vitamin C administration in pneumonia needs further research, although it can be given to patient of low plasma vitamin C because it is not expensive and low risk.

Pneumonia can cause severe illness in a number of ways, and pneumonia with evidence of organ dysfunction may require intensive care unit admission for observation and specific treatment. The main impact is on the respiratory and the circulatory system. Respiratory failure not responding to normal oxygen therapy may require heated humidified high-flow therapy delivered through nasal cannulae, non-invasive ventilation, or in severe cases mechanical ventilation through an endotracheal tube. Regarding circulatory problems as part of sepsis, evidence of poor blood flow or low blood pressure is initially treated with 30 mL/kg of crystalloid infused intravenously. In situations where fluids alone are ineffective, vasopressor medication may be required.

For adults with moderate or severe acute respiratory distress syndrome (ARDS) undergoing mechanical ventilation, there is a reduction in mortality when people lie on their front for at least 12 hours a day. However, this increases the risk of endotracheal tube obstruction and pressure sores.

Bacterial

Antibiotics improve outcomes in those with bacterial pneumonia. The first dose of antibiotics should be given as soon as possible. Increased use of antibiotics, however, may lead to the development of antimicrobial resistant strains of bacteria. Antibiotic choice depends initially on the characteristics of the person affected, such as age, underlying health, and the location the infection was acquired. Antibiotic use is also associated with side effects such as nausea, diarrhea, dizziness, taste distortion, or headaches. In the UK, treatment before culture results with amoxicillin is recommended as the first line for community-acquired pneumonia, with doxycycline or clarithromycin as alternatives. In North America, amoxicillin, doxycycline, and in some areas a macrolide (such as azithromycin or erythromycin) is the first-line outpatient treatment in adults. In children with mild or moderate symptoms, amoxicillin taken by mouth is the first line. The use of fluoroquinolones in uncomplicated cases is discouraged due to concerns about side-effects and generating resistance in light of there being no greater benefit.

For those who require hospitalization and caught their pneumonia in the community the use of a β-lactam such as cephazolin plus a macrolide such as azithromycin is recommended. A fluoroquinolone may replace azithromycin but is less preferred. Antibiotics by mouth and by injection appear to be similarly effective in children with severe pneumonia.

The duration of treatment has traditionally been seven to ten days, but increasing evidence suggests that shorter courses (3–5 days) may be effective for certain types of pneumonia and may reduce the risk of antibiotic resistance. Research in children showed that a shorter, 3-day course of amoxicillin was as effective as a longer, 7-day course for treating pneumonia in this population. For pneumonia that is associated with a ventilator caused by non-fermenting Gram-negative bacilli (NF-GNB), a shorter course of antibiotics increases the risk that the pneumonia will return. Recommendations for hospital-acquired pneumonia include third- and fourth-generation cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and vancomycin. These antibiotics are often given intravenously and used in combination. In those treated in hospital, more than 90% improve with the initial antibiotics. For people with ventilator-acquired pneumonia, the choice of antibiotic therapy will depend on the person's risk of being infected with a strain of bacteria that is multi-drug resistant. Once clinically stable, intravenous antibiotics should be switched to oral antibiotics. For those with Methicillin resistant Staphylococcus aureus (MRSA) or Legionella infections, prolonged antibiotics may be beneficial.

The addition of corticosteroids to standard antibiotic treatment appears to improve outcomes, reducing death and morbidity for adults with severe community acquired pneumonia, and reducing death for adults and children with non-severe community acquired pneumonia. A 2017 review therefore recommended them in adults with severe community acquired pneumonia. A 2019 guideline however recommended against their general use, unless refractory shock was present. Side effects associated with the use of corticosteroids include high blood sugar. There is some evidence that adding corticosteroids to the standard PCP pneumonia treatment may be beneficial for people who are infected with HIV.

The use of granulocyte colony stimulating factor (G-CSF) along with antibiotics does not appear to reduce mortality and routine use for treating pneumonia is not supported by evidence.

Viral

Neuraminidase inhibitors may be used to treat viral pneumonia caused by influenza viruses (influenza A and influenza B). No specific antiviral medications are recommended for other types of community acquired viral pneumonias including SARS coronavirus, adenovirus, hantavirus, and parainfluenza virus. Influenza A may be treated with rimantadine or amantadine, while influenza A or B may be treated with oseltamivir, zanamivir or peramivir. These are of most benefit if they are started within 48 hours of the onset of symptoms. Many strains of H5N1 influenza A, also known as avian influenza or "bird flu", have shown resistance to rimantadine and amantadine. The use of antibiotics in viral pneumonia is recommended by some experts, as it is impossible to rule out a complicating bacterial infection. The British Thoracic Society recommends that antibiotics be withheld in those with mild disease. The use of corticosteroids is controversial.

Aspiration

In general, aspiration pneumonitis is treated conservatively with antibiotics indicated only for aspiration pneumonia. The choice of antibiotic will depend on several factors, including the suspected causative organism and whether pneumonia was acquired in the community or developed in a hospital setting. Common options include clindamycin, a combination of a beta-lactam antibiotic and metronidazole, or an aminoglycoside. Corticosteroids are sometimes used in aspiration pneumonia, but there is limited evidence to support their effectiveness.

Follow-up

The British Thoracic Society recommends that a follow-up chest radiograph be taken in people with persistent symptoms, smokers, and people older than 50. American guidelines vary, from generally recommending a follow-up chest radiograph to not mentioning any follow-up.

Prognosis

With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. It often takes a few weeks before most symptoms resolve. X-ray findings typically clear within four weeks and mortality is low (less than 1%). In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%. Pneumonia is the most common hospital-acquired infection that causes death. Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis. If pneumonia deteriorates after 72 hours, it could be due to nosocomial infection or excerbation of other underlying comorbidities. About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurological disorders, or due to new onset of pneumonia.

Complications may occur in particular in the elderly and those with underlying health problems. This may include, among others: empyema, lung abscess, bronchiolitis obliterans, acute respiratory distress syndrome, sepsis, and worsening of underlying health problems.

Clinical prediction rules

Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia. These rules are often used to decide whether to hospitalize the person.

Pleural effusion, empyema, and abscess

An X-ray showing a chest lying horizontally. The lower black area, which is the right lung, is smaller with a whiter area below it of a pulmonary effusion. Red arrows indicate size.
A pleural effusion: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung.

In pneumonia, a collection of fluid may form in the space that surrounds the lung. Occasionally, microorganisms will infect this fluid, causing an empyema. To distinguish an empyema from the more common simple parapneumonic effusion, the fluid may be collected with a needle (thoracentesis), and examined. If this shows evidence of empyema, complete drainage of the fluid is necessary, often requiring a drainage catheter. In severe cases of empyema, surgery may be needed. If the infected fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity. If the fluid is sterile, it must be drained only if it is causing symptoms or remains unresolved.

In rare circumstances, bacteria in the lung will form a pocket of infected fluid called a lung abscess. Lung abscesses can usually be seen with a chest X-ray but frequently require a chest CT scan to confirm the diagnosis. Abscesses typically occur in aspiration pneumonia, and often contain several types of bacteria. Long-term antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a surgeon or radiologist.

Respiratory and circulatory failure

Pneumonia can cause respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response. The lungs quickly fill with fluid and become stiff. This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, may require long periods of mechanical ventilation for survival. Other causes of circulatory failure are hypoxemia, inflammation, and increased coagulability.

Sepsis is a potential complication of pneumonia but usually occurs in people with poor immunity or hyposplenism. The organisms most commonly involved are Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae. Other causes of the symptoms should be considered such as a myocardial infarction or a pulmonary embolism.

Epidemiology

Main article: Epidemiology of pneumonia
Deaths from lower respiratory infections per million persons in 2012   24–120  121–151  152–200  201–241  242–345  346–436  437–673  674–864  865–1,209  1,210–2,085
Disability-adjusted life year for lower respiratory infections per 100,000 inhabitants in 2004   no data   less than 100   100–700   700–1,400   1,400–2,100   2,100–2,800   2,800–3,500   3,500–4,200   4,200–4,900   4,900–5,600   5,600–6,300   6,300–7,000   more than 7,000

Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world. It is a major cause of death among all age groups resulting in 4 million deaths (7% of the world's total death) yearly. Rates are greatest in children less than five, and adults older than 75 years. It occurs about five times more frequently in the developing world than in the developed world. Viral pneumonia accounts for about 200 million cases. In the United States, as of 2009, pneumonia is the 8th leading cause of death.

Children

In 2008, pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world). In 2010, it resulted in 1.3 million deaths, or 18% of all deaths in those under five years, of which 95% occurred in the developing world. Countries with the greatest burden of disease include India (43 million), China (21 million) and Pakistan (10 million). It is the leading cause of death among children in low income countries. Many of these deaths occur in the newborn period. The World Health Organization estimates that one in three newborn infant deaths is due to pneumonia. Approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available. The IDSA has recommended that children and infants with symptoms of CAP should be hospitalized so they have access to pediatric nursing care. In 2011, pneumonia was the most common reason for admission to the hospital after an emergency department visit in the U.S. for infants and children.

History

A poster with a shark in the middle of it, which reads "Pneumonia Strikes Like a Man-Eating Shark Led by its Pilot Fish the Common Cold"
WPA poster, 1936/1937

Pneumonia has been a common disease throughout human history. The word is from Greek πνεύμων (pneúmōn) meaning "lung". The symptoms were described by Hippocrates (c. 460–370 BC): "Peripneumonia, and pleuritic affections, are to be thus observed: If the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... When pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand." However, Hippocrates referred to pneumonia as a disease "named by the ancients". He also reported the results of surgical drainage of empyemas. Maimonides (1135–1204 AD) observed: "The basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking pleuritic pain in the side, short rapid breaths, serrated pulse and cough." This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the Middle Ages into the 19th century.

Edwin Klebs was the first to observe bacteria in the airways of persons having died of pneumonia in 1875. Initial work identifying the two common bacterial causes, Streptococcus pneumoniae and Klebsiella pneumoniae, was performed by Carl Friedländer and Albert Fraenkel in 1882 and 1884, respectively. Friedländer's initial work introduced the Gram stain, a fundamental laboratory test still used today to identify and categorize bacteria. Christian Gram's paper describing the procedure in 1884 helped to differentiate the two bacteria, and showed that pneumonia could be caused by more than one microorganism. In 1887, Jaccond demonstrated pneumonia may be caused by opportunistic bacteria always present in the lung.

Sir William Osler, known as "the father of modern medicine", appreciated the death and disability caused by pneumonia, describing it as the "captain of the men of death" in 1918, as it had overtaken tuberculosis as one of the leading causes of death at the time. This phrase was originally coined by John Bunyan in reference to "consumption" (tuberculosis). Osler also described pneumonia as "the old man's friend" as death was often quick and painless when there were much slower and more painful ways to die.

Viral pneumonia was first described by Hobart Reimann in 1938. Reimann, Chairman of the Department of Medicine at Jefferson Medical College, had established the practice of routinely typing the pneumococcal organism in cases where pneumonia presented. Out of this work, the distinction between viral and bacterial strains was noticed.

Several developments in the 1900s improved the outcome for those with pneumonia. With the advent of penicillin and other antibiotics, modern surgical techniques, and intensive care in the 20th century, mortality from pneumonia, which had approached 30%, dropped precipitously in the developed world. Vaccination of infants against Haemophilus influenzae type B began in 1988 and led to a dramatic decline in cases shortly thereafter. Vaccination against Streptococcus pneumoniae in adults began in 1977, and in children in 2000, resulting in a similar decline.

Society and culture

See also: List of notable pneumonia cases

Awareness

Due to the relatively low awareness of the disease, 12 November was declared in 2009 as the annual World Pneumonia Day, a day for concerned citizens and policy makers to take action against the disease.

Costs

The global economic cost of community-acquired pneumonia has been estimated at $17 billion annually. Other estimates are considerably higher. In 2012 the estimated aggregate costs of treating pneumonia in the United States were $20 billion; the median cost of a single pneumonia-related hospitalization is over $15,000. According to data released by the Centers for Medicare and Medicaid Services, average 2012 hospital charges for inpatient treatment of uncomplicated pneumonia in the U.S. were $24,549 and ranged as high as $124,000. The average cost of an emergency room consult for pneumonia was $943 and the average cost for medication was $66. Aggregate annual costs of treating pneumonia in Europe have been estimated at €10 billion.

References

Footnotes

  1. The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or certain medications), but this inflammation is more accurately referred to as pneumonitis.

Citations

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  3. ^ McLuckie A, ed. (2009). Respiratory disease and its management. New York: Springer. p. 51. ISBN 978-1-84882-094-4.
  4. ^ Pommerville JC (2010). Alcamo's Fundamentals of Microbiology (9th ed.). Sudbury, MA: Jones & Bartlett. p. 323. ISBN 978-0-7637-6258-2.
  5. ^ "Pneumonia – Causes and Risk Factors | NHLBI, NIH". nhlbi.nih.gov. 24 March 2022. Retrieved 1 October 2022.
  6. Caldeira D, Alarcão J, Vaz-Carneiro A, Costa J (July 2012). "Risk of pneumonia associated with use of angiotensin converting enzyme inhibitors and angiotensin receptor blockers: systematic review and meta-analysis". BMJ. 345 (jul11 1): e4260. doi:10.1136/bmj.e4260. PMC 3394697. PMID 22786934. Susceptibility is higher among elderly people (≥65 years)
  7. ^ "Complications and Treatments of Sickle Cell Disease | CDC". Centers for Disease Control and Prevention. 12 June 2019. Retrieved 6 May 2020.
  8. ^ "How Is Pneumonia Diagnosed?". NHLBI. 1 March 2011. Archived from the original on 7 March 2016. Retrieved 3 March 2016.
  9. ^ Hoare Z, Lim WS (May 2006). "Pneumonia: update on diagnosis and management". BMJ. 332 (7549): 1077–79. doi:10.1136/bmj.332.7549.1077. PMC 1458569. PMID 16675815.
  10. ^ "How Can Pneumonia Be Prevented?". NHLBI. 1 March 2011. Archived from the original on 7 March 2016. Retrieved 3 March 2016.
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  14. Leach RE (2009). Acute and Critical Care Medicine at a Glance (2nd ed.). Wiley-Blackwell. ISBN 978-1-4051-6139-8.
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Bibliography

External links

ClassificationD
External resources
Pneumonia
Infectious pneumonias
Pneumonias caused by
infectious or noninfectious agents
Noninfectious pneumonia
Diseases of the respiratory system
Upper RT
(including URTIs,
common cold)
Head
sinuses
Sinusitis
nose
Rhinitis
Vasomotor rhinitis
Atrophic rhinitis
Hay fever
Nasal polyp
Rhinorrhea
nasal septum
Nasal septum deviation
Nasal septum perforation
Nasal septal hematoma
tonsil
Tonsillitis
Adenoid hypertrophy
Peritonsillar abscess
Neck
pharynx
Pharyngitis
Strep throat
Laryngopharyngeal reflux (LPR)
Retropharyngeal abscess
larynx
Croup
Laryngomalacia
Laryngeal cyst
Laryngitis
Laryngopharyngeal reflux (LPR)
Laryngospasm
vocal cords
Laryngopharyngeal reflux (LPR)
Vocal fold nodule
Vocal fold paresis
Vocal cord dysfunction
epiglottis
Epiglottitis
trachea
Tracheitis
Laryngotracheal stenosis
Lower RT/
lung disease
(including LRTIs)
Bronchial/
obstructive
acute
Acute bronchitis
chronic
COPD
Chronic bronchitis
Acute exacerbation of COPD)
Asthma (Status asthmaticus
AERD
Exercise-induced
Bronchiectasis
Cystic fibrosis
unspecified
Bronchitis
Bronchiolitis
Bronchiolitis obliterans
Diffuse panbronchiolitis
Interstitial/
restrictive
(fibrosis)
External agents/
occupational
lung disease
Pneumoconiosis
Aluminosis
Asbestosis
Baritosis
Bauxite fibrosis
Berylliosis
Caplan's syndrome
Chalicosis
Coalworker's pneumoconiosis
Siderosis
Silicosis
Talcosis
Byssinosis
Hypersensitivity pneumonitis
Bagassosis
Bird fancier's lung
Farmer's lung
Lycoperdonosis
Other
Obstructive /
Restrictive
Pneumonia/
pneumonitis
By pathogen
By vector/route
By distribution
IIP
Other
Pleural cavity/
mediastinum
Pleural disease
Pleural effusion
Hemothorax
Hydrothorax
Chylothorax
Empyema/pyothorax
Malignant
Fibrothorax
Mediastinal disease
Other/general
Categories: