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Community-acquired pneumonia (CAP) is a disease in which individuals who are otherwise healthy develop an infection of the lungs (pneumonia). CAP is a common illness and can affect people of all ages. CAP often causes problems breathing, fever, chest pains, and a cough. CAP occurs because the areas of the lung which absorb oxygen (alveoli) from the atmosphere become filled with fluid and cannot work effectively. CAP occurs throughout the world and is a leading cause of illness and death. There are many different causes of CAP, including bacteria, viruses, fungi, and parasites. CAP can be diagnosed by symptoms and physical examination alone, though x-rays, examination of the sputum, and other tests are often used. Individuals with CAP sometimes require treatment in a hospital. CAP is primarily treated with antibiotic medication. Some forms of CAP can be prevented by vaccination. Administrator note

Symptoms

Symptoms of CAP commonly include problems breathing; coughing that produces greenish or yellow sputum; a high fever that may be accompanied with sweating, chills, and uncontrollable shaking; sharp or stabbing chest pain; and rapid, shallow breathing that is often painful. Less commonly, there may be the coughing up of blood (hemoptysis), headaches (including migraine headaches), loss of appetite, excessive fatigue, blueness of the skin (cyanosis), nausea, vomiting, diarrhea, joint pain (arthalgia) or muscle aches (myalgia). The manifestations of pneumonia, like those for many conditions, may not be typical in older people. They may instead experience new or worsening confusion, hypothermia, or falls. Infants may be overly sleepy and have difficulties feeding.  Administrator note

Diagnosis

Individuals with symptoms of CAP require further evaluation. Physical examination by a health provider may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia), and/or changes in the amount of oxygen in the blood. Feeling the way the chest expands (palpation) and tapping the chest wall (percussion) to identify dull areas which do not resonate can identify areas of the lung which are stiff and full of fluid (consolidated). Examination of the lungs with the aid of a stethoscope can reveal several things. A lack of normal breath sounds or the presence of crackling sounds (rales) when the lungs are listened to (auscultated) can also indicate consolidation. Increased vibration of the chest when speaking (tactile fremitus) and increased volume of whispered speech during auscultation of the chest can also reveal consolidation.  Administrator note

X-rays of the chest, examination of the blood and sputum for infectious microorganisms, and blood tests are commonly used to diagnose individuals with suspected CAP based upon symptoms and physical examination. The use of each test depends on the severity of illness, local practices, and the concern for any complications resulting from the infection.

All patients with CAP should have the amount of oxygen in their blood monitored with a machine called a pulse oximetry. This helps determine how well the lungs are able to work despite infection. In some cases, analysis of arterial blood gas may be required to accurately determine the amount of oxygen in the blood. Chest x-rays and chest computed tomography (CT) can reveal areas of opacity (seen as white) which represent consolidation. A normal chest x-ray makes CAP less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray. In some cases, chest CT can reveal a CAP which is not present on chest x-ray. X-rays can often be misleading, as many other diseases can mimic CAP such as heart problems or other types of lung damage. Administrator note

Pathophysiology

The symptoms of CAP are the result of both the invasion of the lungs by microorganisms and the immune system's response to the infection. The mechanisms of infection are quite different for viruses and the other microorganisms.

• Viruses

Viruses must invade cells in order to reproduce. Typically, a virus will reach the lungs by traveling through the mouth and nose with inhalation. There, the virus invades the cells lining the airways and the alveoli. This invasion often leads cell death either through direct killing by the virus or by self-destruction through apoptosis. Further damage to the lungs occurs when the immune system responds to the infection. White blood cells, in particular lymphocytes, are responsible for activating a variety of chemicals (cytokines) which cause leaking of fluid into the alveoli. The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream, resulting in potentially serious illness.

• Bacteria and fungi

Bacteria and fungi also typically enter the lung with inhalation, though they can reach the lung through the bloodstream if other parts of the body are infected. Once inside the alveoli, bacteria and fungi travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system to respond by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs. The neutrophils engulf and kill the offending organisms but also release cytokines which result in a general activation of the immune system. This results in the fever, chills, and fatigue common in CAP. The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation.

• Parasites

There are a variety of parasites which can affect the lungs. In general, these parasites enter the body through the skin or by being swallowed. Once inside the body, these parasites travel to the lungs, most often through the blood. There, a similar combination of cellular destruction and immune response causes disruption of oxygen transportation.

Microbiology

Treatment and Prognosis

The treatment and prognosis of people with CAP depends in large part on characteristics such as age, underlying illnesses, type of microorganism causing infection, and the initial symptoms and degree of illness. In 2001, the American Thoracic Society, drawing on work by the British and Canadian Thoracic Societies, established guidelines for the management of adults with CAP which divided individuals with CAP into four categories.  Administrator note

Epidemiology

References

1. Template:Anb Emedicine review of bacterial pneumonia
2. Template:Anb Metaly JP, Schulz R, Li Y-H, Singer DE, Marrie TJ, Coley CM, Hough LJ, Obrosky DS, Kapoor WN, Fine MJ. Influence of age on symptoms at presentation in patients with community-acquired pneumonia. Arch Intern Med 1997; 157: 1453-1459 PMID 9224224
3. Template:Anb 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
4. Template:Anb Syrjala H, Broas M, Suramo I, Ojala A, Lahde S. High resolution computed tomography for the diagnosis of community-acquired pneumonia. Clin Infect Dis 1998; 27: 358-363 PMID 9709887
5. Template:AnbNiederman MS, Mandell LA, Anzueto A, Bass JB, Broughton WA, Campbell GD, Dean N, File T, Fine MJ, Gross PA, et al. Guidelines for the management of adults with community-acquired pneumonia: diagnosis, assessment of severity, antimicrobial therapy, and prevention. Am J Respir Crit Care Med 2001;163:1730–1754 PMID 11401897

See also

Pneumonia

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