Legionnaires' disease

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Legionellosis is an infection caused by the bacterium Legionella (legionella pneumophila and other legionella species). At least 46 species and 70 serogroups have been identified. L. pneumophila, an ubiquitous aquatic organism that thrives in warm environments (32°- 45°C) causes over 90% of Legionnaires Disease in the United States.

The disease has two distinct forms:

Legionnaires' disease is the name for the more severe form of infection which includes pneumonia, and
Pontiac fever is a milder respiratory illness without pneumonia caused by the same bacterium

Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among persons attending a convention of the American Legion in Philadelphia. Later, the bacterium causing the illness was named Legionella.

On January 18, 1977 scientists identified a previously unknown bacterium as the cause of the mysterious "Legionnaire's disease."

An estimated 8,000 to 18,000 people get Legionnaires' disease in the United States each year. Some people can be infected with the Legionella bacterium and have mild symptoms or no illness at all.

Outbreaks of Legionnaires' disease receive significant media attention. However, this disease usually occurs as a single, isolated case not associated with any recognized outbreak. When outbreaks do occur, they are usually recognized in the summer and early fall, but cases may occur year-round. About 5% to 30% of people who have Legionnaires' disease die.

What are the usual symptoms of legionellosis?

Patients with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Some patients also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory tests may show that these patients' kidneys are not functioning properly. Chest X-rays often show pneumonia. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone; other tests are required for diagnosis.

Persons with Pontiac fever experience fever and muscle aches and do not have pneumonia. They generally recover in 2 to 5 days without treatment.

The time between the patient's exposure to the bacterium and the onset of illness for Legionnaires' disease is 2 to 10 days; for Pontiac fever, it is shorter, generally a few hours to 2 days.

Legionella

The bacterium Legionella pneumophilia belongs to the gram negative class of bacteria (LEGIONELLACEAE). On the side-chains of the cell wall are carried the bases for the somatic antigen specifity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are such important means of serologically classifying many Gram-negative.

At least 14 different serovars of L. pneumophila have been described as well as several other species being subdivided into a number of serovars. Sera have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and microagglutination tests have also been successfully applied.

Legionella pneumophila is non-acid, fast non-capsulated rods, aerobic and do not hydrolyse gelatin or produce urease. They are non-fermentative. L. pneumophila is neither pigmented nor does it autofluoresce. It is oxidase and catalase positive, produces beta-lactamase.

L. pneumophila is an intracellar pathogen. The internalisation of the bacteria is enhanced by the presence of antibody and complement. A pseudopod coils around the bacterium in this unique form of phagocytosis. Once internalised, the bacteria surround themselves by a membrane-bound phagolysosome. This becomes a vescicle, within which the bacteria multiply. They produce a 39kDa metalloprotease into culture fluids, which is cytotoxic for some cultured tissue culture cells.

The legionellosis pathogen is Legionella pneumophila and other Legionella species (at least 46 species and 70 serogroups).

Infections

Intestinal Infections: These may only occur as part of respiratory infections, where gastrointestinal symptoms have on occasion been described.

Extraintestinal Infections: L. pneumophila is specifically considered as a pathogen of the respiratory tract, where it is a cause of atypical pneumonia, also known as Legionnaires' disease. Other infections have also been reported, including haemodialysis fistulae, pericarditis and wound and skin infections.Bacteraemia is often associated with Legionnaires' disease.

Animal Infections: None specifically recorded. Infections of Protozoa: Protozoa such as Harmanella vermiformis and related protozoa have been shown to be able to support the growth of L. pneumophila in tap water. Also Acanthamoeba , Naegleria and Tetrahymena can be infected by L. pneumophila . It is considered that this may be how these fastidious organisms survive in the environment.

How is legionellosis diagnosed?

The diagnosis of legionellosis requires special tests not routinely performed on persons with fever or pneumonia. Therefore, a physician must consider the possibility of legionellosis in order to obtain the right tests.

Several types of tests are available. The most useful tests detect the bacteria in sputum, find Legionella antigens in urine samples, or compare antibody levels to Legionella in two blood samples obtained 3 to 6 weeks apart.

Who gets legionellosis?

People of any age may get Legionnaires' diasease, but the illness most often affects middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Also at increased risk are persons whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those that take drugs that suppress the immune system are also at higher risk.

Pontiac fever most commonly occurs in persons who are otherwise healthy.

Treatment of legionellosis

Erythromycin is the antibiotic currently recommended for treating persons with Legionnaires' disease. In severe cases, a second drug, rifampin, may be used in addition. Other drugs are available for patients unable to tolerate erythromycin.

Pontiac fever requires no specific treatment.

How is legionellosis spread?

Outbreaks of legionellosis have occurred after persons have breathed mists that come from a water source (e.g., air conditioning cooling towers, whirlpool spas, showers) contaminated with Legionella bacteria. Persons may be exposed to these mists in homes, workplaces, hospitals, or public places. Legionellosis is not passed from person to person, and there is no evidence of persons becoming infected from auto air conditioners or household window air-conditioning units.

Where is the Legionella bacterium found?

Legionella organisms can be found in many types of water systems. However, the bacteria reproduce to high numbers in warm, stagnant water (90°-105° F, 32°-40° C), such as that found in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems, and whirlpool spas. Cases of legionellosis have been identified throughout the United States and in several foreign countries. It is believed to occur worldwide.

What is being done to prevent legionellosis?

Improved design and maintenance of cooling towers and plumbing systems to limit the growth and spread of Legionella organisms are the foundations of legionellosis prevention.

During outbreaks, CDC and health department investigators seek to identify the source of disease transmission and recommend appropriate prevention and control measures, such as decontamination of the water source. Current research will likely identify additional prevention strategies.

World´s more important outbreaks

In March, 1999 an outbreak in the Netherlands occurred during a flower exhibition in Bovenkarspel. 200 people became ill and at least 32 people died. Probably more people died, o.a. in the hospital of Hoorn and were buried before Legionella infection was recognized. The source of the bacteria were probably a whirlpool and a moisterizer in the exhibition area.

The world's largest outbreak of legionnaries'disease happened in July 2001 (the patients began to go to the hospital on July 7), in Murcia, Spain, where more than 800 suspected cases were reported; 636–696 of these cases were estimated and 449 confirmed (so, at least 16,000 persons was exposed to the bacterium) and 6 dead (this is, with a case-fatality rate of aprox. 1%.).

A case-control study matching 85 patients living outside the city of Murcia with two controls each was undertaken to identify the outbreak source; the epidemiologic investigation implicated the cooling towers at a city hospital (Morales Meseguer Hospital). An environmental isolate from these towers with an identical molecular pattern as the clinical isolates was subsequently identified and supported that epidemiologic conclusion.

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