Legionnaires’ disease is a severe form of pneumonia — lung inflammation usually caused by infection. Legionnaires’ disease is caused by a bacterium known as legionella.
You can’t catch Legionnaires’ disease from person-to-person contact. Instead, most people get Legionnaires’ disease from inhaling the bacteria. Older adults, smokers and people with weakened immune systems are particularly susceptible to Legionnaires’ disease.
The legionella bacterium also causes Pontiac fever, a milder illness resembling the flu. Separately or together, the two illnesses are sometimes called legionellosis. Pontiac fever usually clears on its own, but untreated Legionnaires’ disease can be fatal. Although prompt treatment with antibiotics usually cures Legionnaires’ disease, some people continue to experience problems after treatment.
How is Legionnaires’ disease diagnosed?
Specialized laboratory tests are necessary and, unfortunately, may not be available in many hospitals. These include culture on specialized Legionella media. Culture media furnish nutrients for the bacterium. When sputum from the patients is placed onto the culture media, the bacterium grows on the medium and can be identified.
Other tests include direct fluorescent antibody (DFA) in which the bacterium can be stained and becomes visible under a fluorescent microscope. Antibody testing is a blood test in which antibodies that are reactive against Legionella are present in the human body showing that the patient has come into contact with the bacterium previously. Urinary antigen is a test that detects Legionella in the urine.