Legionella pneumophila is a bacteria that causes Legionnaires’ disease, a form of severe pneumonia which was first identified in 1976 during an American Legion convention in Philadelphia, Pennsylvania. The genus of Legionella contains more than 50 species, of which at least 24 have been associated with human infections. The best-characterized member of the genus, L. pneumophila, is the major causative agent of Legionnaires' disease, and comprises approximately 80 percent of reported human Legionella infections. L. pneumophila is a gram-negative, obligate aerobic bacteria that replicates within alveolar macrophages and epithelial cells. Each year, 8,000–18,000 people in the United States are hospitalized with Legionnaires’ disease. Smokers, the elderly, and individuals that are immunocompromised or have preexisting chronic lung disease are at higher risk of serious L. pneumophila infections that often are life-threatening.
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