Legionella infections.

Legionnaires' disease is a distinct clinical entity caused by Legionella pneumophila. Following an epidemic of pneumonia in Philadelphia in 1976, it was found that the bacterium had in fact been first isolated in 1947. Other species of Legionella have been identified, many of which are indistinguishable from L. pneumophila infection. Legionella species also cause extrapulmonary infections and a mild nonpneumonic form of disease known in its epidemic form as Pontiac Fever.