legionnaire's disease

Syn: legionellosis. A form of bronchopneumonia caused by an elusive Gram-negative microorganism, Legionella pneumophila, that is transmitted person to person and by water vapor in humid environments. The name derives from epidemiological investigations of an epidemic among members of the American Legion who attended a convention in Philadelphia in 1976 and were infected by moist air from a hotel air conditioning plant that was a common vehicle for transmission of the pathogenic organism. A nonpneumonic form of the disease, called Pontiac fever, was identified before 1976.