[Legionnaires' disease: Legionella pneumophila, an agent in nosocomial infection].

Legionella pneumophila recently identified in 1977 as responsible for legionnaires' disease, is present in the natural environment. The discovery of the bacteria, the development of suitable complex media ( BCYE ) and of serological techniques improved the knowledge of epidemiologic features of L. pneumophila widely distributed geographically. Legionella has been frequently isolated from the aquatic environment: the organism is able to colonize the condensed water of air-conditioning systems and the water-supply system in public buildings. The presence of Legionella in hospitals constitutes a danger for immunosuppressed patients.