[Microbiological aspects of Legionnaires' disease].

Legionella pneumophila was isolated in 1947 but its etiological role was only recognized after the Philadelphia outbreak in 1976. Since then, infections with Legionella pneumophila in patients with so-called atypical pneumonia have been found in different parts of the world in sporadic cases and outbreaks affecting up to several hundred patients. The etiological agent is a bacterium which can be found in dust, mud and water. Transmission to the human most likely occurs through water-cooled air condition units or showers. Air conditioning in hotels, hospitals and offices may transmit the organism and lead to infection which, moreover, is more frequent during the warm season. The diagnosis is based on clinical data and the demonstration of specific antibodies. Isolation of the agent is technically difficult and up to now only approximately 3% of the cases have been confirmed by isolation of the agent. Evidence of Legionella pneumophila infection in Switzerland was obtained by testing stored blood samples from transplanted patients in 1970. Sporadic cases were observed in the period 1977 to 1980. Acute infection was considered in 141 patients on the basis of serological results. Approximately 3% of all pneumonias in 1979 were caused by Legionella pneumophila. Isolation of the etiological agent has been achieved in 3 patients only.