[A minor epidemic due to Legionella pneumophila serogroup 1].

Ten days after starting military service in a police barracks a 25-year-old man developed left middle and lower lobe pneumonia which did not respond to ampicillin (8 g daily) and gentamycin (120 mg daily). Parenteral administration of doxycycline (100 mg daily) was equally ineffective. However, the fever fell on administration of cefotiam (4 g daily). Antibody tests demonstrated Legionella pneumophila serogroup 1 as the causative organism. Because of the confined accommodation of the conscripts the source of the infection was thought to be the hot water system in the barracks. In two other policemen the demonstration of antibodies and of urine antigens confirmed Legionella infection as cause of an acute respiratory illness (Pontiac disease). Legionella pneumophila serogroup 1 subtype Philadelphia, 1-8 colony-forming units per ml, was isolated from six of 14 hot water samples in the barracks. This subtype possesses a virulence-associated antigen which is found in the majority of patient isolates of Legionella pneumophila serogroup 1.