Nosocomial pneumonia caused by three genetically different strains of Legionella pneumophila and detection of these strains in the hospital water supply.

A 44-year-old woman developed Legionella pneumophila pneumonia after cerebral surgery. Initially, one colony from a clinical specimen and two colonies from water samples, all belonging to serogroup 12, did not match when their DNA restriction patterns were compared. When additional colonies from the water specimens were analyzed, a serogroup 12 strain complementary to that found in the clinical specimen was identified. Other colonies from the clinical specimen were identified as serogroup 12 strains complementary to those identified from the water. In addition, the same serogroup 1 strain was isolated from the patient and the water system.