Persistence of Legionella pneumophila in a hospital's water system: a 13-year survey.

OBJECTIVE: To describe the molecular epidemiology of Legionella pneumophila infections in the University of Iowa Hospitals and Clinics (UIHC). DESIGN: Molecular epidemiological study using pulsed-field gel electrophoresis (PFGE). SETTING: A large university teaching hospital. ISOLATES: All surviving isolates obtained from culture-proven nosocomial L. pneumophila infections and all surviving isolates obtained from the University of Iowa Hospital and Clinics' water supply between 1981 and 1993. RESULTS: Thirty-three isolates from culture-proven nosocomial cases of L. pneumophila pneumonia were available for typing. PFGE of genomic DNA from the clinical isolates identified six different strains. However, only strain C (16 cases) and strain D (13 cases) caused more than 1 case. Strain C caused clusters of nosocomial infection in 1981, 1986, and 1993 and also caused 4 sporadic cases. Strain D caused a cluster in 1987 and 1988 plus 4 sporadic cases. Of the six strains causing clinical infections, only strains C and D were identified in water samples. PFGE identified three strains in the water supply, of which strains C and D caused clinical disease and also persisted in the water supply during most of the study period. CONCLUSION: Specific strains of L. pneumophila can colonize hospital water supplies and cause nosocomial infections over long periods of time.