Molecular heterogeneity of Acinetobacter baumanii isolates during seasonal increase in prevalence.

OBJECTIVE: To study the epidemiology of Acinetobacter baumanii during a period of increased seasonal prevalence. DESIGN: Descriptive molecular and clinical epidemiologic study of A baumanii isolates from 1990 through 1992. SETTING: A 770-bed urban, acute, tertiary-care university hospital. RESULTS: During 1990 through 1992, the rate of A baumanii isolations was 30.4 per 1,000 culture isolations during the summer, compared to 12.6 per 1,000 culture isolations during the fall, winter, and spring (P < .000001). There were 320 isolates identified among 260 patients during this time. Eighty-one patients with isolates available were identified for evaluation; they ranged in age from 2 months to 95 years. Pulsed-field gel electrophoresis (PFGE) typing showed that 59 (83%) of 71 typed isolates had distinct PFGE patterns. There were three small clusters of isolates with the same PFGE patterns, suggesting cross-transmission in those instances. CONCLUSIONS: A seasonally increased prevalence of A baumanii largely associated with device-related nosocomial infections in severely ill patients was noted over a 3-year period. Although there were isolated instances of cross-transmission, most isolates had distinct PFGE patterns. Clonal dissemination of a single strain was not responsible for the seasonal increased prevalence of A baumanii. PFGE typing was useful in directing control efforts.