Predominance of a Single Restriction Endonuclease Analysis Group with Intrahospital Subgroup Diversity AmongClostridium difficileIsolates at Two Chicago Hospitals

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Abstract
Objective: To determine the epidemiology and relatedness ofClostridium difficileisolates in two geographically separated hospitals in a large metropolitan area, each with unique patients and personnel.Design: Observational descriptive molecular epidemiology of clinicalC. difficileisolates.Setting: Two tertiary-care hospitals in Chicago.Methods: ConsecutiveC. difficileisolates from the clinical laboratory of a Veterans Affairs hospital during a 13-month period were typed by restriction endonuclease analysis (REA). During an overlapping 3-month period, stool specimens that tested positive forC. difficiletoxin from patients at a nearby county hospital were cultured and the recovered isolates typed by the same method.Results: Nineteen (68%) of 28 nosocomial isolates at the smaller, Veterans Affairs hospital belonged to REA group K. Within this group of closely related strains, 9 distinct REA types were recognized. Twenty-one (72%) of 29 nosocomial isolates at the larger, county hospital also belonged to group K. However, the predominant REA types within group K differed markedly at each institution.Conclusions: These findings demonstrate a high degree of similarity among nosocomialC. difficilestrains from different hospitals in the same city and suggest the possibility of an extended outbreak of a prototype group K strain with subsequent genetic drift at the two different institutions.