A Sustained Outbreak of Clostridium difficile in a General Hospital: Persistence of a Toxigenic Clone in Four Units

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Abstract
Objective: To evaluate the endemicity and epidemiology of toxigenic Clostridium diflicile in a sustained outbreak of antibiotic-associated diarrhea. Setting: University-affiliated, 465-bed tertiary care teaching hospital with adjacent cancer clinic in Hamilton, Ontario. Design: From August 8, 1991, through August 31, 1993, a total of 187 cases were investigated for epidemiologic analysis oftoxigenic C difflcile from stool cultures, to identify the endemic clone(s). To assess the nature of contamination, cultures of inanimate surfaces in the patient environment from the four most affected units (medical teaching, nonteaching medical, hematologic oncology, and the intensive care unit) were processed for C difficile. The 229 clinical strains and 24 environmental strains isolated were typed bynumerical analysis of SDS-PAGE protein patterns. Results: A majority (81%) of cases in the epidemiologic analysis were associated with a toxigenic electrophoretic (EP) type 1 C ditfficile that was identical to the strain first isolated from an index case that occurred 18 months before the start of this study. Culture and typing of the C difflicile strains from the inanimate surfaces in the four most affected units showed that the patient environment was contaminated with the toxigenic EP type 1 organism. Six other strains that occurred infrequently among cases also were found in the environment. Conclusions: A single predominant toxigenic clone has been implicated in a sustained outbreak of antibiotic-associated diarrhea that affected elderly patients. The "endemic" clone transmitted for the 25-month study period was linked to an index case shedding a toxigenic EP type 1 strain that occurred 21 months prior to the intial outbreak on the medical teaching unit. The patient environment in the affected units was found to be contaminated with the same clone, possibly due to shedding of organisms by fecally incontinent symptomatic patients. The extrinsic factors contributing to the endemic transmission of this one clone still are not well understood.