There was an increase in the Clostridium difficile infection (CDI) rate in our bone marrow transplantation unit. To evaluate the role of unit-based transmission, C. difficile screening was performed on adult patients admitted for hematopoietic stem cell transplantation (HSCT) over a 2-year period, and C. difficile isolates were typed. C. difficile testing was performed using a 2-step C. difficile glutamate dehydrogenase antigen plus toxin A/B enzyme immunoassay (EIA) and cytotoxin assay (or molecular toxin assay). Multilocus sequence typing (MLST) was performed on toxin-positive whole stool samples. A retrospective chart review was performed on all patients with a positive toxin assay. Sixteen of 150 patients (10.7%) had toxigenic C. difficile colonization (CDC) on admission. The overall incidence of CDI within 100 days after HSCT was 24.7% (37 of 150). The median time to diagnosis of CDI was 3.5 days after HSCT. In an adjusted logistic regression model, CDC on admission was a significant risk factor for CDI (odds ratio, 68.5; 95% confidence interval, 11.4 to 416.2). MLST on 22 unit patient toxin-positive stool specimens revealed 15 distinct strain types. Further analysis identified at least 1 potential cross-transmission event; some events may have been missed because of incomplete typing from other specimens. Despite aggressive infection control interventions, there was no decline in the number of CDI cases during the study period. These data suggest that prior CDC plays a major role in CDI rates in this high-risk patient population. It remains unclear if CDI was cross-transmitted in the unit.

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