OBJECTIVES: Given the traditionally low CDAD (Clostridium difficile associated diarrhoea) prevalence in Switzerland, CDAD patients are not routinely contact-isolated in our institution. In light of the globally changing C. difficile epidemiology, we sought to determine our institutional CDAD rate and to detect possible hospital transmission by means of epidemiological linkage. METHODS: We included every CDAD patient hospitalised in our institution, a tertiary-care hospital in eastern

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... , in 2009/2010. Patients with healthcare facility associated (HCFA) CDAD were grouped into cases with and without exposure to an infectious CDAD patient. Exposure was defined as sharing the room/ward with an infectious patient before symptom onset, either at the same time or within 30 days after discharge of the infectious patient. Molecular strain typing was not performed. RESULTS: We registered 141 CDAD episodes. Among them 108 were HCFA (associated with our institution), corresponding to an incidence of 2.3/10,000 patient days. Fifty-six percent (60/108) were exposed to an infectious CDAD patient, suggesting hospital transmission. The number of patients without exposure remained relatively stable, whereas presumably transmitted cases -often occurring within spatiotemporal clusters -showed high variability over time. Presumably transmitted cases were significantly older (p = 0.032) and more likely to have a Charlson score >1 (p = 0.001). Abbreviations CA community associated CO community onset CCNA cell culture cytotoxicity neutralisation assay CDAD Clostridium difficile associated diarrhoea HCFA healthcare facility associated HO healthcare onset HIV human immunodeficiency virus MLST multilocus sequence typing PCR polymerase chain reaction PFGE pulsed field gel electrophoresis PPI proton-pump inhibitor CONCLUSION: In our setting, 56% of healthcare associated CDAD cases have been exposed to an infectious CDAD patient. In view of the clustering of these presumed hospital transmissions, we consider an intensification of our current infection control measures, mainly on wards with elderly and comorbid patients which are particularly prone to C. difficile transmission.