Background: Clostridium difficile infection (CDI) is related to the use of antibiotics and ranges in severity from mild diarrhea to pseudomembranous colitis and death. A new strain of C. difficile (polymerase chain reaction ribotype 027) has been associated with increased severity of CDI and outbreaks but is still uncommon in New Zealand or Australia. The mortality related to CDI in the Canterbury District Health Board region is unknown.Methods: This was a case-control study. Cases (167) were all patients testing positive for C. difficile toxins A and B during 2009/2010 in the DHB's hospitals. Two control subjects (334) testing negative were selected from the same database as the cases and matched for age, sex, and admission to the same medical specialty. Potential predictors of complications such as mortality before 30 days were assessed.Results: The median age was 73 years (range, 1Y99 years). Overall 30-day mortality was 17% for the cases and 9% for the control subjects (P G 0.01). Males had an increased mortality (P G 0.01). Mortality was increased in untreated cases (P G 0.01) and cases with white blood cell (WBC) count outside the reference range (P G 0.01).Conclusions: Even in hospitals with a low CDI rate, there might be significant mortality in the older age group, with an increased risk of mortality in males and patients not treated for CDI.