Health care-associated Clostridium difficile infection in Canada: patient age and infecting strain type are highly predictive of severe outcome and mortality.

BACKGROUND C. difficile infection (CDI) has become an important and frequent nosocomial infection, often resulting in severe morbidity or death. Severe CDI is more frequently seen among individuals infected with the emerging NAP1/027/BI (NAP1) strain and in the elderly population, but the relative importance of these 2 factors remains unclear. We used a large Canadian database of patients with CDI to explore the interaction between these 2 variables. METHODS The Canada-wide CDI study, performed in 2005 by the Canadian Nosocomial Infection Surveillance Program (CNISP), was used to analyze the role of infecting strain type and patient age on the severity of CDI. A severe outcome was defined as CDI requiring intensive care unit care, colectomy, or causing death (directly or indirectly) within 30 days after diagnosis. RESULTS A total of 1008 patients in the CNISP database had both complete clinical data and infecting strain analysis documented. A total of 311 patients (31%) were infected with the NAP1 strain, 83 (28%) were infected with the NAP2/J strain, and the rest were infected with various other types. The proportion of NAP1 infections correlated with the incidence and the severity of CDI when analyzed by province. Thirty-nine (12.5%) of the infections due to the NAP1 strain resulted in a severe outcome, compared with only 41 (5.9%) of infections due to the other types (P < .001). The patient's age was strongly associated with a severe outcome, and patients 60-90 years of age were approximately twice as likely to experience a severe outcome if the infection was due to NAP1, compared with infections due to other types. CONCLUSIONS Our study confirms the strong age association with infection due to the NAP1 strain and severe CDI. In addition, patients 60-90 years of age infected with NAP1 are approximately twice as likely to die or to experience a severe CDI-related outcome, compared with those with non-NAP1 infections. Patients >90 years of age experience high rates of severe CDI, regardless of strain type.