The Evolving Epidemiology of Infection in Canadian Hospitals During a Postepidemic Period (2009-2015)

Background: The clinical and molecular epidemiology of health care-associated infection in nonepidemic settings across Canada has evolved since the first report of the virulent North American pulsed-field gel electrophoresis type 1 (NAP1) strain more than 15 years ago. The objective of this national, multicentre study was to describe the evolving epidemiology and molecular characteristics of health care-associated infection in Canada during a post-NAP1-epidemic period, particularly patient outcomes associated with the NAP1 strain.

Methods: Adult inpatients with infection were prospectively identified, using a standard definition, between 2009 and 2015 through the Canadian Nosocomial Infection Surveillance Program (CNISP), a network of 64 acute care hospitals. Patient demographic characteristics, severity of infection and outcomes were reviewed. Molecular testing was performed on isolates, and strain types were analyzed against outcomes and epidemiologic trends.

Results: Over a 7-year period, 20 623 adult patients admitted to hospital with health care-associated infection were reported to CNISP, and microbiological data were available for 2690 patients. From 2009 to 2015, the national rate of health care-associated infection decreased from 5.9 to 4.3 per 10 000 patient-days. NAP1 remained the dominant strain type, but infection with this strain has significantly decreased over time, followed by an increasing trend of infection with NAP4 and NAP11 strains. The NAP1 strain was significantly associated with a higher rate of death attributable to infection compared with non-NAP1 strains (odds ratio 1.91, 95% confidence interval [CI] 1.29-2.82). Isolates were universally susceptible to metronidazole; one was nonsusceptible to vancomycin. The proportion of NAP1 strains within individual centres predicted their rates of health care-associated infection; for every 10% increase in the proportion of NAP1 strains, the rate of health care-associated infection increased by 3.3% (95% CI 1.7%-4.9%).

Interpretation: Rates of health care-associated infection have decreased across Canada. In nonepidemic settings, NAP4 has emerged as a common strain type, but NAP1, although decreasing, continues to be the predominant circulating strain and remains significantly associated with higher attributable mortality.