Community-associated methicillin-resistant Staphylococcus aureus in northwest Ontario: A five-year report of incidence and antibiotic resistance.

Background: The incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is traditionally high in remote areas of Canada with large Aboriginal populations. Northwestern Ontario is home to 28,000 First Nations people in more than 30 remote communities; rates of CA-MRSA are unknown.

Objective: To determine the CA-MRSA rates and antibiotic susceptibilities in this region.

Methods: A five-year review of laboratory and patient CA-MRSA data and antibiotic susceptibility was undertaken.

Results: In 2012, 56% of S aureus isolates were CA-MRSA strains, an increase from 31% in 2008 (P=0.06). Reinfection rates have been increasing faster than new cases and, currrently, 25% of infections are reinfections. CA-MRSA isolates continue to be susceptible to many common antibiotics (nearly 100%), particularly trimethoprim/sulfamethoxazole, clindamycin and tetracycline. Erythromycin susceptibility stands at 58%.

Discussion: Rates of CA-MRSA, as a percentage of all S aureus isolates, were higher than those reported in other primary care series. The infection rate per 100,000 is one the highest reported in Canada. Antibiotic susceptibilities were unchanged during the study period; the 99% susceptibility rate to clindamycin differs from a 2010 Vancouver (British Columbia) study that reported only a 79% susceptibility to this antibiotic.

Conclusion: There are very high rates of CA-MRSA infections in northwestern Ontario. Disease surveillance and ongoing attention to antibiotic resistance is important in understanding the changing profile of MRSA infections. Social determinants of health, specifically improved housing and sanitation, remain important regional issues.