Surveillance for Methicillin Resistant Staphylococcus aureus (MRSA) in Canadian Hospitals.

A.E. SIMOR*, S. PATON, M. OFNER, W. JOHNSON, J. SMITH,

The Canadian Hospital Epidemiology committee and the Canadian Nosocomial Infection Surveillance Program, Health Canada

In an effort to characterize the epidemiology of MRSA in Canada, a collaborative study was conducted during 1995 involving 20 sentinel hospitals from across the country. For each in-patient from whom MRSA was identified, a standardized questionnaire providing detailed epidemiologic information was completed. All isolates were submitted to central laboratory for micro dilution broth susceptibility testing, mecA gene probing and pulsed-field gel electrophoresis(PFGE). A total of 117 cases of MRSA were identified in 12 hospitals, ranging from 2-26 cases/site, and with a mean of 7.3 MRSA per 1,000 S. Aureus isolates. Eight hospitals did not identify any MRSA in 1995. Six cases were identified in children<15 yrs, including 4 infants less than 1 year of age. Eighteen cases were identified in aboriginal people. The occurrence of MRSA varied across the country: 54% of cases were from western Canada, 39% from central Canada and 7% from eastern Canada. Of 81 cases where the site of MRSA acquisition was known, 20% were community-acquired, 75% were acquired in acute-care facilities and 5% were acquired in long-term care facilities. Forty-seven (40%) patients were colonized with MRSA without infection; 70(60%) had a least one infected site. An epidemiological link with a previously identified MRSA patient was suspected in 32% of cases. Molecular typing by PFGE demonstrated considerable genetic diversity of MRSA across the country, although common strains were identified within several institutions. This study is the first national attempt to characterize MRSA in Canadian hospitals. Preliminary results demonstrate that MRSA is occurring in the majority of participating sites, although MRSA represents less than 2% of S. Aureus isolated at each hospital. In many of the centres, there is epidemiologic and molecular evidence of cross-infection. Further studies of MRSA in the sentinel hospitals are ongoing.