Changing epidemiology of methicillin-resistant Staphylococcus aureus in Canada

To compare the demographics, antimicrobial susceptibilities and molecular epidemiology of community-associated (CA) and healthcare-associated (HA) methicillin-resistant Staphylococcus aureus (MRSA) in Canada. Between 2007 and 2011, 1266 MRSA were collected from inpatients and outpatients attending tertiary-care medical centres across Canada. Susceptibility testing was performed using broth microdilution and isolates were characterized by spa typing and PCR to detect the PantonValentine leucocidin (PVL) gene. Detection of heterogeneous vancomycin-intermediate S. aureus (hVISA) was performed using the Etest macromethod and confirmed by population analysis profiling. The annual proportion of S. aureus that were methicillin resistant decreased from 26.1 in 2007 to 19.3 in 2011 (P0.0002). Of 1266 MRSA isolated, 366 (28.9) were CA-MRSA genotypes and 868 (68.6) were HA-MRSA genotypes. The proportion of MRSA represented by CA-MRSA genotypes increased from 19.7 to 36.4 between 2007 and 2011 (P0.0001). CMRSA10 (USA300) was the predominant CA-MRSA genotype (22.1); the most common HA-MRSA genotype was CMRSA2 (USA100/800) (58.1). PVL was detected in 328/366 (89.6) of CA-MRSA genotypes and 6/868 (0.7) of HA-MRSA genotypes. The hVISA phenotype was detected in 7/27 (25.9) of MRSA with a vancomycin MIC of 2 mg/L. The most frequent CA-MRSA genotype was CMRSA10 (USA300), while CMRSA2 (USA100/800) was the predominant HA-MRSA genotype. Despite a decrease in the numbers of MRSA, the proportion of CMRSA10 (USA300) CA-MRSA has risen significantly between 2007 and 2011 in Canada.