Comparison of Community‐Associated and Health Care‐Associated Methicillin‐Resistant <i>Staphylococcus aureus</i> in Canada: Results from CANWARD 2007

Abstract

BACKGROUND: Community‐associated methicillin‐resistant Staphylococcus aureus (CA‐MRSA) differ from health care‐associated MRSA (HA‐MRSA) in their genotypic and phenotypic characteristics. The purpose of the present study was to compare the demographics, antimicrobial susceptibilities and molecular epidemiology of CA‐MRSA and HA‐MRSA in Canada. METHODS: In 2007, 385 MRSA isolates were collected from Canadian patients attending hospital clinics, emergency rooms, medical/ surgical wards and intensive care units. Susceptibilities to betalactams, clarithromycin, clindamycin, daptomycin, levofloxacin, linezolid, moxifloxacin, tigecycline, trimethoprim‐sulfamethoxazole and vancomycin were determined by Clinical and Laboratory Standards Institute broth microdilution. Strain typing was performed by pulsed‐field gel electrophoresis (PFGE) and the mec A, nuc and pvl genes were detected by polymerase chain reaction. RESULTS: Of the 385 MRSA, 19.5% were CA‐MRSA and 79.2% were HA‐MRSA as determined by PFGE. CA‐MRSA belonged to PFGE types CMRSA10/USA300 (66.7%) and CMRSA7/USA400 (33.3%); PFGE types identified among HA‐MRSA included CMRSA2/USA100/800 (81.6%), CMRSA6 (13.1%), CMRSA1/ USA600 (3.3%), CMRSA5/USA500 (1.3%), CMRSA3 (0.3%) and CMRSA9 (0.3%). Panton‐Valentine leukocidin (PVL) was detected in 94.7% of CA‐MRSA and 0.7% of HA‐MRSA. Resistance rates (CA‐MRSA versus HA‐MRSA) were 61.3% versus 97.7% to levofloxacin, 73.3% versus 96.7% to clarithromycin, 12.0% versus 74.8% to clindamycin and 0.0% versus 15.4% to trimethoprim‐sulfamethoxazole. No MRSA were resistant to vancomycin, linezolid, tigecycline or daptomycin. CONCLUSIONS: CA‐MRSA represented 19.5% of all MRSA. CA‐MRSA was significantly more susceptible to levofloxacin, clarithromycin, clindamycin and trimethoprim‐sulfamethoxazole than HA‐MRSA. Of CA‐MRSA, 94.7% were PVL‐positive while 99.3% of HA‐MRSA were PVL‐negative. CA‐MRSA is an emerging pathogen in Canadian hospitals.