Comparison of Community-Associated and Health Care-Associated Methicillin-ResistantStaphylococcus aureusin Canada: Results from CANWARD 2007

BACKGROUND: Community-associated methicillin-resistantStaphylococcus aureus (CA-MRSA) differ from health care-associatedMRSA (HA-MRSA) in their genotypic and phenotypic characteristics.The purpose of the present study was to compare the demographics,antimicrobial susceptibilities and molecular epidemiology ofCA-MRSA and HA-MRSA in Canada.METHODS: In 2007, 385 MRSA isolates were collected fromCanadian patients attending hospital clinics, emergency rooms, medical/surgical wards and intensive care units. Susceptibilities to betalactams,clarithromycin, clindamycin, daptomycin, levofloxacin,linezolid, moxifloxacin, tigecycline, trimethoprim-sulfamethoxazoleand vancomycin were determined by Clinical and LaboratoryStandards Institute broth microdilution. Strain typing was performedby pulsed-field gel electrophoresis (PFGE) and the mecA, nuc and pvlgenes 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 toPFGE types CMRSA10/USA300 (66.7%) and CMRSA7/USA400(33.3%); PFGE types identified among HA-MRSA includedCMRSA2/USA100/800 (81.6%), CMRSA6 (13.1%), CMRSA1/USA600 (3.3%), CMRSA5/USA500 (1.3%), CMRSA3 (0.3%) andCMRSA9 (0.3%). Panton-Valentine leukocidin (PVL) was detectedin 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% toclindamycin and 0.0% versus 15.4% to trimethoprim-sulfamethoxazole.No MRSA were resistant to vancomycin, linezolid, tigecycline ordaptomycin.CONCLUSIONS: CA-MRSA represented 19.5% of all MRSA.CA-MRSA was significantly more susceptible to levofloxacin,clarithromycin, clindamycin and trimethoprim-sulfamethoxazole thanHA-MRSA. Of CA-MRSA, 94.7% were PVL-positive while 99.3% ofHA-MRSA were PVL-negative. CA-MRSA is an emerging pathogenin Canadian hospitals