Characterization of methicillin-resistant Staphylococcus aureus in Canadian hospitals: 17 years of the CANWARD study...

This study reviewed the patient demographic parameters, molecular characteristics and in vitro antimicrobial susceptibility testing results for MRSA isolates infecting inpatients and outpatients presenting for care to tertiary-care Canadian hospitals between 2007 and 2023.

DNA sequencing was used to generate spa types. Panton-Valentine leukocidin (PVL) genes were detected by PCR. Broth microdilution antimicrobial susceptibility testing (CLSI M7, 12th edition, 2024) was performed with MICs interpreted by CLSI M100 breakpoints (34th edition, 2024) when available.

In total, 2697 MRSA were identified among 12734 Staphylococcus aureus isolates submitted to the CANWARD study between 2007 and 2023. The annual proportion of MRSA decreased significantly from 2007 (26.1%) to 2017 (16.0%) and then increased to 24.2% in 2023 (P < 0.0001). From 2007 to 2023, community-associated (CA)-MRSA spa types increased from 20.8% to 75.0% (P < 0.0001), while hospital-associated (HA)-MRSA decreased from 79.2% to 25.0% (P < 0.0001). The predominant MRSA spa types identified among all isolates were t002 (36.3%), an HA-MRSA genotype, and t008 (24.5%), a CA-MRSA genotype. PVL was detected in 36.0% of all MRSA isolates (76.3% of CA-MRSA; 2.7% of HA-MRSA). Percent susceptible values for all MRSA isolates were ≥99% for ceftobiprole, dalbavancin, daptomycin, linezolid, nitrofurantoin and vancomycin. Notable differences in percent susceptible values were identified for clindamycin (HA-MRSA, 38.9%; CA-MRSA, 86.9%) (P < 0.0001) trimethoprim/sulfamethoxazole (HA-MRSA, 91.4%; CA-MRSA, 98.8%) (P < 0.0001) and doxycycline (HA-MRSA, 96.6%; CA-MRSA, 98.8%) (P = 0.0003).

The changing epidemiology of MRSA in Canadian hospitals warrants continued national surveillance efforts as a resource to support therapeutic guidelines and infection control and prevention programmes.