Regional Changes in Methicillin-Resistant Staphylococcus aureus in Purulent Skin and Soft Tissue Infections among Patients Presenting to Canadian Emergency Departments
Community-associated methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a leading cause of purulent skin and soft tissue infections (SSTI) in many areas of the world. The evolving epidemiology of MRSA in SSTIs across Canada is seldom described. This study characterizes the changing prevalence and microbiology of MRSA in patients presenting to emergency departments (EDs) across Canada over half a decade.
Using a prospective, observational design, we enrolled patients presenting to 27 hospital EDs (spanning 7 provinces) with acute purulent SSTIs over 3 phases: P1 - 7/1/2008 to 4/30/2009; P2 - 1/16/2012 to 11/30/2012; and P3 - 4/28/2013 to 3/31/2014. Participating EDs agreed to collect wound swabs on all patients presenting with purulent SSTIs. Eligible patients were those whose wound cultures grew S. aureus. Antimicrobial susceptibility testing by broth microdilution in accordance with CLSI guidelines was undertaken on all isolates. Structured chart audits were undertaken. Simple proportions are reported at site, regional and provincial levels and compared using Chi-squared/Fisher exact test, as appropriate.
A total of 4752 (P1: 1340; P2: 1622; P3: 1790) S. aureus positive encounters were recorded over the 3 phases. Accounting for all sites, the overall MRSA prevalence decreased significantly between P1 (31%) and P2 (27%, p=0.002), and remained unchanged in P3 (28%, p=0.42). A similar trend was observed among the 12 sites that participated in all 3 phases (P1 vs. P2: p=0.004; P2 vs. P3: p=0.70). Among the 18 sites participating in at least two study phases, most (61%) experienced a declining trend in MRSA prevalence, while 28% of them observed an increase (3 Ontario and 2 Alberta sites). City-level analyses revealed variability in the MRSA prevalence. Most cities experienced a decrease in the prevalence. Overall, the highest prevalence was seen in the western provinces of British Columbia (P1: 44%, P2: 66%, P3: 53%), Saskatchewan (P2: 47%, P3: 48%), and Alberta (P1: 48%, P2: 28%, P3: 31%) during all phases, while the lowest prevalence was observed in Quebec (P1: 20%, P2: 19%, P3: 11%).
MRSA epidemiology continues to evolve across Canada. While the overall Canadian prevalence of MRSA in SSTIs remains substantial, it is variable across the country, and appears to be decreasing regionally.
B. H. Rowe, None
B. Willey, None
V. Porter, None
A. E. Simor, None
A. Mcgeer, None
M. Loftus, None
K. Katz, None