Objective: To evaluate the prevalence of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) in horses and horse personnel.
Design: Prospective prevalence study.
Sample population: 972 horses and 107 personnel from equine farms in Ontario, Canada and New York state.
Procedure: Nasal swab specimens were collected from horses and humans on farms with (targeted surveillance) and without (nontargeted surveillance) a history of MRSA colonization or infection in horses during the preceding year. Selective culture for MRSA was performed. Isolates were typed via pulsed-field gel electrophoresis, and antibiograms were determined.
Results: MRSA was isolated from 46 of 972 (4.7%) horses (0/581 via nontargeted surveillance and 46/391 [12%] via targeted surveillance). Similarly, MRSA was isolated from 14 of 107 (13%) humans (2/41 [5%] from nontargeted surveillance and 12/66 [18%] from targeted surveillance). All isolates were subtypes of Canadian epidemic MRSA-5, an uncommon strain in humans. All isolates were resistant to at least 1 antimicrobial class in addition to beta-lactams. On all farms with colonized horses, at least 1 human was colonized with an indistinguishable subtype. For horses, residing on a farm that housed > 20 horses was the only factor significantly associated with MRSA colonization. For humans, regular contact with > 20 horses was the only identified risk factor.
Conclusions and clinical relevance: Results confirm a reservoir of colonized horses on a variety of farms in Ontario and New York and provide evidence that 1 MRSA strain is predominantly involved in MRSA colonization in horses and humans that work with horses.