Discussion

Steinman, A., Navon-Venezia, S., Tirosh-Levi, S., Masarwa, S., Adler. A., Chmelnitsky, I., Carmeli, Y., Klement, E., Schwaber, M. J.
Aims: To describe a methicillin-resistant Staphylococcus aureus (MRSA) outbreak in a veterinary teaching hospital. Methods: Swabs were collected from 84 hospitalised horses and from 139 people. Identification and antimicrobial susceptibility testing was performed by VITEK2. Genetic relatedness of strains was determined by spa typing. An infection control intervention was implemented which included testing and isolating MRSA positive carrier horses and decolonisation of MRSA positive carrier personnel. Results: MRSA was isolated from 12 horses, in 6 of which MRSA was isolated from post surgical wound infections. MRSA was isolated from 16 people. Ten of the 20 full-time workers of the large animal department were MRSA nasal carriers. Isolates were compared by phenotype and molecular characteristics. Among the horse isolates, all had a multi-drug resistance (MDR) phenotype and all were spa t535. Among the human isolates, most (87.5%) had the MDR phenotype and were spa t535. Six months later nasal swabs were collected from all large animal department personnel, from all MRSA carriers and from all hospitalised horses and all were MRSA negative. Conclusions: During this outbreak cross-transmission of a rare MRSA clone occurred between horses and people at a veterinary teaching hospital. Intensity of exposure to hospitalised horses was associated with likelihood of staff carriage. An infection control intervention succeeded in eradicating carriage at 6 months post intervention. Practical significance: Equine practitioners are at increased risk for nasal carriage of MRSA. Strict protocols should be implemented in order to reduce the risk for contamination. Currently, every hospitalised horse is sampled for MRSA nasal carriage at the time of admittance, one week after hospitalisation and at the time of discharge. MRSA-positive horses are quarantined and are treated using precautions. We believe these practices will decrease the risk for human infection and will also reduce the risk for horse to horse transmission.