MRSA Surveillance in Horses at a Veterinary Teaching Hospital

Screening for methicillin-resistant Staphylococcus aureus (MRSA) upon arrival to a veterinary hospital is useful for detecting cases of the "superbug" early so affected horses can be isolated, said Scott Weese, DVM, DVSc, Dipl. ACVIM, an associate professor at the University of Guelph's Ontario Veterinary College (OVC). This practice reduces the chance that the emerging antibiotic-resistant zoonosis (disease transmissible from a non-human animal to humans) will be spread to horses and personnel.

Weese said OVC detected its first case of MRSA in 2000. Since then, he and colleagues have made it policy to swab the nasal passages of every horse admitted to the hospital. Weese presented an abstract on MRSA data collected between Oct. 4, 2002, and June 15, 2004, at the annual meeting of the American College of Veterinary Internal Medicine (ACVIM) held June 1-4 in Baltimore, Md.

"Screening programs are very important in human hospitals," said Weese, saying OVC took their lead. "Every horse at OVC gets swabbed coming in, weekly, and leaving." Not only does this allow for isolation of infected horses, it differentiates community-acquired (picked up outside the hospital) from nosocomial (caught in the hospital) infections.

Hospital personnel swabbed 2,283 of 3,056 admitted horses (74.7%) at least once in the study. MRSA was isolated from 120 of the 2,283 (5.3%). Of those, 61 (50.8%) were community-associated and 53 (44.2%) were nosocomial. The origin of six of the infections was unclear. Clinical infections (including anything from septic arthritis to an incision or wound infection) were present or developed in 14 of the 120 horses (11.7%).

In looking at risk factors, horses with community-acquired MRSA positives were more likely to develop clinical signs than horses that acquired MRSA during their stays at the hospital. Only four (7.5%) of the hospital-acquired cases developed clinical infection, an incidence rate of 1.8 per 1,000 admissions.

"Over the last year, there's been a dramatic drop in community-acquired cases," said Weese. Using infection control methods, particularly frequent screening of horses and people, and isolation of colonized horses, the bug has been eradicated from several horse farms where carriers were found, and it has pushed farm owners to examine their infection control practices. "Low infection rates are good to see, but without screening we could be missing carriers that could silently spread MRSA for future problems." he added.

In conclusion, Weese said this study showed MRSA screening is feasible, beneficial, and has given veterinarians a better awareness of MRSA risk during hospitalization.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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