Posted on April 8, 2009 by Scott Weese

Retrospective Study of MRSA in Horses

The April 2009 edition of the Equine Veterinary Journal includes a retrospective study of methicillin-resistant Staphylococcus aureus (MRSA) infections in horses (Anderson et al. 2009). This study looked at 115 horses with clinical MRSA infections (i.e. they weren't just colonized) from six different North American veterinary teaching hospitals. Here are some of the highlights (my comments are in italics):

  • The age range of affected horses was from "born in hospital" to 31 years old. Many different breeds were affected: Any horse of any age is susceptible to MRSA.
  • Community-associated (infections that likely originated on a farm) and hospital-associated (infections that likely originated in a veterinary hospital) were equally common. MRSA is not just associated with veterinary hospitals, and must be considered even when there is no history of hospitalization. I suspect that overall, many more MRSA infections occur on farms than in equine hospitals.
  • Surgical site infections were most common in hospitalized horses, accounting for 58% of infections. No big surprise here. It makes sense because of the trauma associated with breaking the body's normal protective barriers (e.g. making a surgical incision in the skin) and probably other issues like antibiotic treatment, stress and contact with lots of hospital  personnel.
  • Skin and soft tissue infections accounted for 29% of infections that originated on farms. This also isn't surprising - these types of infections are most common in community-onset infections in people as well.
  • Joint infections accounted for 18% of community-associated infections. This surprised us and is a concern, because joint infections (of any kind) can be very severe. Detailed information about these infections wasn't available, but some of these could have been associated with accidental contamination of joints during joint infections.
  • 84% of horses with MRSA infections survived. This is a very important finding. It shows that MRSA is a survivable infection in most cases. Prompt and proper treatment are the key.

People shouldn't panic when they hear "MRSA", but the importance of prompt diagnosis through culture of possibly infected sites can't be emphasized enough.  More information about MRSA in horses can be found on the equIDblog Resources page.

Photo: Skin and soft tissue infection (SSTI) of a horse's leg caused by Staphylococcus aureus.
 

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