It’s been quite a while since the last post about MRSA in horses, but rest assured, it’s still out there!  Not too surprisingly it’s also spreading (or at least starting to be found) in new places.  A recent report in Veterinary Microbiology (Schwaber et al, 2013) describes an MRSA outbreak at a large animal teaching hospital in Israel.  It is the first report of MRSA colonization in horses in the Middle East, although it’s possible (and quite likely) that there’s more to be found.

The discovery of the problem had a pretty typical progression: there were two horses in the hospital with post-operative wound infections from which Staphylococcus aureus was cultured, and the isolates from both horses had similar antimicrobial resistance patterns, including resistance to all beta-lactam antimicrobials (= MRSA). Validly concerned about the potential for the MRSA to spread among horses and people in the hospital, an investigation ensued – in this case the National Center for Infection Control (NCIC) was actually called in to coordinate the operation.

• They found MRSA in 12/84 (14.3%) horses, of which 11 were in the hospital at the time of sampling, and 1 had recently been discharged from the hospital.  Consider though that 44 of the horses sampled were simply from farms from which an MRSA-positive horse had come – so 11/40 horses in the hospital were positive – that’s 27.5%!
• 16/139 (11.5%) of personnel at the teaching hospital were positive for MRSA.  Fortunately there were no clinical MRSA infections reported in people.
• The MRSA strain that was found in all the horses and most of the people was a very rare type – not the usual sequence type 8 (ST8) we’re used to finding in horses in various other parts of the world.  This one was an ST5, spa-type t535, SCCmec type V, which is even rare in the human population.
• The primary action taken to get the outbreak under control: increased infection control measures, including isolation of infected and colonized horses which were then handled with contact precautions (e.g. gloves, gowns), discharging horses from hospital as soon as medically possible to decrease transmission pressure, and having a nurse from the NCIC come in to instruct personnel on the measures to be taken, including emphasis on hand hygiene and increased use of alcohol-based hand sanitizer.
• In this outbreak, decolonization therapy was prescribed for all colonized personnel.

The report does not mention whether or not personnel at the hospital were required to submit to being tested and undergoing decolonization therapy.  This can be a very tricky issue to handle, and it depends on what the local laws are.  In Canada, employees cannot be forced to undergo testing or treatment, but in some other countries MRSA-positive healthcare workers may not be allowed to even work until their carrier status is cleared.

Interestingly enough, just a year or two before this outbreak occurred a study (as yet unpublished) had been carried out in the same region, during which they found MRSA in 7.2% (6/83) of hospitalized horses and none in horses from local farms.  There is no mention regarding whether or not the hospital had taken measures to eradicate MRSA from the facility before the clinical infections that triggered the outbreak investigation occurred.

This was a typical MRSA "iceberg" – a couple of clinical cases were triggers for an investigation that found a lot more horses and people were actually carriers.  This is exactly why it’s important to remain diligent about infection control measures like hand hygiene at all times, so that pathogens like MRSA don’t move in "under the radar."  The authors of the paper summed it up nicely (although I’d leave out the part about decolonization):

"Strict implementation of hand hygiene, isolation of colonized and infected horses, decolonization
of colonized personnel and above all, constant education of veterinary students and personnel about the importance of infection control measures are required in order to decrease the risk for colonization and infection of both horses and personnel by MRSA and other pathogens."

More information about MRSA in horses is available on the Worms & Germs Resource – Horses page.