three-dogsI’ve written about this many times (probably because I get asked about it almost every day), but there’s not really a simple answer to the question “Does methicillin-resistant Staph. pseudintermedius pose a human health risk?

My typical answer is along the lines of “Yes, but…” with discussion about how rare Staph pseudintermedius (SP) infections are in people, despite widespread exposure to infected or colonized dogs. However, “low” doesn’t mean “no.”

A recent article in Vector-Borne and Zoonotic Diseases (Lozano et al 2017) describes methicillin-susceptible SP infections in four people. The first question you might have is, why would I talk about susceptible SP in the discussion of MRSP?  It’s relevant because they’re still the same bug – being methicillin-resistant doesn’t make SP more likely to infect a person, but it does make it harder to kill if it causes an infection (which is why it’s a concern). Therefore, understanding aspects of susceptible SP infections is useful in understanding MRSP.

Here are some highlights from the study:

  • Infections were diagnosed in four people in a hospital in Spain over a 10 month period. All four patients had what sounds like relatively straightforward skin and soft tissue infections. Two of the four people were higher risk (one with cancer and one described generically as being immunocompromised).
  • One patient had a surgical site infection and no contact with animals. Not much more is said about this one but is raises questions about where it might have originated.
  • Patient 2 had contact with dogs, but did not own any herself. Patients 3 and 4 both owned dogs.
  • SP was isolated from the 3 dogs owned by patients 3 and 4. That’s not surprising since we can find SP in most dogs at any given time.
  • The same SP strains were found in dogs and infected people within the same households. That’s also not surprising since the dogs were the logical source and we’ve previously shown that when we find S. pseudintermedius in people in households, it’s usually the same strain as in their pet. Most likely, we interchange SP and various other bacteria on a regular basis.

In some ways, this is just a straightforward but nicely documented small series of SP infections in people. It doesn’t change the answer to the “Is MRSP zoonotic?” question that I’ll probably get (again) at some point over the next couple of days. However, it re-inforces the low but ever-present potential risk posed by this bacterium, like many other bacteria that dogs carry.

One final comment to hopefully put things into perspective: When talking about MRSP risk, a statement I often make is “If I had to rank the top 5 zoonotic risks posed by a dog carrying MRSP (or plain old SP), MRSP/SP would probably not make that list.” It’s worth paying attention to MRSP, but at the same time, it’s important to keep it in perspective, realize how rare it is, realize how basic measures probably reduce that risk even further, and remember that all dogs pose some (very low) degree of risk, and we’re better off thinking about routine practices rather than focusing on low risk bugs like this.

For me, this report is just one more reason to emphasize the overall message: the risk is low but you never want a multidrug-resistant infection so you should use some basic infection control and hygiene measures to reduce exposure to MRSP. Most of that is easy, revolving around avoiding contact with infected site (eg. skin infections), avoiding contact with the nose, mouth and feces of dogs with MRSP infections (since they are often carrying the bug at those sites as well) and good old handwashing.