Dog licking man's face

Letting a dog lick your face is considered high-risk behavior in the world of dog-transmitted Staph pseudintermedius

Here’s a potpourri of reports of staphylococcal infections in humans linked to dogs. Specifically, they’re infections caused by Staphylococcus pseudintermedius, a common dog-adapted species of Staphylococcus. (If you get freaked out reading these, make sure you read the end of the post so you also get the context.)

A 41-year-old man with a history of skin disease and receiving parenteral nutrition (i.e. being fed intravenously) presented with fever, and developed a recurrent infection of the access port of his indwelling intravenous catheter. Staph pseudintermedius was isolated from him and his dog. They recommended he get rid of his dog.

• It doesn’t sound like they recommended any other infection control measures, and the person did not get rid of the dog initially. He later did, after being hospitalized from the infection.
• It’s impossible to say, but I suspect there were other (better) ways to reduce the risk of transmission in the household rather than have the patient get rid of his pet, especially if the dog was an important part of his life.

A hemodialysis patient with an indwelling intravenous catheter developed a S. pseudintermedius infection.

• The authors stated, “Catheter care education should include information about pet exposure and the possibility of zoonotic infections.” I can’t access (aka I’m too cheap to spend the $37 access fee for) the full paper, so I couldn’t see what details were provided.

Infection of an implanted port catheter system by methicillin-resistant S. pseudintermedius (MRSP). MRSP is basically the dog version of methicillin-resistant Staphylococcus aureus (MRSA).

• The MRSP strain was a type that’s commonly found in dogs internationally.
• The person was a dog owner, but they didn’t investigate the pet dog and they don’t say anything about infection control measures in the paper.

A 56-year-old woman with rheumatoid arthritis, osteoporosis and common variable immunodeficiency developed a S. pseudintermedius infection of bone and soft tissue after surgery to repair a broken arm.

• The same bacterial strain was subsequently also isolated from the patient’s pet dog.
• No high-risk behaviours (e.g. dog licking face or broken skin, dog sleeping in the bed) were reported.
• The patient had another dog that had a septic tooth and was being treated with an antibiotic, but it died before they were able to get samples. There’s no more discussion of that, but I wonder whether she was the one giving the dog oral medications and had exposure to the dog’s saliva that way. It’s possible the sick dog harboured the same bacterium as its housemate… maybe even more likely, since antibiotic treatment is a risk factor for MRSP in dogs. That’s all highly theoretical, obviously.

A 39-year-old woman receiving peritoneal dialysis developed septic peritonitis (i.e. infection of the abdominal cavity) with (you guessed it) S. pseudintermedius.

• Peritoneal dialysis (PD) uses an indwelling catheter that goes from the skin into the abdomen.  Infections are the main complication associated with these devices.
• The patient had a dog that slept in her bed, having close contact with the dialysis catheter.
• While vague, the authors did address basic infection control issues: “No recurrent infections have been noted since admission with better hygiene and some distance with the pet dog.” and “Furthermore, PD training and ongoing education programs are needed for pet owners to help decrease the risk of PD-associated bacterial peritonitis. “
• That’s what I want to see – awareness and education, not ignoring the issue or knee-jerk recommendations to get rid of the pet.

The main take-home message from all this: Relax, and wash your hands.

Is S. pseudintermedius a bigger threat now than in it was years ago?

• No. It’s not likely any more able to infect people than it could in the past. Most dogs harbour the bacterium on their skin and/or in their mouth, nose and intestinal tract. Millions of people are exposed it every day. Yet, infections are very rare. It’s something to be aware of but we shouldn’t over-react.

But there are many more reports of human disease caused by S. pseudintermedius. Are zoonotic infections increasing?

• Probably not. I suspect it’s a function of better identification of the bacterium by human diagnostic laboratories (they could have misdiagnosed it as a common human staph in the past), and proliferation of journals that will publish single case reports. I’d wager it’s more of an increase in publications than an increase in disease.

Is MRSP from dogs a bigger threat now?

• Sure, because it’s much more common in dogs than it used to be.
• However, MRSP is no more likely to spread to people than susceptible S. pseudintermedius, it’s just harder to kill when we have to treat it. It’s an important bug but human infections seems to be rare.
• We can’t ignore MRSP, but it likely doesn’t crack the top 10 list of things I’m concerned about your average dog and cat transmitting to a person.

So, what should we do?

Staphylococcus pseudintermedius is a bug that’s found in and on most dogs. Most of the time, it doesn’t do anything to us when we encounter it. We have barriers like our skin and immune system to fight off such foreign invaders. When those barriers are compromised, the risk of infection goes up. Preventing infections comes down to very basic precautions like:

• Hand washing
• Limiting contact with saliva, nasal secretions and feces.
• Keeping open wounds or invasive devices (like catheters) away from animals, and in particular, their secretions. (For me, here’s where there’s a difference between sleeping in the bed and sleeping on the bed. I’m ok with an animal sleeping on the bed if there’s no direct contact with the person. If it’s sleeping under the covers with someone, that creates ample, long-term contact for transmission of pathogens.)
• Good, prompt wound care after any bite or scratch.

One last thing that often gets forgotten: People should make sure their physician knows they have contact with animals, and physicians should ask about animal contact. Most of the time it’s not relevant, but it only takes a few seconds and can provide important information in certain cases.

More information about MRSP can be found on the Worms & Germs Resources – Pets page.

Reprinted with permission from Worms & Germs Blog