An abstract in the upcoming European Conference on Clinical Microbiology and Infectious Diseases (ECCMID) has gotten a fair bit of press and led to a lot of questions because of some sensational headlines. I’ll hopefully be able to check out all the details at ECCMID (I’ll be there for the Global Leaders Group on AMR meeting), but let’s take a quick look at what we know so far…

First, we know there’s regular exchanging of bacteria between people and pets. That’s no surprise. We have close and prolonged contact with our pets, and many bacterial are adept at surviving in a variety of animal species in addition to humans. I’ve done various studies over the years looking at this with specific bugs like methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile.

There are some specific issues with certain bacteria, but there are also some common themes about how many of these bacteria behave:

  • Bacteria are periodically passed between people and pets, in both directions.
  • Bacteria may be more human-associated (e.g. Staphylococcus aureus) or dog-associated (e.g. Staphylococcus pseudintermedius), so when they move to another species, it’s often just a transient visit, such that they soon disappear again on their own.
  • If we look at multiple people and pets in the households, it’s typically more common to find human-associated bugs (like MRSA or C. difficile) in other humans, not pets.
  • When we drill down to see if the same strains of a bacterial species are present in both people and pets in a household, we often don’t find too much overlap.
  • Transmission of many concerning bacteria, particularly multidrug-resistant (MDR) bacteria that are most commonly associated with people, is probably mainly human-to-pet.

None of that is meant to dismiss the issue of transmission of MDR bacteria between people and pets. These strains that emerge and spread in people can spread to pets, and it’s possible for pets to spread them back under the right conditions. However, just finding the same bacterium in people and pets doesn’t mean the pet is an imminent risk. Much of the time, pets are innocent bystanders or victims, with humans being the source and posing a greater risk to other people that the pets. .

The ECCMID study, coordinated by Dr. Carolin Hackmann from Charite University Hospital Berlin, is a nice study of human-animal sharing of MDR bacteria. Here’s a summary of what we know so far about their work:

  • Researchers collected swabs from 2891 human hospital patients, 30% of whom harboured a resistant bacterium of some sort (no surprise).
  • Patients were then asked to submit fecal samples from their pets. Over 300 samples were collected from dogs and cats, of which 15% of dogs and 5% of cats harboured at least one resistant bacterium (no surprise there either, especially if they used a broad definition of a resistant bacterium).
  • In only four instances was the same bacterial species found in the human patient and their pet(s).
  • In only ONE instance (out of 2891 humans and over 300 pets) did a pet and person actually harbour the same bacterial strain, based on genomic testing. This was a MDR E. coli in a person and a dog.
  • In this one instance, nothing is reported in the press reports about directionality of spread. Presumably, there was no way to figure out who infected whom (or whether both person and dog were infected by someone/something else).

Was that dog a risk to other dogs or people? Potentially, just like many other dogs. The owner was probably a greater risk to others, but we can’t dismiss the potential for the dog to be a source of re-infection of the owner either (i.e. were the owner to get rid of the bacterium but then get re-exposed from contact with the dog).

It’s an interesting study and we need more work like this.

But, is this concerning?

Not really. It’s another piece of evidence that we live in a polymicrobial world as part of a vast ecosystem. Sometimes we share bacteria (and other microbes) with other members of that shared ecosystem. Usually, it’s benign; sometimes, it’s disastrous (i.e. SARS-CoV-2); and there are lots of gradations in between.

This doesn’t change my thinking or my behaviours, but adds one more piece of evidence to the notion that we have to look beyond people to control certain human diseases – something that is overlooked surprisingly often. At the same time, we need to maintain perspective and not over-react when we find certain microbes in pets that have close contact with people. There’s always going to be some infectious disease risk with any animal contact, but we can mitigate that risk significantly. When it comes to sharing MDR bacteria in households, the best things we can do are optimize health (both human and animal), improve antibiotic stewardship (to reduce the likelihood one of these bacteria will be present in any individual, human or animal), and use common sense basic infection control practices, like hand hygiene.

So, pay attention but don’t panic (and take headlines with a grain of salt).