A reader has been trying to post a question about an older post on C. difficile in visitation dogs. Here’s the question and my answer:

Do the dogs have a risk of getting sick from the C. difficile bacteria?  I understand from the post that they can ingest and shed it in their feces, but the post never states whether they can get sick from the bacteria or not!

It’s a great question, and it lacks a similarly great answer. We don’t really understand C. difficile in dogs. We’ve made an association between the presence of C. difficile toxins in feces and the presence of diarrhea in dogs, but there are a few things that cloud our understanding of whether C. difficile is actually a significant problem. My guess is that C. difficile is a cause of diarrhea in dogs, but it’s not a major one. Or, maybe more accurately, it’s not a common cause of serious disease. It might be a relatively common cause of mild disease that gets better on its own (and therefore just doesn’t get diagnosed), but is an uncommon cause of serious disease. Dogs don’t get recurrent C. difficile infection or pseudomembranous colitis like people do, and those are the two most serious and recognizable forms of disease. Given the commonness of exposure (dogs probably ingest a small number of C. diff spores on a routine basis) and the low apparent incidence of disease (at least serious disease), it doesn’t seem to be a major health risk.