Where does Clostridium difficile really come from?

It seems like half the people I know have sent me this article about Clostridium difficile for comment. It’s a news article about a New England Journal of Medicine research paper (Eyre et al 2013).

The paper has some interesting findings. They used whole-genome sequencing to look at the genetic makeup of C. difficile from infected patients in a hospital. It was an impressively comprehensive study that looked at samples from over 1000 patients. By looking at the DNA of C. difficile isolates from patients, they could see when the bacterium was likely passed between patients and when it was not. Over the 3 year study period, almost half of the C. difficile isolates were different enough genetically from other isolates to indicate they didn’t come from someone else in the hospital.

I don’t think it can be said with 100% confidence that all those C. difficile strains were truly acquired outside of the hospital (i.e. in the community), since they only looked at people with C. difficile infection. People can also carry the bacterium without any signs of disease, and it’s possible that such individuals were a source of infection for others in hospital. Since the researchers weren’t testing for subclinical carriers, they don’t know whether "unrelated" cases were from strains acquired outside the hospital or from undetected carriers in the hospital. I suspect a lot of cases truly do originate outside of the hospital, though, and this goes against current dogma that most hospital cases are acquired by spread between patients.

I think we're eating it all the time, probably from animals, and most of us get it and it doesn't matter."

  • I’ve been saying that for years. I think we probably ingest C. difficile every day from food, water and various environmental sources. Most often, it doesn’t cause of problem. Figuring out why it does in some situations needs to be a priority.

If you don’t look, you don’t find. It’s been a self-fulfilling prophecy for years with C. difficile:

  • People (supposedly) only get C. difficile if they’ve been in hospital on antibiotics.
  • If you don’t have those risk factors, you don’t get tested for C. difficile.
  • So... we never diagnose C. difficle in people who haven’t been in hospital or on antibiotics.

It’s been shown for many years (but often overlooked) that C. difficile may be a common cause of diarrhea in people in the general population and those without traditional risk factors.

more and more deep cleaning ain’t going to do any good.

  • (Not the typically grammatical approach for a University of Oxford researcher, but...) The point is that you can do everything to control C. difficile in the hospital and you still won’t be able to control all cases. I agree with that. However, care must be taken to ensure this doesn’t get translated into “most C. difficile is coming from outside the hospital anyway, so why should we spend so much time and money on cleaning and infection control?”

These findings have led some people to point the finger at animals as important sources of C. difficile.

  • I think this is taking the animal link too far. This is coming from someone who was one of the first and is still one of the few people to have looked at C. difficile in food. So if anything, I stand to benefit from any links between food and C. difficile (since more concern and more interest = more research opportunities).

Clostridium difficile expert Nigel Minton, from the University of Nottingham, had a nice balanced comment: "Obviously hospital infection control measures have had a big impact on C. difficile cases. But there is a growing feeling that community-acquired C. diff is equally important and there are also studies suggesting possible transmission to humans from animals. This has quite clearly been demonstrated from pigs to humans in the Netherlands."

  • I think this means that we need to pay attention to the potential role of animals, but not just dump the blame on them with no further study. The key point is we need proper research to figure out how C. difficile circulates in the community and what role animals, food, water and the environment play in transmission.

and “Nursing homes are a major factor as well, it is where you get a lot of people susceptible to infection."

  • That’s another interesting area and one that we’re currently investigation.
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