backyard chickenA reasonable question, expanding on the recent discussion about urban chickens and disease risks, is: why don’t we know how often people get sick from urban chickens?

To answer the question, we need to think about how diseases are diagnosed and reported.

Let’s say I decide to raise some chickens in my backyard. (Very hypothetical since it’s not going to happen. Raising chickens at my place would simply be creating a poultry buffet for coyotes and foxes, but let’s pretend.) If I get a disease from them, who will find out?

Here’s what’s involved if I get Salmonella from my imaginary chickens.

  • I have to get sick (the easy part)
  • I have to be sick and/or motivated enough to go to a doctor.
  • The doctor has to ask for a fecal sample for testing.
  • I have to actually collect the sample and drop it off.
  • The lab has to grow Salmonella from the sample.
  • That gets reported to Public Health.
  • Public Health investigates and finds out I have chickens.

Then what? Even if all these steps occur, which happens in the vast minority of cases, will this be tracked?

Probably not.

I would be a single case on a line-listing of people with salmonellosis. Single events like this tend not to attract much attention. Typically, attention is paid to situations where the same strain of Salmonella is isolated from a lot of people or where a lot of people get sick at once. Sporadic disease doesn’t get the same attention (for good reasons). Disease caused by a range of different strains also gets less attention since it’s unlikely to have a common source that needs to be addressed. In the study I talked about in Part I, there were 31 distinct Campylobacter types among the 72 samples, showing how much diversity can be present.

So, there could be a lot of people getting infected with Salmonella, Campylobacter or other zoonotic pathogens from backyard chickens. Or there could be none.

Reality is probably somewhere in the middle. Unless someone specifically goes searching for backyard chicken-associated disease (and has access to databases to do this), we won’t know. Even then, without knowing much about how common backyard chickens are, putting results into context is difficult.

If there are 4 infections identified by a health unit in a summer, what does that mean?

  • If it’s 4 infections from 4000 houses with chickens, that’s different than if it’s 4 infections from 8 houses with chickens.
  • It’s also much different if it’s 4 chicken owners vs 4 neighbours of chicken owners (who didn’t choose to have chickens).

As is common, a lack of good data doesn’t help the decision-making process.