You Can't Test Yourself Out of an Outbreak

They say you can’t test your way to food safety, and similarly you can’t test yourself out of an outbreak. However, this is exactly the message being sent by officials in Colorado who advertise that “Beef patties test negative for E. coli at CDA lab.” In the popular press and even within some food safety discussion online, this seems to be the basis for exonerating ground beef as a suspect in a recent E. coli O157:H7 outbreak. I am not suggesting that FDA and CDC’s focus on onions is incorrect. Rather, I’m saying that it’s dangerous to state that the testing is the reason that beef is not a suspect.

I’m less concerned about the message this sends to consumers and more concerned about the message it sends to the industry. Does it suggest that a positive test is required to say that something is associated with an outbreak? Since the outbreak strain was not found in onions, does it mean that they aren’t associated with the outbreak either?

An even more recent (different) outbreak also references product testing, which, in my opinion, is a more accurate representation of the limitations of testing:  "A negative test result for the lettuce does not conclusively rule out the salad as the source of the E. coli outbreak," the St. Louis County Health Department said. "This is because bacteria like E. coli often occur in isolated pockets within food products, making it possible for a sampling event to miss the pathogen entirely ... A negative result does not necessarily indicate the absence of the bacteria …"

I’ve met many food industry members who believe that testing is the be all, end all. In other outbreaks, some have argued that a particular product could not possibly be associated with illness (despite strong traceback and epi data) since a positive test result was never found. Saying that a product tested negative and therefore is cleared of suspicion is the other side of that coin.

Testing is a game of statistics, and in the case of outbreaks is also a game of timing since by the time an outbreak is identified, the product of interest may have already exited the supply chain. Unless 100% of product is contaminated, testing is no guarantee that some low level of contamination isn’t still lurking. Testing is like a game of Russian Roulette: just because the shot didn’t fire doesn’t mean there isn’t a bullet in the gun.

A positive test result is affirmative: it’s a clear signal. A negative result (even a few negatives) doesn’t mean much. In my opinion, industry relies too heavily on negative test results as confirmation that food safety is being well managed. To see some agencies place a similar emphasis on negative test results is pretty shocking and disappointing.

To learn how to make the most of your testing program as part of your overall preventive food safety system, reach out.