Epidemiologist explains how cyclospora test on lettuce sample might have resulted in false positive

[00:00:00]There are new questions surrounding the source of the parasitic Cyclospora outbreak that has impacted thousands of people across the country. The Food and Drug Administration says the sample of lettuce from Taylor Farms was actually a false positive, but the FDA says that does not change the basis for its investigation or the quote overwhelming data supporting the current voluntary recall by Taylor Farms. Several chains including Taco Bell have been linked to the outbreak. Let's bring in Ben Miller.

[00:00:27]He's an epidemiologist with more than 25 years of experience investigating and responding to foodborne illness outbreaks. Thank you so much for being here. Help us understand how a false positive can happen.

[00:00:39]>> Yeah, absolutely. You know, it's a little bit surprising to see that announcement from FDA and then see that kind of reverse in the same day yesterday. And you know, what can happen when you're testing this type of material is these tests aren't 100%. You know, what we see on TV sometimes is you know, you take a test and it's always definitive. Things can go wrong. Not enough genetic material can be there.

[00:01:00]You can get cross-reaction with other genetic material and that's really what those tests are looking for. They're looking for is the genetic material Cyclospora there? And so while there are steps that can go wrong, there are steps in that process too that should catch that. So it it was a little surprising to see the agency make that announcement and then walk that back.

[00:01:19]>> Yeah, and so then what do they What does it mean that the data is overwhelming and still supports the recall?

[00:01:26]>> So it's important to understand, you know, what happens in an investigation like this. And I started my career 25 years ago as a graduate student working on something called team diarrhea. We were a group of students that would call people who got sick. So the way an investigation like this works is somebody eats something and then there's a certain amount of time between the time you eat something and the time you become ill. And with Cyclospora that can actually be a long time. That can be two days all the way up to 14 days. And that's one of the things that makes an investigation like this challenging.

[00:01:58]And then somebody goes to a doctor and gets interviewed or admitted maybe to take a stool sample, and then it's a few more days or weeks before the public health department might call them and ask them about their potential exposures.

[00:02:09]All of that time adds up, and so it takes sometimes a long time to pick up the signal that might be a common source of an outbreak. In this case, because we have so many cases, you know, there's over 6,000 cases of illness that have been identified in Michigan, that we're able to identify most of those people would have had some type of exposure to lettuce at a Taco Bell.

[00:02:33]That's when FDA gets involved. They start what's called a traceback investigation. They look at where did that lettuce come from? Is there a common source? Could that explain the outbreak that's going on? So, all of that takes time, but when you start to stack that evidence up, you start to paint a clear picture of like it's probably this or it's probably this. And and that's where we are right now, even setting aside this false positive.

[00:02:56]>> Okay, that is very helpful. So, we're not necessarily back at square one.

[00:03:00]Like, how long do you think it'll take until we have some answers? And you as an epidemiologist, are you changing any of your habits?

[00:03:08]>> Yeah, that's a great question. I I don't think we're back at square one. I think the epi on this particular outbreak of cyclospora is strong. I think FDA has done a good job figuring out what that probable source is, and we've seen, you know, the company involved, Taylor, do a recall. So, they feel like, you know, the evidence was strong as it was presented to them by FDA and the public health authorities. You know, from my standpoint, we do know that imported produce is of higher risk and associated with cyclospora. That just tends to be where it happens. It's endemic in the population, and you know, the way we control cyclospora is if harvest and when that product's being grown, by and large, it's harder to control it once it gets into the supply chain. So, from my standpoint, personally, I haven't changed a lot of my habits because when we look at where those cases are, I think we have a good sense of where those outbreaks are occurring. You know, but I think if consumers are concerned, you can always remove outer leaves from lettuce, things like romaine. Washing is somewhat effective, but that that Cyclospora is a little bit sticky and it will stick to certain produce surfaces.

[00:04:10]So, knowing where your produce comes from this time of year is is one thing that can help consumers generate awareness.

[00:04:17]>> Ben Miller, thank you so much.

[00:04:20]>> Absolutely.