FDA keeps lettuce focus in Cyclospora probe after false positive

The Food and Drug Administration said Monday that a false positive in its Cyclospora testing has not changed its view that shredded iceberg lettuce from Taylor Farms locations in central Mexico is tied to an outbreak that has sickened more than 1,600 people. The investigation has already produced product removals across restaurants and retailers, while Placer.ai data cited by CNBC showed Taco Bell traffic down about 19% on Friday versus its day-of-week average so far this year.

The FDA said Sunday that a sample of iceberg lettuce supplied by Taylor Farms de Mexico had initially appeared to contain the parasite but was later determined to be a false positive. The agency said that result applied to one shipment and did not alter its broader traceback findings or its advice that consumers avoid recalled iceberg lettuce.

What the FDA says changed

In foodborne illness investigations, screening tests can produce a preliminary signal that later confirmation testing does not reproduce. Doctors cited by CNBC said Cyclospora can be difficult to replicate in laboratory conditions, making the interpretation of test results more complex.

The FDA said its investigation and outbreak data still point to shredded iceberg lettuce from Taylor Farms operations in central Mexico. The agency has said some of that lettuce was served at Taco Bell restaurants. CNBC reported that the FDA had not responded to questions about whether additional suppliers or ingredients are being examined or whether more guidance is expected.

Cyclosporiasis can cause gastrointestinal symptoms that last days or weeks. Former FDA Commissioner Dr. Scott Gottlieb told CNBC the false positive does not sever Taylor Farms’ connection to the outbreak. He said the recalled product was imported weeks earlier and was separate from the lettuce sample that produced the disputed test result.

Gottlieb also said investigators need to examine multiple shipments because Cyclospora can take up to two weeks to incubate and lettuce has a short shelf life. That timing can make it difficult to match illnesses to a specific load of produce, even when shipments come from the same farm or supplier network.

Retailers and restaurants pull products

Taylor Farms said Monday that it would continue its voluntary recall of implicated iceberg lettuce from central Mexico. Taco Bell said it had begun removing suspected lettuce from restaurants in affected states and told CNBC that it had taken the product out of relevant locations within 72 hours of starting the process.

Walmart said Monday it had removed four Marketside bagged salad kit products supplied by Taylor Farms from stores in 27 states as a precaution. The retailer said there was no indication that those products were part of the outbreak and that no illnesses had been confirmed in connection with them.

The Michigan Department of Health and Human Services, in a state where cases have grown rapidly, continues to advise consumers to buy whole heads of lettuce rather than pre-washed, bagged or mixed salad kits. The department said interviews with more than 2,000 infected people found many did not report eating lettuce at a restaurant, though lettuce consumption was commonly reported in some setting.

Dr. Norman Beatty, an associate professor of medicine at the University of Florida College of Medicine, told CNBC the outbreak may still trace to one vendor, while the parasite’s characteristics could allow related smaller outbreaks to appear in other regions. He pointed to the outbreak’s spread across more than 30 states.

Food-service companies are also assessing reputational and demand effects. CNBC reported that Chopt, Panera Bread and Chipotle also saw traffic declines as concern over lettuce spread, according to Placer.ai data. Analysts cited by CNBC said they did not expect lasting financial damage for Taco Bell or other chains, though they said sales could be pressured temporarily and affected companies could face a one-to-two-quarter impact.

Yum Brands, Taco Bell’s parent company, has seen its shares fall nearly 9% over the past five days, according to CNBC. The National Restaurant Association said through CEO Michelle Korsmo that restaurants are required under the Food Code to have a food-safety-certified manager on each shift and that the group would support public health officials during the investigation.

This story draws on original reporting from CNBC.