What FDA Taylor Farms lettuce false positive means

The Food and Drug Administration’s reversal on a key piece of its cyclosporiasis investigation has sparked confusion in the U.S., but the agency said Monday that it has not changed its main conclusions about the outbreak.

The agency said Sunday a test that indicated a sample of iceberg lettuce supplied by Taylor Farms de Mexico carried the cyclospora parasite was a false positive. However, that only applies to one specific shipment of lettuce supplied by the company, which the agency does not believe was the vehicle that sickened more than 1,600 people and potentially thousands of others.

In a Monday clarification, the agency said its false positive does not change its prior conclusion that the outbreak is linked to shredded iceberg lettuce from central Mexico supplied by Taylor Farms, which was also served at some Taco Bell locations. The agency is still advising Americans not to eat recalled iceberg lettuce.

“FDA’s traceback investigation and outbreak data continue to converge on shredded iceberg lettuce from Taylor Farms locations in central Mexico,” it said in a statement. “FDA will continue to work with federal and state partners to investigate this multistate outbreak and ensure products implicated in this outbreak have been removed from the market.”

Investigators are continuing to examine what exactly caused the outbreak, which can lead to symptoms similar to a bad stomach bug for days or even weeks. CNBC has reached out to the FDA for details on the next phase of the investigation, including whether additional ingredients or suppliers are under scrutiny and whether the agency expects to issue further guidance. The agency has not yet responded.

The false positive test comes as the developing investigation creates uncertainty for both consumers and the food industry. While the FDA has said not to eat iceberg lettuce from Taylor Farms, some diners have stayed away from salads altogether as the number of cases rises.

“Unfortunately, this latest development may add further confusion to what has already been a complex situation for consumers,” said Frank Yiannas, former deputy commissioner of food policy and response at the FDA.

Though industry analysts do not expect the outbreak to have a long-term impact on Taco Bell or other restaurant chains, it could at least temporarily hit sales, based on foot traffic data, and cause a one-to-two quarter hit for companies linked to it. Foot traffic at Taco Bell sank roughly 19% on Friday compared to the day-of-the-week average so far this year, according to data from research firm Placer.ai.

In foodborne outbreak investigations, a false positive can happen when an initial screening signal isn’t reproduced during confirmation testing. Some doctors have pointed out that cyclospora is particularly challenging to recreate in the lab.

But it has not caused a shift in how public officials view the root of the outbreak.

The Department of Health and Human Services in Michigan, where the outbreak has seen explosive growth, says it continues to recommend that people purchase whole heads of lettuce rather than pre-washed, bagged or pre-mixed salad kits.

The agency added that based on interviews with more than 2,000 infected patients, many of them did not report eating lettuce at a restaurant, though they frequently said they ate the leafy green in some setting.

Taylor Farms said Monday morning it will continue its voluntary recall of implicated iceberg lettuce from central Mexico, and Taco Bell has already started to remove the suspected lettuce from restaurants in affected states.

The ripple effects go beyond those companies.

Walmart said Monday that it proactively removed four bagged salad kit products, which are under its Marketside brand and supplied by Taylor Farms, from stores across 27 states even though it said there was no indication that its products are part of the outbreak.

“There have been no confirmed illnesses associated with these products at this time,” the company said in a statement. “We are working closely with our supplier and took immediate steps to remove the products from sale.”

Former FDA Commissioner Dr. Scott Gottlieb suggested to CNBC that the test result does not clear Taylor Farms of its link to the outbreak. The Friday recall was for a product that was imported several weeks ago and was separate from the lettuce that tested positive with the FDA, he said.

He also noted that because cyclospora has an incubation period of up to two weeks and lettuce has a short shelf life, it is important to test multiple shipments, even if they originated from the same farm.

While the outbreak may be sourced to a single vendor for now, it’s possible the contamination has already spread wider, according to Dr. Norman Beatty, an associate professor of medicine at the University of Florida College of Medicine.

“We may find that this current outbreak may have led to additional outbreaks because of the nature of this parasite,” Beatty told CNBC. “The reason why this is important for this current outbreak is because there’s over 30 states where this has been isolated, and there could be other smaller outbreaks occurring in other regions.”

For restaurants, uncertainty is proving as challenging as the outbreak itself. Salad-focused chains and other operators that rely heavily on fresh produce are left without knowing whether any other ingredients are still a potential risk.

Taco Bell told CNBC in a Saturday statement that it had voluntarily removed all suspected lettuce from its locations within 72 hours of beginning the process and adjusted its supply chain accordingly. The company added that it is “confident” that consumers can eat safely at its locations.

“Clearly, this is a nationwide industry-wide issue, not a Taco Bell-specific issue,” the company said. “We hope that other members of the industry are taking the same degree of immediate action and accountability for the consumer as we have.”

Taco Bell isn’t the only restaurant seeing its business slow, according to Placer.ai. Other restaurant chains that sell lettuce, including Chopt, Panera Bread and Chipotle, also saw declines in traffic Friday, the firm said.

As headlines about the outbreak swirled last week, the industry’s top advocacy group stressed it is taking food safety seriously.

“The Food Code requires that every restaurant must have a manager that is food safety certified on every shift,” said National Restaurant Association CEO Michelle Korsmo in a post on LinkedIn.

“We’ll continue to support public health officials as they investigate the outbreak and ensure our members have the information they need to evaluate their food safety decisions,” she added.

And despite the false positive result, Taylor Farms and Taco Bell parent Yum Brands are still navigating the reputational fallout of an outbreak that prompted product removals and widespread headlines. Even so, restaurant analysts previously told CNBC they did not expect a long-term financial hit for the companies linked to the outbreak.

Shares of Yum Brands are down nearly 9% in the last five days.