FDA false positive adds twist to Taylor Farms lettuce outbreak probe
Taylor Farms says the FDA apologized after a cyclospora test was ruled false positive, while regulators keep investigating iceberg lettuce.
By Frankie Delgado · News Reporter
3 min read
A cyclospora test that appeared to tie Taylor Farms iceberg lettuce to a multistate outbreak has been ruled a false positive, according to the Food and Drug Administration, adding a fresh complication to a fast-moving food-safety investigation.
Taylor Farms said in a statement that the FDA “apologized to us” after the agency said over the weekend that the earlier result did not confirm contamination in the lettuce sample.
The FDA and the Centers for Disease Control and Prevention are still investigating iceberg lettuce sold by Taylor Farms as they work to confirm the source of the outbreak. Regulators have linked the outbreak to cyclosporiasis, a gastrointestinal infection caused by the parasite Cyclospora cayetanensis.
According to regulators, at least 1,600 people have been sickened with severe gastrointestinal symptoms including watery diarrhea and abdominal cramping. As of July 15, 1,644 people had tested positive, while about 6,700 people were believed to have cyclosporiasis.
Why one test changed the picture
Kalmia Kniel, a professor of microbial food safety at the University of Delaware, said by email that the latest turn was unusual, while also fitting for a difficult outbreak.
“Cyclospora is one of the most notoriously difficult pathogens to detect in agricultural matrices,” Kniel said.
Kniel said several things could explain a false positive, including detection of a closely related organism, too few oocysts on lettuce leaves to support a firm result, a sequencing failure, or the difficulty of testing leafy greens for the parasite. Leafy greens can produce background “noise” that makes a positive result harder to determine, she said.
Food-safety experts said the false positive does not automatically clear Taylor Farms lettuce as a possible source. Kniel said investigators often depend on epidemiological evidence because by the time a product is suspected, much of it has already been eaten and is no longer available for testing.
Recall remains in focus
Late last week, Taylor Farms said it would recall iceberg lettuce grown and processed at a farm in Guanajuato, in central Mexico.
In a Sunday statement, the company said, “At this moment, FDA has not identified a single positive product test result for Cyclospora.”
Taylor Farms is a privately held produce supplier based in Salinas, California, and operates in several countries. Its produce and salad kits are sold through national chains including Costco, Trader Joe’s and Amazon’s Whole Foods, and to restaurants including Chipotle. A Taylor Farms recall also covers the Marketside brand at Walmart.
The outbreak has been concentrated in five states and has affected people who ate at Taco Bell restaurants, according to regulators. Taco Bell is owned by Yum Brands.
The FDA has posted information on the outbreak investigation on its website and continues to work with the CDC as officials try to pin down the source. For consumers, the latest update means the investigation is still unresolved, even after a test result once seen as a key clue was withdrawn.
This story draws on original reporting from MarketWatch.