Detecting cyclospora is 'notoriously difficult.' Here's what the FDA's apology to Taylor Farms means.

By Jaimy Lee

The FDA and CDC are investigating iceberg lettuce sold by Taylor Farms to confirm the source of the outbreak of the gastrointestinal infection cyclosporiasis

Regulators said late last week that iceberg lettuce sold by Taylor Farms, based in Salinas, Calif., was linked to the cyclospora outbreak.

The cyclospora outbreak has taken another turn.

Over the weekend, the Food and Drug Administration said a test that confirmed that iceberg lettuce sold by Taylor Farms was contaminated with cyclospora had been a false-positive, raising even more questions for Americans about what is safe to eat right now. Taylor Farms said in a statement that the FDA "apologized to us."

The regulators are investigating a multistate outbreak of cyclospora, a parasite that is responsible for making at least 1,600 people sick with a severe gastrointestinal illness that causes watery diarrhea and abdominal cramping.

For people in the U.S. trying to figure out how to safely eat lettuce amid the outbreak, this is yet another layer to a complex story. Food experts, however, say that false-positives can occur when testing for Cyclospora cayetanensis, because of the complexity of the parasite.

"This is a bit unusual, fitting for this outbreak perhaps," said Kalmia Kniel, professor of microbial food safety at the University of Delaware, by email. "Cyclospora is one of the most notoriously difficult pathogens to detect in agricultural matrices."

She cited several reasons that this can happen: the test instead detected a closely related organism; there weren't enough of the pathogen's oocysts on the lettuce leaves to produce a solid result; the sequencing failed; or that leafy greens are difficult to test for cyclospora. "There is a background level of noise that makes it difficult to determine a positive," she said.

The outbreak has captured the attention of the American public. It is the largest cyclospora outbreak that has ever occurred in the U.S.; about 6,700 people are thought to have cyclosporiasis, and 1,644 have tested positive, as of July 15. The outbreak is heavily concentrated in five states, affecting people who ate at a Taco Bell restaurant. Yum Brands (YUM) owns Taco Bell.

And now that people in the U.S. know that the FDA and the Centers for Disease Control and Prevention are investigating Taylor Farms as the source of the outbreak, that has created more worry. The privately held produce supplier is based in Salinas, Calif., and operates in several countries. Its produce and salad kits are sold to national chains like Costco (COST), Trader Joe's and Amazon's (AMZN) Whole Foods, as well as in restaurants like Chipotle (CMG). A Taylor Farms recall also includes the Marketside brand at Walmart (WMT).

Late last week, Taylor Farms said it would recall iceberg lettuce grown and processed at a farm in Guanajuato, in central Mexico. "At this moment, FDA has not identified a single positive product test result for Cyclospora," Taylor Farms said Sunday in a statement.

The FDA is still telling Americans not to eat the iceberg lettuce recalled by Taylor Farms de Mexico as its investigation continues. "To clarify, this false-positive lab sample DOES NOT change the basis for FDA's ongoing outbreak investigation or the overwhelming epidemiological data supporting the current voluntary recall by Taylor Farms," the regulator wrote Monday on X.

Experts observed that Taylor Farms lettuce could still be the cause of the outbreak.

"Most often, we rely on good epidemiological evidence to support that a product is linked to an outbreak," Kniel said. "Detection is really difficult, and most often the produce item being implicated has been consumed, and there is nothing left to test."

-Jaimy Lee

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07-20-26 1441ET