FDA Retracts Cyclospora Test as Outbreak Source Remains Unknown

The U.S. Food and Drug Administration acknowledged Sunday that a laboratory result it had publicly reported the previous day — identifying cyclospora contamination in shredded iceberg lettuce produced by a Taylor Farms subsidiary in Mexico — was a false positive, leaving federal investigators without a confirmed source for an outbreak that has now sickened more than 1,600 people across multiple states.

The retraction came after FDA laboratory experts re-examined results from a sample collected at Taylor Farms de Mexico, concluding, in the agency’s own words, that “the finding does not represent true amplification and should be considered a false positive.” The erroneous result, generated by a rapid screening test, had been posted to the FDA’s website on Saturday before being quietly removed the following day. As of July 19, 2026, the agency confirmed that no product testing has returned a verified positive result for Cyclospora cayetanensis.

Despite the embarrassment, FDA acting food chief Donald Prater told reporters Monday that the agency’s epidemiological and traceback work continues to point toward shredded iceberg lettuce originating from Taylor Farms’ facilities in central Mexico. “FDA’s traceback investigation and the outbreak data continue to converge on shredded iceberg lettuce from Taylor Farms’ locations in central Mexico,” Prater said, offering no timeline for when laboratory confirmation might follow. The agency said it felt obligated to disclose the initial finding to the public but that a subsequent quality-control review exposed the error.

Taylor Farms stated that the FDA had apologised to the company, and stressed that no confirmed positive product test result has been established. The company’s voluntary recall of all iceberg lettuce grown and processed in central Mexico, initiated on July 17, remains in effect regardless. Taylor Farms also announced Monday that it has ceased sourcing iceberg lettuce from central Mexico for the remainder of the growing season — a decision that does not, on its own, resolve the question of how the parasite entered the supply chain in the first place.

Scale of the Outbreak and Supply Chain Response

The Centers for Disease Control and Prevention has linked the illness to Taco Bell restaurants in Indiana, Kentucky, Michigan, Ohio and West Virginia. As of Saturday, the CDC had recorded 1,644 confirmed cases and 94 hospitalisations, with no deaths reported. Suspected cases are believed to number in the thousands, though the precise figure remains unquantified by authorities.

Sysco, the largest food distributor in the United States, has halted distribution of Taylor Farms iceberg lettuce sourced from Mexico and instructed its customers to destroy any affected stock and prevent it from re-entering the food supply. Taylor Farms supplies lettuce to Taco Bell and a range of major grocery retailers, a distribution footprint that amplifies both the public health risk and the difficulty of containment.

Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis, transmitted through contaminated food or water. It is not typically spread directly between individuals, as the parasite requires days to weeks in the environment before becoming infectious. Symptoms — including frequent watery diarrhoea, nausea, fatigue, cramping and low-grade fever — generally appear approximately one week after exposure, and outbreaks cluster in late spring and summer.

The FDA says it is continuing to test lettuce samples and has expanded screening to produce crossing the southern border, though none of these tests have returned positive results to date. The gap between strong epidemiological suspicion and absent laboratory confirmation is, at this stage, the defining feature of an investigation that federal agencies have yet to resolve.