The US Food and Drug Administration has withdrawn a laboratory finding that appeared to confirm Cyclospora contamination in shredded iceberg lettuce from Taylor Farms de Mexico, declaring it a false positive after a secondary review. The retraction, announced on 19 July, does not alter the agency’s traceback investigation or the voluntary recall of the product, which remains in effect. More than 1,600 confirmed cases of cyclosporiasis have been recorded across 34 states since May, with at least 94 hospitalisations, and the epidemiological evidence continues to converge on lettuce supplied to Taco Bell restaurants in five Midwestern states.

Viewed from Washington, the episode exposes the diagnostic difficulty of pinning down a parasite that cannot be cultured through standard enrichment techniques. The initial polymerase chain reaction test, conducted on a sample collected at the southern border, produced a signal that FDA experts later judged to be an artefact rather than true amplification. The agency stressed that the false positive does not weaken the “overwhelming epidemiological data” linking the outbreak to Taylor Farms’ central Mexican operations. The company, which said the FDA apologised for the error, is maintaining its recall of iceberg lettuce grown and processed in that region, while emphasising that no retail-branded salad products are affected.

Mexican health authorities have pushed back against any suggestion that the outbreak originated on their soil. Health Secretary David Kershenobich told a presidential press conference that only three domestically acquired cases have been detected in Mexico, all within normal seasonal levels, and that the country is not experiencing an outbreak. A Mexican inspection team has been dispatched to the Guanajuato facility to collect samples and conduct its own investigation in coordination with the US Centers for Disease Control and Prevention. So far, Kershenobich said, no evidence has been found to implicate the site.

Beyond North America, the outbreak is drawing attention to gaps in parasite surveillance. Australian parasitologists note that Cyclospora is not a notifiable disease in their country and that routine diagnostic panels often overlook it, raising the risk of delayed detection should the pathogen arrive via imported produce or infected travellers. The US response has itself been questioned after cuts to the Foodborne Diseases Active Surveillance Network, though Health and Human Services Secretary Robert F. Kennedy Jr. described the reductions as targeting redundant systems and insisted the outbreak is “under control.”

The next factual milestone will be the results of Mexico’s independent sampling, expected in the coming days, alongside any further laboratory-confirmed product matches from the FDA’s ongoing collection of samples from the implicated supply chain.