US declares end to record cyclospora outbreak as source remains unclear

US health officials have declared an end to the largest cyclospora outbreak in the country's history, even as the precise origin of the contamination remains unexplained.

The Food and Drug Administration said it is confident that all recalled iceberg lettuce linked to the outbreak has been removed from the market. The agency has also concluded on-site inspections and sample collection at iceberg lettuce growers and a processing facility in Mexico, with results from those samples still pending analysis.

Nearly 13,000 reported cyclospora cases were connected to the multistate outbreak, accounting for the bulk of an unprecedented national surge in the parasitic illness this year. Since May 1, authorities have received reports of almost 20,000 laboratory-confirmed cases — more than 16 times the number recorded over the same period last year. A further 6,100-plus suspected cases have also been reported. The worst previous year on record was 2019, when about 4,700 infections were reported nationwide.

The 2025 surge was dominated by an outbreak spanning 21 states and linked to iceberg lettuce, though thousands of other cases have not been tied to that cluster. Michigan recorded the most cases and the two deaths associated with the outbreak.

Investigators initially focused on lettuce served at Taco Bell before turning to Taylor Farms as the source. The company recalled iceberg lettuce grown in central Mexico, along with thousands of packaged salad products that combined the lettuce with other vegetables. Those products had been shipped to major US restaurant chains, including Yum Brands, which owns Taco Bell, Pizza Hut and KFC.

Cyclospora is a microscopic, spherical parasite that typically causes watery diarrhoea, sometimes with frequent and explosive bowel movements, according to the Centers for Disease Control and Prevention. Outbreaks tend to cluster in late spring and summer. The resulting illness, cyclosporiasis, is less common than foodborne infections caused by salmonella or E. coli, and many cases are never linked to a specific food or source.

The parasite spreads through human faeces, and it is still unclear how sewage could have contaminated enough produce to sicken so many people. Ellen Shumaker, director of outreach for the Safe Plates food safety programme at North Carolina State University, noted that such contamination can occur when produce is grown in soil or comes into contact with contaminated water.

The outbreak has drawn attention to a broader concern: US regulators are conducting fewer international inspections to catch contaminated produce before it reaches American consumers.