FDA investigators found Cyclospora in two environmental samples collected in Mexico during their investigation of the massive summer outbreak.
The outbreak linked to Taylor Farms de Mexico iceberg lettuce ultimately sickened 12,883 people in 21 states, hospitalized at least 570 and was associated with two deaths.
The FDA says the findings strengthen the link to the lettuce, but investigators still have not determined exactly how the contamination occurred.
Federal health investigators have found Cyclospora at locations in Mexico connected to the record-setting outbreak that sickened nearly 13,000 people in the U.S. this summer.
The Food and Drug Administration (FDA) said Oct. 2 that testing detected the parasite in two environmental samples collected during inspections of Mexican lettuce growers and a processing facility identified through its traceback investigation.
One positive sample came from a tank holding outgoing wastewater at the Taylor Farms de Mexico processing facility. The other was collected from a drainage ditch at an iceberg lettuce farm identified during the investigation.
The findings are significant because they provide physical evidence that Cyclospora was present in the environment where lettuce associated with the outbreak was grown and processed.
However, the FDA stopped short of saying investigators have identified precisely how the lettuce became contaminated.
"While there is currently not enough evidence to conclusively determine how contamination occurred," the agency said, the environmental findings add to epidemiological and traceback evidence linking the outbreak to recalled shredded iceberg lettuce from Taylor Farms de Mexico.
Nearly 13,000 illnesses
The outbreak was one of the largest Cyclospora outbreaks recorded in the United States.
The final count reached 12,883 confirmed illnesses in 21 states, with at least 570 hospitalizations and two deaths. Illnesses began June 14 and continued through Aug. 17. The two deaths were reported in Michigan.
The actual number of infections was probably higher because some people recover without seeking medical care and are never tested, according to the Centers for Disease Control and Prevention (CDC). At the outbreak's peak, before the recall, more than 1,000 infections occurred in a single day.
Investigators eventually traced illnesses to processed iceberg lettuce supplied by Taylor Farms de Mexico. Some of the lettuce was served at Taco Bell restaurants, while other affected products were sold through retail and food-service channels.
Taylor Farms de Mexico recalled iceberg lettuce sourced from central Mexico on July 17. The FDA later classified the recall as Class I, its most serious recall category, because exposure could result in serious health consequences or death.
The CDC declared the outbreak over Sept. 11, and the FDA says the recalled lettuce is no longer on the market.
What investigators found in Mexico
Working with Mexican authorities, FDA investigators inspected several farms and a processing facility connected to the lettuce supply chain. Samples were taken from water, soil, sediment, and lettuce.
Two environmental samples came back positive for Cyclospora — the wastewater tank at the processing plant and the drainage ditch at a lettuce-growing operation.
The FDA said genetic analysis of the samples has been completed and investigators are continuing to compare the results with genetic information from clinical specimens collected from people who became sick.
That work could provide additional clues about how the parasite moved through the growing or processing environment.
Cyclospora cayetanensis is a microscopic parasite that causes cyclosporiasis, an intestinal illness. The most common symptom is prolonged or recurring watery diarrhea. Other symptoms can include loss of appetite, stomach cramps, bloating, nausea, and fatigue.
FDA plans changes before next growing season
Although the outbreak investigation has formally ended, the FDA says its work isn't finished.
The agency announced 10 actions it plans to take before the 2027 growing season, including increased surveillance of foods historically associated with Cyclospora, additional work with growers to reduce contamination risks, and an update to its Cyclospora prevention and response plan.
The FDA also plans to publish a report detailing its investigation and recommendations for preventing similar outbreaks.
For consumers, there is no continuing warning involving the lettuce from this outbreak. The products' use-by dates have passed, and federal health officials say the recalled lettuce is no longer being sold in stores or restaurants.