FDA Closes Its Lettuce Outbreak Case Without Saying How the Parasite Got In

The Food and Drug Administration closed its outbreak investigation into recalled iceberg lettuce on Oct. 2 and reported that two of the samples it collected in Mexico tested positive for Cyclospora, the parasite behind the illnesses. One came from a tank holding outgoing wastewater at the Taylor Farms de Mexico processing plant. The other came from a drainage ditch at an iceberg lettuce grower the agency had traced the recalled lettuce back to.

The agency says the positive samples show the parasite was present in the environment where the lettuce was grown and processed, and that they add to the case data and product tracing already linking the outbreak to the recalled shredded lettuce. It also says there is still not enough evidence to determine conclusively how the lettuce became contaminated.

The FDA's sampling in Mexico covered water, soil, sediment and lettuce. Neither of the positives came from lettuce. Earlier in the outbreak the FDA reported a positive lettuce sample taken at the border and then withdrew it; its laboratory experts had re-reviewed the result and concluded it was a false positive.

Genotyping of both positive samples, a comparison of their DNA, has been completed, and the agency is still working out how those results relate to the DNA taken from people who got sick.

The outbreak was traced to shredded iceberg lettuce from Taylor Farms de Mexico, which voluntarily removed all iceberg lettuce sourced from central Mexico from the U.S. market on July 17. The CDC declared the outbreak over on Sept. 11, with 12,883 illnesses counted.

The FDA says its post-outbreak work continues, and it is posting the Cyclospora prevention activities it plans before the 2027 growing season.