The FDA has concluded its investigation into a nationwide Cyclospora outbreak, finding that recalled shredded iceberg lettuce from Taylor Farms de Mexico was strongly linked to nearly 20,000 confirmed illnesses.

The agency said Friday that investigators detected Cyclospora, the parasite responsible for the illnesses, in the environment where the recalled lettuce was grown and processed in Mexico. It could not determine the precise method of contamination, but two environmental samples tested positive. One came from a tank containing outgoing wastewater at Taylor Farms de Mexico’s processing facility. The other was collected from a drainage ditch at an iceberg lettuce farm identified through the FDA’s traceback investigation.

Patient illness reports and supply-chain tracking provided strong evidence connecting the recalled lettuce to the multistate outbreak. Genetic testing of the two positive environmental samples has been completed, and the FDA is continuing to compare those results with genetic testing from patient samples. Taylor Farms de Mexico did not immediately respond to a request for comment.

Cyclospora causes cyclosporiasis, an intestinal illness typically linked to contaminated food or water. The Centers for Disease Control and Prevention declared the outbreak over on Sept. 11. As of Sept. 14, the CDC had received reports of 19,883 laboratory-confirmed cases and two deaths.

The FDA also announced a 10-point plan aimed at preventing similar outbreaks ahead of the 2027 growing season. The plan includes increased monitoring of produce historically associated with Cyclospora outbreaks, additional outreach to growers, and an investigation report with recommendations for preventing future contamination. The measures are intended to strengthen prevention and detection efforts following the large multistate outbreak.