FDA inspectors found the cyclospora parasite at a farm in Guanajuato, Mexico, linked to a U.S. lettuce outbreak with nearly 13,000 reported cases. The agency has not determined how the contamination occurred.

Inspectors detected the parasite in a wastewater tank and a drainage ditch used for lettuce cultivation. The FDA said the findings strengthen the link between the outbreak and the Taylor Farms site. Taylor Farms attributed the contamination identified by the agency to an independent grower that is no longer in its supplier program, and said its central Mexico facility remains closed while it works on stronger safety measures.

U.S. officials declared the outbreak over last month. The FDA said it is confident that all iceberg lettuce recalled in connection with this outbreak is off the market. Cyclospora can cause watery diarrhea.