The Food and Drug Administration (FDA) said on Friday it has found a potential source of the cyclosporiasis outbreak that was tied to lettuce over the summer.

The agency collected samples during its onsite inspections of Taylor Farms de Mexico facilities, it said.

Two samples tested positive for the parasite, Cyclospora, according to the FDA. One positive sample was from a tank that held outgoing wastewater from a processing facility, the agency said. The second positive sample was from a drainage ditch of an iceberg lettuce grower, it noted.

“While there is currently not enough evidence to conclusively determine how contamination occurred in this outbreak, the positive samples show that Cyclospora was present in the environment where lettuce was grown and processed,” the FDA wrote in an update on its website.

“This adds to the strong epidemiological data and traceback convergence supporting the link between this outbreak and recalled shredded iceberg lettuce from Taylor Farms de Mexico,” the update continued.

The FDA said its investigation has closed. Health officials say they are confident that all recalled lettuce associated with this outbreak is off the market.  

At least 12,883 people were infected with cyclosporiasis across 21 states after eating the recalled lettuce, according to the Centers for Disease Control and Prevention (CDC). Thousands more cases were reported but health officials noted difficulties in tying infections to the recalled foods.

A total of 570 people were hospitalized and two people in Michigan died.  

In mid-July, the FDA and the CDC announced they were investigating a multi-state outbreak of cyclosporiasis illnesses linked to shredded iceberg lettuce served at some Taco Bell restaurants.

The lettuce was supplied to Taco Bell by Taylor Farms and sourced from central Mexico.

Taylor Farms de Mexico issued a voluntary recall of all iceberg lettuce sourced from central Mexico, with the recall affecting 27 states. The recalled products were distributed from June 29 through July 16 and have best-if-used-by dates up to Aug. 3.

Taco Bell said it is no longer using lettuce from Taylor Farms de Mexico at any of its restaurants.