The Food and Drug Administration (FDA) said Friday that it concluded its investigation into the Cyclospora outbreak associated with iceberg lettuce from Mexico, finding "strong" evidence linking the infections to recalled products from Taylor Farms de Mexico.

The cyclosporiasis outbreak — one of the largest foodborne illness events in recent U.S. history — has been linked to more than 12,800 cases across 21 states and hundreds of hospitalizations.

Two related deaths have been reported in Michigan, and both people had significant underlying health conditions, according to health officials.

The outbreak prompted a massive recall by Taylor Farms de Mexico, which announced in July that it was voluntarily pulling all iceberg lettuce sourced from central Mexico from U.S. shelves.

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Following the recall, the FDA initiated onsite inspections in Mexico.

During its traceback investigation, the FDA said it identified multiple farms and a processing facility in Mexico that supplied the recalled shredded lettuce distributed by Taylor Fresh Foods.

Two environmental samples tested positive for Cyclospora, according to the FDA.

The agency said one positive sample came from a tank that held outgoing wastewater from the company's processing facility. The other was taken from a drainage ditch at an iceberg lettuce farm.

Although the FDA said it was unable to determine how the contamination transpired, the agency said the data strongly suggested that the outbreak was tied to lettuce from Taylor Farms de Mexico.

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"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 said.

"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 agency added.

A spokesperson for parent company Taylor Fresh Foods addressed the FDA's findings in a statement to Reuters.

"The independent grower where a positive sample was found is no longer part of our supplier program. The sample FDA referenced came from discharged waste and sewer water outside of our processing facility," the spokesperson said.

"As FDA noted in its report, there is currently not enough evidence to conclusively determine how contamination occurred or how results for these samples relate to ongoing genotyping of clinical specimens," the spokesperson continued.

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FOX Business has reached out to Taylor Farms for comment.

The FDA said it is confident that all recalled iceberg lettuce linked to the outbreak is out of the U.S. market.

The Centers for Disease Control and Prevention (CDC) previously declared the outbreak over on Sept. 11.

Cyclospora is a single-celled parasite that can cause stomach cramps, nausea, fatigue, weight loss and other health problems, though some infected people remain asymptomatic, according to the CDC.