The largest-ever outbreak of cyclosporiasis in the U.S. has ended, the Centers for Disease Control and Prevention said Friday.

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The foodborne illness sickened 12,833 people in 21 states in recent months in the largest cluster, the CDC said. Health officials have linked that outbreak to shredded iceberg lettuce supplied by Taylor Farms in Mexico.

It fueled the worst cyclosporiasis season in U.S. history, with 19,595 overall cases of the illness caused by the parasite cyclospora. The U.S. recorded two deaths, both in Michigan, the epicenter of the biggest outbreak.

The foodborne illness spread sparked scrutiny of U.S. food safety procedures and corporate consolidation in the country’s food supply, along with staffing and funding at the U.S. Food and Drug Administration.

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The outbreak also led to lower sales at restaurants that offer fresh lettuce — particularly Taco Bell, which served shredded iceberg lettuce from Taylor Farms — and dampened lettuce sales at grocery stores.

Cyclospora was challenging for health officials to track because of its long incubation period. It can take weeks to trace back the source of the illness, after which implicated produce may have spoiled.

Taylor Farms recalled the iceberg lettuce, including packages sold in grocers such as Walmart, in July. Taco Bell also pulled the lettuce from its restaurants that month.

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