Health officials have identified shredded iceberg lettuce served at Taco Bell locations in five states as the source of the cyclosporiasis outbreak that has sickened thousands of people, the CDC confirmed Friday. The agency said an investigation conducted by the FDA tracked the affected lettuce to a single supplier in Mexico.

The cyclosporiasis outbreak has sickened thousands of people nationwide, and Michigan has been the hardest hit.

Michigan, which is where much of the outbreak is centered, has reported over 4,300 cases of cyclosporiasis, which can cause diarrhea and a low grade fever.