Federal health officials have identified lettuce from Mexico served at Taco Bell locations across five U.S. states as a source of a widespread outbreak of diarrhea-causing parasite cyclospora.

“Early information has shown lettuce as a common product that regularly comes up during the investigation,” said the Michigan health department.

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.