Shredded iceberg lettuce supplied by Taylor Farms and sold at some Taco Bell restaurants has been linked to a multistate outbreak of cyclosporiasis, a source familiar with the investigation said Thursday.

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.

Nearly 7,000 cases nationwide are confirmed or under investigation, according to the CDC. Michigan has accounted for the bulk of cases so far.