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

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

Nearly 7,000 cases of cyclosporiasis have been reported across the country

Upwards of 1,600 people who contracted cyclosporiasis reported eating at the chain beforehand, the CDC and FDA said.