Michigan appears to be the epicenter of the outbreak, but so far more than 30 states have also reported infections in the last two weeks.

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

State and federal investigators are probing the fast-food chain’s possible connection to cyclosporiasis

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