Federal and state health officials are investigating whether Taco Bell restaurants may be connected to a multistate outbreak of cyclosporiasis, a gastrointestinal illness caused by a parasite that can contaminate fresh produce, The Washington Post reported.

More than 4,000 people, mostly in Michigan, have been sickened, with more than 80 hospitalizations reported.

Authorities have not identified a specific supplier or product responsible, but Michigan health officials say lettuce or salad greens are the leading suspected source based on interviews with more than 1,000 patients. Some Detroit-area Taco Bell locations recently stopped selling lettuce, cilantro onion, pico de gallo, and guacamole amid a reported nationwide recall.

Taco Bell has not publicly explained the decision or responded to requests for comment. Health officials say some patients reported eating at Taco Bell, though others did not, suggesting the outbreak may involve multiple sources.

Read more at The Washington Post.