Public health officials are reportedly investigating if lettuce served at Taco Bell restaurants played a role in an outbreak of a gastrointestinal illness called cyclosporiasis that has sickened thousands of people across the country, the Washington Post reported Tuesday.

Citing two unnamed sources, the Post reported federal and state health officials are looking into the fast food chain after Detroit-area Taco Bell restaurants posted signs they were “currently unable to sell Lettuce, Cilantro Onion, Pico de Gallo, and Guacamole due to a nationwide recall.”

No specific produce grower or supplier has been identified as the source of the cyclosporiasis outbreak, and Taco Bell has not elaborated on the signs or why executives think their produce may be connected.

More people have been sickened in Michigan than any other state—including dozens of hospitalized patients—and health officials there on Monday said they believe the outbreak is linked to leafy lettuce.

Sources told the Post some of the sick patients did report eating at Taco Bell but others didn’t, which suggests the chain is not the sole source of the spreading foodborne pathogen.

Forbes has reached out to Taco Bell for comment.

Cyclosporiasis is an intestinal illness caused by a parasite called Cyclospora cayetanensis. It infects people who eat food or drink water infected with the parasite, and it can cause weeks of “explosive” bowel movements, according to the Centers for Disease Control and Prevention. Cyclosporiasis is typically not fatal or life-threatening, but some people with the infection are hospitalized for help managing symptoms. It can also be treated with combination antibiotics.

WHAT IS THE CURRENT CYCLOSPORIASIS SITUATION?

Thousands of people have been sickened across the country with cyclosporiasis in the last several weeks, and state and federal health agencies are working to investigate the source of the outbreaks. More than 2,6000 cases have been reported in Michigan, more than 500 in Ohio and nearly 400 cases in New York, mostly in New York City. Federal officials have warned cyclosporiasis cases are likely to be underreported because many people won’t seek professional medical help to recover. Officials can’t pinpoint the exact source or sources of this outbreak but it is linked to contaminated fresh produce, with the Michigan officials pointing specifically to lettuce and bagged salad greens.

33. That’s how many states had reported cyclosporiasis cases between May 1 and July 9, according to the CDC. The only states that had not been hit were Hawaii, Washington, Oregon, Idaho, Nevada, Arizona, New Mexico, Montana, Wyoming, North Dakota, South Dakota, Oklahoma, Missouri, Mississippi, Alabama, South Carolina, Delaware, Vermont and Maine.

HOW TO AVOID CYCLOSPORIASIS

Health departments say to run all fresh fruits, vegetables and herbs under clean, running water and scrub firm produce with a brush. Washing the produce won't kill the parasite, but may remove it. Heating or cooking produce to at least 158°F is the most effective way to kill the cyclosporiasis-causing parasite. Frozen vegetables are largely safe from cyclospora because more commercial facilities wash and blanch (briefly dip in boiling water) them before they're packaged, but some items (like raspberries) can’t be blanched ahead of freezing. Canned produce is considered the lowest-risk option during a cyclosporiasis outbreak because commercial canning relies on high heat to seal food.