The Food and Drug Administration is investigating iceberg lettuce supplied to Taco Bells by Taylor Farms as a possible source in an escalating outbreak of cyclosporiasis in four Midwestern states, a stomach bug that causes weeks of severe diarrhea, according to a person familiar with the investigation.

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Nationwide, nearly 7,000 people nationwide may have been sickened, with 1,645 of those cases confirmed and more than 5,100 still under investigation, according to the Centers for Disease Control and Prevention. No deaths have been reported.

Earlier this week, the CDC announced an investigation into more than 400 cases in Michigan, Ohio, West Virginia and Kentucky.

The possible outbreak source was first reported by the Washington Post.

Taylor Farms and Yum Brands, the parent company of Taco Bell, did not immediately respond to requests for comment.

The Midwest outbreak is unlikely to account for all cases across the country. Experts said there could be multiple outbreaks from different sources.

Michigan has been hit hardest this summer, with 4,312 cases as of Thursday. (The CDC’s counts often lag behind state counts.) The state’s health department said that 102 people in Michigan have had to be hospitalized.

Michigan health officials previously flagged lettuce and salad greens as a potential source based on more than 1,000 interviews with people who’ve tested positive.

Getting to the source of the outbreak has been difficult, as the incubation period for the parasite to make a person sick can be up to two weeks.

A spokesperson for Taco Bell said Tuesday it had “voluntarily and temporarily removed limited ingredients” at some of its restaurants as a precaution, adding that “public health officials have not confirmed a link to Taco Bell or any specific ingredient, supplier, restaurant or retailer.”

This isn’t the first time Taylor Farms has been connected to a cyclosporiasis outbreak. In 2013, 631 people in 25 states were sickened by a salad mix linked to the company, health officials concluded. Many of the illnesses occurred in Iowa and Nebraska among people who’d eaten at Olive Garden and Red Lobster. The outbreak was eventually traced to a salad mix from a Taylor Farms processing plant in Mexico.

Health officials also determined that Taylor Farms was also at the root of a 2024 E. coli outbreak linked to slivered onions on McDonald’s Quarter Pounder hamburgers. According to the FDA, 104 people were sickened in 14 states in that outbreak. Nearly three dozen were hospitalized, four people, including at least one child, developed severe kidney problems. One person, an older adult from Colorado, died.