WASHINGTON — Federal health officials on Friday said they have linked cases of a diarrhea-causing parasite tied to shredded lettuce to an additional four states, expanding the scope of the largest U.S. outbreak of cyclospora.

The Centers for Disease Control and Prevention said the outbreak first tied to Taco Bell restaurants now includes Illinois, Kansas, Oklahoma and Pennsylvania. Previously the agency’s investigation included five states: Indiana, Kentucky, Michigan, Ohio and West Virginia.

The Illinois Department of Public Health said in an email Friday afternoon that it is “intensifying its investigation” as the agency continues to work with local, state and federal partners to determine all possible sources of the outbreak. A number of people reporting cyclosporiasis symptoms in Illinois had consumed shredded lettuce while dining out, IDPH said.

“July case reports are rising at a level we have not seen since 2018,” said Dr. Sameer Vohra, director of the IDPH, in a statement. “We recommend Illinois residents, but especially our elderly, infants and those with weaker immune systems, reach out to their health care provider if they experience sudden, ongoing diarrhea.”

As of Wednesday, Illinois had 508 confirmed or probable cases of cyclosporiasis. Of those, 156 individuals reported travel outside the U.S. and 291 acquired the illness domestically. The remaining cases are under investigation with unknown travel status, according to IDHP. So far, 39 people in Illinois have been hospitalized for treatment.

Vohra noted a few measures that could help prevent cyclosporiasis, including washing hands before preparing or eating food, thoroughly washing produce and, when appropriate, cooking produce to a temperature of at least 158 degrees.

IDPH said products that are suspected of being part of the outbreak are now being removed from restaurants, retail stores and other food service locations, and the agency “is hopeful that those actions and increased public awareness will lead to fewer cases in the days ahead.”

Cyclospora is more challenging than other parasitic illnesses to track down, Emily Landon, UChicago Medicine’s executive medical director of infection prevention and control, told the Tribune last week. The cyclosporiasis incubation period is two to 14 days, longer than that for other diarrheal illnesses, which makes it difficult to nail down a culprit, she said.

The CDC, Food and Drug Administration and state health officials have been tracing the supply of the lettuce and interviewing people across the nation about the foods they ate two weeks before getting sick.

The number of cases nationwide linked to lettuce served at Taco Bell is now 1,947, including at least 98 people who had to be hospitalized. There have been no deaths, the agency reported on its website.

The total number of people sickened by the outbreak is likely higher than the official tally, given that not all cases are reported, the agency noted.

FDA officials earlier this week said they remain focused on lettuce from Taylor Farms as the source of the multistate outbreak. The company last week announced it was recalling iceberg lettuce grown in central Mexico.

On Thursday, the FDA announced it was investigating a separate outbreak of cyclospora reported in 72 people. Regulators had not yet identified the products linked to the illnesses.

Overall, cyclospora cases have set a U.S. record. Since May 1, CDC has received reports of more than 4,100 laboratory-confirmed cases and is investigating more than 7,400 other likely cases across 41 states. Federal health officials have said that other “brands, restaurants, retailers, or distribution channels” could be tied to the outbreak as the investigation continues.

Cyclospora is a microscopic parasite that infects food that has come into contact with human feces, most commonly when produce is irrigated or washed with contaminated water. When ingested, the parasite causes intestinal illness marked by “frequent and sometimes explosive bowel movements,” according to the CDC.

On Thursday, Mexico health officials announced that the parasite was not detected in the lettuce or water at the Taylor Farms plant in the Mexican state of Guanajuato.

The results were announced following a visit by Mexican health authorities to the Taylor Farms plant between July 18 and 20, during which 10 samples of iceberg lettuce were collected. Four water samples also were collected for analysis, authorities stated.

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Syed reported from Chicago. Fabiola Sanchez contributed from Mexico City.

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