The number of people who have gotten sick and the geographic spread of cases points to more than one source

Michigan has said contaminated lettuce may be to blame for the cyclospora outbreak in the state.

It's possible that the cyclosporiasis sickening people across the U.S. has more than one source.

Michigan is the center of the outbreak of a gastrointestinal illness caused by a parasite called Cyclospora cayetanensis. The state's health officials said this week that lettuce may be the cause of epidemiologically linked infections in Kentucky, Michigan, Ohio and West Virginia.

At the same time, CNN has reported that the Centers for Disease Control and Prevention is investigating cucumbers, cilantro, and white and green onions to see if they are responsible for cyclosporiasis cases in four other states: Illinois, New York, Pennsylvania, and Texas.

"This outbreak is very unique," said Kalmia Kniel, professor of microbial food safety at the University of Delaware. "The way the numbers are growing and the way we have geographical clustering, there's probably many outbreaks."

The infections could be caused by different kinds of contaminated produce grown on the same farm, produce that was contaminated during the distribution process or even contaminated water. It could also mean that these are distinct outbreaks. Back in 2018, there was an outbreak of cyclospora that was caused by two different contaminated produce products: a McDonald's $(MCD)$ salad mix that sickened 501 people, and a Del Monte $(DMC)$ vegetable tray that made 248 people ill.

"It's what we call a multi-focal outbreak," said Amy Edwards, associate medical director for infection control at University Hospitals in Ohio. "When it's a single item like parsley, it might be a bit easier to trace. If two or three different types of items are making people sick, that can be a lot harder to pin that down."

Cyclospora is seasonal, with outbreaks usually occurring in the spring and summer due to contaminated seasonal produce like raspberries, basil and salad greens. It can take several weeks to formally diagnose cyclosporiasis because symptoms may not appear for at least to two weeks. And when patients present with unexplained watery diarrhea or other symptoms like abdominal cramping, testing for cyclosporiasis is not part of routine care. In some cases, patients have to supply multiple stool samples before cyclospora is detected.

"It usually is a diagnosis that's made later," Edwards said, "when things aren't going well, because they're just not getting better and a deeper investigation is done."

Cyclospora outbreaks happen every year, but this one appears to be the largest on record. There are 6,745 confirmed and suspected cases, as of July 14, according to the CDC. At this time last year, there were 249 cases. About 2,600 of this year's infections are in Michigan, which normally gets about 50 cases of cyclosporiasis a year.

The most recent large outbreak was in 2019, when there were 2,408 cyclosporiasis infections from contaminated basil.

Health officials still don't know the cause of this outbreak, which has affected people in 34 states, and the CDC said this week that the outbreak may not be resolved until August.

"What makes this one a little different is that we still haven't figured out, or the CDC hasn't been able to pinpoint, where it's coming from," said Kaitlin Pander, a food-safety and quality educator at Penn State Extension.

Some experts have questioned whether the reductions in staffing at the CDC under the Trump administration have contributed to the delays in identifying the source of the outbreak.

Joel Barratt, an associate professor of pathology and laboratory medicine at Emory University, said he left the CDC last year when the cyclospora outbreak-response team that he led was cut from 11 staffers to three. That team handled the genetic testing of cyclospora cases and coordinated getting samples to the CDC. The CDC did not respond to a request for comment about the cuts.

"I would expect these small- and medium-scale outbreaks to become more frequent and to get more out of control if we don't get a handle on this and fully staff and fully fund the CDC," along with local and state health departments, Edwards said. "This sort of stuff just doesn't need to happen."

-Jaimy Lee

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July 15, 2026 17:27 ET (21:27 GMT)

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