Mystery parasite leaves Americans battling ‘explosive diarrhea’ as CDC investigates

Federal health officials are attempting to track down the source of a microscopic parasite that triggers prolonged gastrointestinal illness, as domestic cases begin to climb for the summer season.

As of mid-June, the Centers for Disease Control and Prevention had confirmed 145 cases of cyclosporiasis across 17 states as of mid-June 2026, all linked to infections acquired in the U.S.

The culprit is Cyclospora, a microscopic parasite known to cause cyclosporiasis.

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The hallmark symptom of the infection is watery, often "explosive" diarrhea that can last for weeks or even months if left untreated, the CDC says.

Other symptoms include severe abdominal cramping, bloating, nausea, fatigue and significant weight loss.

The official outbreak season for the parasite runs from May 1 through Aug. 31, a window where warmer temperatures historically coincide with a spike in infections, according to the CDC.

Cases have cropped up in states ranging from Texas to Alaska. New York has been hit the hardest so far, reporting between 31 and 80 cases, followed by Texas and Illinois, which have each reported between 11 and 30 cases.

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While the infection can sometimes clear up on its own, it frequently requires antibiotics. Out of the 145 confirmed cases, 20 patients have required hospitalization, per the CDC.

No deaths have yet been reported. Patients range from 5 to 86 years old, though the median age is 42, and women make up 61% of the reported cases, data shows.

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The CDC, alongside the Food and Drug Administration and state health officials, is actively investigating several multi-state clusters, but they have yet to find a cause behind the spread.

"There is currently no evidence of a single, multistate Cyclospora outbreak linking all cases," the CDC noted in its surveillance report.

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The CDC advises anyone experiencing symptoms of cyclosporiasis to contact a healthcare provider for testing and treatment.