The US Centers for Disease Prevention has been working to find the source of a parasitic illness that causes “explosive”, watery diarrhea, with more than 400 cases of the sickness reported across 18 states.

The parasite, cyclospora, spreads through raw produce and water contaminated with human feces – and it causes the intestinal illness cyclosporiasis, whose symptoms include cramps, nausea, fatigue, loss of appetite, low-grade fever and vomiting. The most commonly reported symptom is “watery diarrhea with frequent and sometimes explosive bowel movements”, according to the CDC.

There were 145 cases of cyclosporiasis reported across 17 states between 1 May and 16 June, the CDC said. Of those cases, 20 resulted in hospitalization.

Cyclosporiasis is not usually life-threatening, and no deaths amid the recent outbreak have been reported.

New York, Texas, Illinois and Michigan have been the hardest hit. Other states with reported cases include Alaska, Colorado, Connecticut, Florida, Georgia, Louisiana, Massachusetts, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia and Wisconsin.

Outside the dates of the CDC’s count, health officials in Michigan have been investigating an unusually high number of cases in a “large and growing outbreak”. More than 300 cases had been reported since 22 June as of Friday, in a state that typically only identifies about 50 cases of cyclosporiasis annually, according to its health department.

And since 1 May, New York has seen 107 cases. It typically records 500 to 700 cases statewide annually, according to the New York state health department. Health officials in New York City report that cases there roughly doubled from January through June compared to the same period in 2025, according to the New York Times.

The CDC said it is working with the US Food and Drug Administration (FDA) and local officials to investigate clusters of cases in several states. Those people became sick after eating food in the US and had not reported any travel in the fortnight before becoming ill.

There was no immediate evidence of a single, multi-state outbreak linking all cases, the CDC said. Investigators therefore were working to identify various potential clusters and sources of illness in multiple states.

In the US, the illness is seasonal, with cases usually peaking between May and August. During the spring and summer months, people typically eat a lot of fresh produce such as basil, cilantro, spinach and berries, which have been linked to past outbreaks.

The CDC said the latest cases were alarming for the moment due to the unusually high number and as of yet unidentified sources.

It can usually take anywhere from two days to two weeks to develop symptoms after ingesting the parasite, and not everybody experiences symptoms, the CDC said.

In more severe cases, the infection is typically treated with antibiotics. Most people with healthy immune systems, however, recover from cyclosporiasis on their own in days or weeks.

The CDC advises people to wash all fresh produce thoroughly before eating it – and to thoroughly wash hands and kitchen surfaces too. If people have symptoms of cyclosporiasis, they should see their healthcare provider, the CDC said – and if they test positive, they should report it to their local health department. Those who are ill should drink plenty of water and other fluids to avoid dehydration.

The disease is not typically transmitted from person to person.