CDC investigates parasite that’s caused cases of ‘explosive’ diarrhea in 18 US states

The US Centers for Disease Control and Prevention is actively investigating a parasitic illness that has caused more than 400 cases of severe, watery diarrhea across 18 states. The culprit, a parasite called Cyclospora, typically spreads through raw produce or water contaminated with human feces, leading to an intestinal illness known as cyclosporiasis.

Symptoms of cyclosporiasis include cramps, nausea, fatigue, loss of appetite, low-grade fever, and vomiting. However, the most commonly reported and defining symptom is “watery diarrhea with frequent and sometimes explosive bowel movements.” Between May 1 and June 16, the CDC recorded 145 cases across 17 states, with 20 individuals requiring hospitalization. While the illness is not usually life-threatening and no deaths have been reported in this outbreak, the sheer number of cases is concerning.

Michigan and New York are particularly hard-hit. Michigan health officials are investigating a large and growing outbreak, with over 300 cases reported since June 22, a significant surge compared to the state's typical annual total of about 50 cases. New York has seen 107 cases since May 1, and health officials in New York City note that cases have roughly doubled from January through June compared to the same period in 2025.

The CDC, in collaboration with the US Food and Drug Administration and local authorities, is working to identify potential clusters and sources of illness. While the illness is seasonal in the US, typically peaking between May and August, the current outbreak is alarming due to its high numbers and as-yet unidentified sources. The parasite's incubation period can range from two days to two weeks, and not everyone infected develops symptoms. Treatment usually involves antibiotics for more severe cases, though many with healthy immune systems recover on their own.

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watery diarrhea with frequent and sometimes explosive bowel movements