A Parasite Outbreak Explodes Past 4,000 Cases Across 31 States — and the Source Is Still a Mystery

A fast-spreading outbreak of cyclosporiasis, a parasitic infection that causes explosive, prolonged diarrhea, has surged past 4,000 reported cases across at least 31 states, according to a tally compiled from state health departments — and investigators still have not pinned down the contaminated food driving it.

The scale is already extraordinary. The United States reported roughly 2,700 cyclosporiasis cases in all of 2025; the 2026 outbreak has blown past that figure with the summer far from over. As of July 9, the Centers for Disease Control and Prevention counted 843 domestically acquired cases, but the number tracked by state agencies has climbed far higher and faster in the days since, with health officials warning the true toll is likely higher still because many infections go undiagnosed.

Michigan has been hit hardest. The state's Department of Health and Human Services reported more than 1,250 cases tied to the outbreak investigation period and a running total that topped 2,600, prompting some businesses to pull menu items as a precaution — a bakery in Owosso removed products made with raw green onions even before any specific source was confirmed. New York, Ohio, Illinois and North Carolina round out the states reporting the sharpest rises.

Cyclospora is a microscopic parasite spread when people consume food or water contaminated with feces. It cannot be passed directly from person to person. Symptoms typically begin about a week after exposure and can be brutal and drawn out: watery diarrhea, cramping, bloating, nausea, fatigue and weight loss that can persist for weeks or even months if untreated. The infection is treated with antibiotics, but relapses are common.

What makes this outbreak so vexing is that no single culprit has been identified. In past years, cyclosporiasis has been traced to fresh produce including bagged salad greens, raspberries, basil, cilantro, green onions and snow peas — items that are eaten raw and hard to fully sanitize. This year, the Food and Drug Administration is investigating several clusters involving not-yet-identified foods, and Michigan officials say their source remains unknown.

Public health experts have also criticized gaps in tracking. Cyclospora surveillance is uneven from state to state, and reporting lags have made it difficult to see the full national picture in real time. For now, the CDC's advice is straightforward: wash fresh produce thoroughly, though officials caution that washing alone may not remove the parasite. Anyone with severe or persistent diarrhea, they say, should see a doctor and ask specifically about testing for Cyclospora, which standard stool panels can miss.