What Is Cyclospora? Inside The Parasite Outbreak Spreading Across The US

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In Michigan, health officials expected to see roughly 50 cases of a stomach illness this year. By early July, they had counted more than 1,500.

That illness is cyclosporiasis, caused by a microscopic parasite called Cyclospora cayetanensis. Across the United States, more than 4,000 cases have now been reported this summer, according to a tally by NBC News based on state health department data, while the Centers for Disease Control and Prevention had received reports of 843 cases as of Thursday, spread across 31 states. The gap between the two numbers says something important about how outbreaks like this are tracked - and why this one has proven so hard to pin down.

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What Is Cyclospora?

Cyclospora is a single-celled parasite that lives in the human gut. People become infected by consuming food or water contaminated with faeces carrying the parasite, often via fresh produce that has been washed with, or grown near, contaminated water.

Cases climb every year during the spring and summer months, with the season typically running from May through August. What has caught health officials off guard this year is the sheer scale of it.

Why This Year Looks Different

Michigan alone has logged over 1,500 cases and at least 44 hospitalisations - 31 times the roughly 50 cases the state usually records annually.

Dr Natasha Bagdasarian, Michigan's chief medical executive, said the state was bracing for the number to climb further.

"We anticipate additional cases of illness being reported," she said, urging anyone with sudden, ongoing diarrhoea to contact their doctor.

Nationally, the picture is murkier. Dianna Blau, acting chief of the CDC's Parasitic Disease Branch, told NBC News the US recorded around 2,700 cases in all of 2025 - a number this year's outbreak has already blown past, with weeks of peak season still to go.

So What's Causing It?

That's the part investigators haven't cracked yet. Previous US outbreaks of cyclosporiasis have been linked to raspberries, basil, cilantro, snow peas and lettuce, according to the Food and Drug Administration, and federal investigators are currently examining supply chains for onions, cucumbers and cilantro. But officials have been careful not to draw a straight line between this year's cases.

The CDC said in a July update that it has "no evidence of a single, multistate Cyclospora outbreak linking cases happening right now and being reported in the press." Instead, investigators believe several separate clusters, possibly with different sources, may be driving the surge simultaneously - which makes tracing any one culprit far harder.

Symptoms To Watch For

Cyclosporiasis symptoms typically appear about a week after infection, which is part of why the source is so tricky to identify. They include:

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• Watery diarrhoea, sometimes described as explosive
• Loss of appetite and weight loss
• Stomach cramps and bloating
• Nausea, fatigue and, less commonly, low-grade fever
• Standard stool tests often miss the parasite, so doctors need to specifically request testing for Cyclospora in patients with persistent, unexplained diarrhoea.

How To Protect Yourself

• Wash all fresh produce, including herbs, thoroughly under running water
• Scrub firm fruit and vegetables such as melons and cucumbers with a clean brush
• Cook produce where possible - heating food to 158°F (70°C) kills the parasite
• Avoid swallowing water from pools, lakes or other untreated sources
• Wash hands before and after handling food, especially if you're unwell

The illness does not spread person to person, so isolation isn't necessary - but anyone symptomatic should be extra careful with hand hygiene before preparing food for others.

Disclaimer: The information provided in this article is for general informational and educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or a qualified healthcare provider with any questions you may have regarding a medical condition.