Cyclosporiasis Outbreak Passes 1,400 Cases as Investigators Admit They Still Can't Trace the Source

A parasite that causes weeks of relapsing, explosive diarrhoea has now sickened more than 1,400 people across Michigan and Ohio, and investigators still can't say where it's coming from, leaving families across the US midwest exposed at the height of produce-and-pool season.

Cyclosporiasis, caused by the microscopic parasite Cyclospora cayetanensis, has hit Michigan hardest. State officials confirmed 1,251 cases as of Thursday, up from about 50 in a normal year. While Ohio has officially confirmed 177 cases statewide due to lagging data, local tracking in counties bordering Michigan has already surged past 500, including 306 cases in Lucas County alone.

The Michigan Department of Health and Human Services and the Ohio Department of Health both say no common food, grower, or supplier has been identified. The Centers for Disease Control and Prevention (CDC) is working with the Food and Drug Administration (FDA) and local officials on the traceback, which can take months and sometimes never lands on an answer.

The Pool Risk Nobody's Talking About

Cyclospora parasites, which resist standard chlorination, can survive in swimming pools, splash pads, and natural water sources, posing a risk during outbreaks. While Cyclospora is primarily transmitted through produce, health experts advise avoiding public swimming areas if a major outbreak is active locally.

It's a warning that cuts against the season. Families heading to the pool to escape July heat assume chlorine kills everything. For this parasite, it doesn't. While washing alone fails to remove it, cooking produce to an internal temperature of 158 degrees Fahrenheit (70° C) does kill it, according to Michigan health guidance.

Why the Official Numbers Are Weeks Behind

There's a second problem, and it's about the data itself.

The most recent national CDC surveillance counted just 145 cases across 17 states between 1 May and 16 June, and that figure lags Michigan entirely. Michigan alone now reports nearly ten times that. NBC News' own running tally has already cleared 2,000 cases nationwide.

Cyclospora infections are challenging to diagnose because standard stool tests often fail to detect them, requiring specific, named orders for PCR assays or modified acid-fast stains. Michigan's chief medical executive, Dr Natasha Bagdasarian, confirmed a linked, rapidly spreading outbreak to the Associated Press, noting that many cases are initially misdiagnosed as viruses.

What This Costs Families Right Now

This isn't a 24-hour stomach bug. Untreated cyclosporiasis can drag on for weeks or even a month, often improving for a few days before returning, according to the CDC. That relapsing pattern means lost work, disrupted childcare, and mounting medical bills.

The fix is cheap once it's diagnosed. Treatment is a course of the generic antibiotic trimethoprim-sulfamethoxazole, sold as Bactrim or Septra, and it costs very little. The catch is the diagnosis, which relies on a doctor knowing to look. Officials advise anyone with watery diarrhoea lasting beyond 48 hours, especially with a wax-and-wane pattern, to see a physician and ask about Cyclospora directly.

There's also confusion on the ground. Signs at some Michigan Taco Bell locations told customers the chain couldn't sell lettuce, cilantro, onion, pico de gallo, and guacamole because of a 'nationwide recall'. The FDA has issued no such recall in the past two months, and Taco Bell has not confirmed one. For now, the source of the largest US Cyclospora surge in years remains a mystery, and the case count keeps climbing.