A parasite that causes ‘explosive’ diarrhea is spreading across the U.S. and now cases have been reported in Colorado

If you thought altitude sickness was the worst thing Colorado could do to your gut, allow us to introduce Cyclospora — a microscopic fecal parasite currently making national headlines for causing what the CDC is officially describing as “explosive” diarrhea.

The agency is investigating more than 1,000 cases of cyclosporiasis across at least 18 states, and Colorado is on the list. Preliminary data from the Colorado Department of Public Health and Environment show 90 cases recorded statewide since January, a 23% jump from the 73 cases logged over the same period in 2025. The state reported 204 total cases last year.

Before you panic and swear off every farmers market salad, CDPHE wants you to know Colorado is on the lower end of the national map. Michigan is the real epicenter, with more than 700 cases exploding (pun intended) in a single week around the Fourth of July. Colorado is not currently linked to any of the multistate clusters the CDC and FDA are investigating, and CDPHE spokesperson Hope Shuler told Denver7 the majority of Colorado’s cases involve people who recently traveled internationally. “At this time, Colorado does not have cases in any multistate outbreaks being investigated by CDC and FDA,” the agency said. So while the Centennial State isn’t exactly ground zero, it’s also not exactly in the clear.

The culprit, Cyclospora, hitches a ride on raw produce — think basil, cilantro, bagged salad mixes, raspberries and snow peas — contaminated with, well, feces. It does not spread person to person, so your coworker’s suspicious post-lunch sprint to the bathroom is not going to take down the whole office. The bad news: washing your produce can reduce dirt and germs but may not actually remove the parasite, according to CDPHE. The good news: cooking food to at least 158 degrees Fahrenheit kills it. The illness is treatable with the antibiotic Bactrim, typically prescribed for 10 days.

For Coloradans who pride themselves on their farm-to-table lifestyles and weekend hauls from Boulder, Cherry Creek and Union Station farmers markets, the CDC’s advice is straightforward: scrub your produce thoroughly with a brush, refrigerate prepared fruits and vegetables within two hours, and cook when you can. If you develop persistent watery diarrhea — the “explosive” kind or otherwise — see a doctor and request a stool sample test, because Cyclospora doesn’t show up on standard screenings. The parasite’s peak season runs from May through summer, so Colorado’s numbers could still climb before the first cold snap.