Cases of a Parasitic Infection That Can Cause Diarrhea for Weeks Are Rapidly Rising in the U.S. Here's What to Know

Health officials across the United States are tracking a sharp rise in cyclosporiasis, a gastrointestinal illness caused by a microscopic parasite that can trigger diarrhea lasting for weeks. The uptick has been described as unusually steep even for a season when the infection is known to circulate, and investigators have not yet pinned down exactly where the current wave originated.

The culprit is Cyclospora cayetanensis, a single-celled parasite too small to see without a microscope. It typically enters the food or water supply when produce or irrigation sources come into contact with feces, most often traced back to agricultural settings. Once ingested, it can cause severe intestinal distress, including watery, frequent bowel movements that some patients and clinicians have characterized as sudden and forceful.

What sets this year apart is the scale. In a typical year, the country as a whole logs only a few hundred confirmed cyclosporiasis cases. Michigan alone has already surpassed 1,500 reported cases in 2026, a figure that dwarfs the historical national average on its own. Health departments in other states have likewise flagged case counts well above what they would normally expect at this point in the year, suggesting the outbreak is not confined to a single region.

Investigators are still working to identify the specific source, or sources, behind the surge. Because the parasite spreads through contaminated produce or water rather than person-to-person contact, tracing an outbreak often means reviewing supply chains, farm practices, and shipping routes for fresh fruits and vegetables sold across multiple states. That process can take weeks, particularly when a product has already moved through several distributors before symptoms begin appearing in patients.

Timing is a notable factor as well. Cyclosporiasis cases tend to climb during the late spring and summer months, a pattern tied to the growing and harvesting seasons for produce that is more likely to carry the parasite if contaminated. That seasonal backdrop means health officials were already primed to watch for cases, but the current numbers are running well ahead of the usual curve even accounting for the time of year.

The illness itself, while unpleasant, is generally treatable. Symptoms can include prolonged diarrhea, cramping, bloating, nausea, and fatigue, sometimes stretching on for weeks if left untreated. Antibiotic regimens are available and effective for most patients, though the extended duration of untreated symptoms is part of what makes the parasite notable compared to more short-lived foodborne illnesses.

Public health experts are urging consumers to take precautions in the meantime, chiefly by thoroughly rinsing all fresh produce before eating it, even items that will be peeled. That guidance applies broadly, since contamination is not always visible and can affect a wide range of fruits and vegetables depending on where and how they were grown. Officials have not identified a single product to avoid, underscoring that the investigation into the outbreak's origin remains ongoing. Consumers experiencing prolonged digestive symptoms are advised to consult a healthcare provider, particularly given how easily cyclosporiasis can be mistaken for other, less persistent stomach bugs.

As case counts continue to be reported through the summer, health agencies are expected to provide updates on both the scope of the outbreak and any progress in tracing its source, with the outcome likely shaping produce-safety guidance for future growing seasons.

Source: Smithsonian Magazine