Cyclospora cayetanensis is a single-celled parasite too small to see, spread when people swallow it in contaminated food or water. Unlike bacteria, it does not multiply inside the human gut; each ingested oocyte must mature before it can cause illness. The result is a distinctive, relapsing course of watery diarrhea, cramping, nausea and fatigue that can drag on for weeks if untreated — earning it the blunt nickname "explosive diarrhea" in coverage of the current outbreak.
In 2026 the US Centers for Disease Control and Prevention has logged cyclosporiasis cases in more than 30 states, with totals running well above the roughly 2,800 cases the agency has averaged per year since 2016. Individual state investigations have reported clusters in the hundreds. No single food has been officially confirmed as the source, but past US outbreaks have repeatedly traced back to fresh produce — cilantro, basil, salads, berries and imported produce are among the recurring suspects, because the parasite survives washing and is not killed by simple rinsing.
The harder problem is detection. Cyclospora is not part of the routine lab panels that clinics run for diarrhea, so cases are easy to miss unless a doctor specifically orders the right test. That blind spot, combined with the parasite's long and erratic incubation, makes it difficult to link scattered patients to one shipment of contaminated food. Investigators are now using genetic fingerprinting of parasite samples and detailed food histories to narrow the trail — a reminder that food safety for fresh produce depends as much on tracing as on washing.
Knowledge takeaway: Cyclospora cayetanensis is a microscopic parasite spread through contaminated food or water that causes a prolonged, relapsing diarrheal illness lasting weeks if untreated; US cases in 2026 have surpassed 30 states and run above the CDC's ~2,800 annual average since 2016, yet no single contaminated food has been officially confirmed; the parasite is missed by standard diarrhea lab tests and survives routine washing, so detection and produce traceability — not just rinsing — are the weak points investigators are racing to close.