Why the US explosive diarrhea outbreak source remains a mystery
Health officials still cannot identify the food or water source behind a nationwide explosive diarrhea parasite outbreak across 34 US states. Nearly 7,000 cyclosporiasis cases are confirmed or under investigation, yet no grower, supplier, or product has been named despite intensive traceback work by the CDC and state partners.
Key Takeaways
- Nearly 7,000 US cyclosporiasis cases are confirmed or under investigation across 34 states, with Michigan hardest hit at more than 3,300 cases.
- No specific produce, grower, or supplier has been identified, and past outbreaks have been linked to raw fruits and vegetables.
- The cyclospora parasite takes one to two weeks to cause symptoms, making food traceback investigations exceptionally difficult.
- At least 400 cases in Michigan, Ohio, West Virginia, and Kentucky appear epidemiologically linked in a multistate cluster.
- Officials urge anyone with prolonged watery diarrhea to contact a healthcare provider and ask about cyclospora testing.
What is the explosive diarrhea parasite outbreak?
Cyclosporiasis is an intestinal illness caused by the microscopic Cyclospora parasite. People become infected by consuming contaminated food or water, and the main symptom is frequent, watery, and sometimes explosive diarrhea, according to the Centers for Disease Control and Prevention.
The CDC said on Tuesday that 1,645 people nationwide were confirmed to have cyclosporiasis, with another 5,100 cases under investigation. No deaths have been reported, though 141 patients have been admitted to hospital. The illness is not usually life-threatening, but symptoms can last from a few days to over a month without treatment.
How many states and people are affected?
The outbreak has spread to 34 states. Michigan and Ohio have been hit particularly hard, with the two states reporting more than 3,000 cases combined. Michigan alone accounts for over 3,300 cases, followed by New York state, which has reported 510 cases with more than half coming from New York City alone.
Other states with large case numbers include Indiana, Texas, and New Jersey, according to the CDC. More than 400 cases across Michigan, Ohio, West Virginia, and Kentucky appear linked in a multistate cluster, with sick people reporting symptoms on or after June 22, 2026. The true number of infections is likely higher because some people recover without medical care and are never tested.
Why can't officials find the outbreak source?
Those infected became sick after eating food in the United States and did not report travel during the 14 days before illness, the CDC said. Yet no specific type of produce, grower, or supplier has been identified. Contamination typically occurs at the farm or irrigation level, making traceback investigations difficult, epidemiologist Dr Caitlin Rivers wrote.
Experts told the BBC the parasite is notoriously difficult to trace. Unlike most foodborne illnesses that cause symptoms within hours, cyclospora takes one to two weeks to make people ill, so patients may not remember everything they ate. Given the scale of the outbreak, public health experts said there were likely multiple points of contamination in the food supply.
Previous cyclospora outbreaks in the US and Canada have been linked to bagged salad mixes, fresh cilantro, basil, raspberries, snow peas, and green onions. Some experts also noted that federal surveillance cuts, including scaled-back FoodNet monitoring for cyclospora, have left investigators with less data than in past outbreaks.
What should Americans do to protect themselves?
Health officials have advised the public to thoroughly wash produce, avoid certain fruits like raspberries, and cook vegetables when possible to kill the pathogen. Michigan's health department has recommended that restaurants reduce risk by washing greens, cooking raspberries and leafy greens when possible, and removing outer layers of lettuce and green onions.
Person-to-person transmission does not occur with cyclosporiasis. Officials urge anyone experiencing prolonged watery diarrhea to contact a healthcare provider and specifically ask about cyclospora testing on stool samples. Local health officials may also contact sick patients to learn what they ate in the two weeks before falling ill.
As investigators continue interviewing thousands of patients, the case counts are expected to keep rising. For more coverage of baffling public health mysteries, see our True Crime & Unsolved Mysteries section.