A widespread outbreak of the diarrhoea-causing parasitic infection cyclosporiasis has swept across more than a dozen U.S. states in recent months, driving a sharp spike in reported cases and prompting public health alerts from local and federal agencies.
Cyclosporiasis, an intestinal infection triggered by the microscopic Cyclospora parasite, is primarily contracted through the consumption of food or water contaminated with the pathogen. The most defining symptom of the infection is frequent, watery, and often explosive diarrhoea. While the illness is rarely fatal, it can linger for weeks if left untreated, and symptoms may reoccur after initially fading, with an average incubation period of around one week after exposure. Unlike many common infectious diseases, the infection cannot spread directly between people; transmission only occurs via the faecal-oral route through contaminated food or water, according to Dr. Caitlin Rivers, an epidemiologist from the Johns Hopkins Center for Health Security.
The U.S. Centers for Disease Control and Prevention (CDC) has confirmed that outbreaks have been documented across 17 states since early May, including large population states such as Illinois, New York, and Texas. Between May 1 and June 16, the latest window for which the CDC has released aggregated national data, 145 confirmed cases were reported nationwide, with 20 patients requiring hospital admission. No fatalities linked to the current outbreak have been recorded to date.
State-level data compiled in early July tells a far starker picture of the outbreak’s spread, with case counts far outpacing the CDC’s aggregated national figures. As of July 8, Michigan alone had recorded nearly 1,000 confirmed cyclospora cases within a single two-week period, making it the epicenter of the ongoing outbreak. Neighboring Ohio has reported 177 cases, while Illinois logged 141 cases by July 7 — a number state health officials described as “higher-than-average” compared to typical seasonal infection rates.
Public health experts note that the actual number of infections across the country is almost certainly higher than official counts. Many people with mild cases recover at home without seeking medical care, meaning their infections are never officially diagnosed or reported.
Investigators have not yet identified the specific source of the current outbreak, a common challenge in cyclospora investigations, according to health experts. Contamination of fresh produce typically occurs at the farm level, often during irrigation or pre-harvest handling, which makes tracing the source of the pathogen difficult. Past outbreaks of cyclosporiasis in the U.S. and Canada have been linked to contaminated raw produce including pre-packaged bagged salad mixes, fresh cilantro, basil, raspberries, snow peas, and green onions. To date, no specific produce variety, grower, or supplier has been tied to the current outbreak.
In response to the rising case counts, Michigan’s state health department has issued guidance for food service operations, urging restaurants and commercial kitchens to reduce infection risk by thoroughly washing leafy greens, cooking raspberries and leafy greens when possible, and discarding the outer layers of lettuce and green onions before serving. This guidance comes amid a minor divergence in federal recommendations: while the U.S. Food and Drug Administration notes that rinsing produce alone is rarely effective at removing Cyclospora, the CDC still maintains that thorough washing is a recommended precaution.
For members of the public, health officials are urging anyone experiencing persistent watery diarrhoea to contact a healthcare provider to get tested for the infection, even as they emphasize that the illness remains far less common than other foodborne pathogens such as salmonella and E. coli.