What is cyclosporiasis, the parasitic illness causing 'explosive' diarrhea in the US?
Cases of cyclosporiasis, a parasitic illness that can cause severe, watery diarrhea, have surged across parts of the United States in recent days, health officials say. Michigan alone has reported an outbreak of nearly 1,000 cases, making it the largest in the state's history, while Ohio has also recorded a sharp rise, with 177 cases as of early July.
The illness is caused by a microscopic parasite called Cyclospora cayetanensis, which spreads when a person consumes food or water contaminated with the parasite's egg-like cysts. It cannot be passed directly from person to person the way many respiratory or viral illnesses can, meaning outbreaks typically trace back to a shared contaminated food or water source.
Symptoms usually begin about a week after exposure and can include frequent, watery diarrhea often described by patients as "explosive," along with loss of appetite, weight loss, cramping, bloating, nausea and fatigue. Some infected people experience only mild symptoms, while others suffer for weeks if the infection goes untreated.
Unlike many foodborne illnesses that resolve within a few days, cyclosporiasis can drag on far longer without treatment, sometimes lasting more than a month. The parasite does not respond to the antibiotics typically used for common bacterial stomach bugs, and doctors instead prescribe a specific antiparasitic medication once the infection is confirmed.
The US Centers for Disease Control and Prevention says cyclosporiasis is rarely life-threatening in otherwise healthy adults, though it can pose greater risks to young children, older adults and people with weakened immune systems, who may become severely dehydrated from prolonged diarrhea.
Outbreaks in the US have historically been linked to imported fresh produce, particularly leafy greens, herbs and berries grown in regions where irrigation water may carry the parasite. Health investigators typically interview affected patients about their recent food history in an effort to trace the outbreak back to a specific product or supplier.
Because the parasite is resistant to standard chlorine-based water treatment used in many food-processing and restaurant settings, thorough washing does not always eliminate contamination on produce, particularly on leafy vegetables with folds or crevices where cysts can lodge.
Health departments in affected states are working with federal investigators to identify a common source behind the current cluster of cases, though officials say pinpointing the exact origin of a cyclosporiasis outbreak can take weeks, since symptoms appear well after exposure and the parasite is difficult to detect using routine lab tests.
Doctors recommend that anyone experiencing prolonged watery diarrhea, particularly lasting more than a few days, see a healthcare provider and mention recent travel or consumption of imported fresh produce, since standard stool tests do not always screen for Cyclospora unless specifically requested.
While the current outbreak has drawn attention because of its size, cyclosporiasis is not a new phenomenon in the US, with smaller clusters reported most summers, generally tied to the seasonal import of certain fresh produce. Health officials say the parasite remains a useful reminder of how modern, globalized food supply chains can turn a single contaminated batch into a multi-state health event.
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