An alarming surge in gastrointestinal illness, characterized by sudden and severe diarrhea, is being reported in regions including southeast Michigan and northern Ohio. The culprit is identified as the parasite Cyclospora cayetanensi.
Michigan health officials have documented 1,251 cases of cyclosporiasis, a dramatic increase that more than doubles the number reported just before the July 4 holiday. This figure far surpasses the typical annual average of around 50 cases. An initial cluster of 170 cases was noted by state officials in late June, with numbers since escalating significantly. Among the confirmed cases in Michigan, 44 individuals have required hospitalization.
Neighboring Ohio counties, particularly those adjacent to southeast Michigan, are also observing a substantial number of cases, exceeding 500. Lucas County alone accounts for 306 of these. However, the Ohio Department of Health reported a statewide total of 177 cases as of July 2, with 28 hospitalizations. The majority of these cases have emerged since June 20.
In response to the outbreak, health authorities are advising food establishments. The Michigan Department of Health & Human Services (MDHHS) has issued recommendations for enhanced produce washing procedures for restaurants and commercial kitchens in southeast Michigan. These guidelines emphasize thorough cleaning of items such as lettuce, herbs, green onions, raspberries, and snow peas, all of which have been linked to previous Cyclospora outbreaks.
The MDHHS noted that while cyclosporiasis is typically not life-threatening, severe dehydration resulting from frequent diarrhea can pose risks, especially for vulnerable populations like young children, the elderly, and those with compromised immune systems. The incubation period for the illness is generally about a week, but can range from two days to over two weeks. Symptoms can be intermittent, resolving and then returning, and the illness can persist for weeks.
Concerns about the completeness of national data are also being raised. As of July 1, 2025, the Centers for Disease Control and Prevention’s (CDC) FoodNet program, a key surveillance system for foodborne illnesses, has made tracking Cyclospora an optional rather than mandatory reporting requirement. Currently, state health departments are only mandated to track Salmonella and Shiga toxin–producing Escherichia coli (STEC), as these are responsible for the largest foodborne outbreaks in the U.S. Some states, like Michigan, have chosen to continue their own Cyclospora surveillance. The CDC’s national data also appears to lag, with their most recent update on July 1 showing only 145 cases nationwide through June 16.