Michigan health officials are investigating an unusually large outbreak of cyclosporiasis after 174 cases were reported across southern Michigan between June 22 and June 30, 2026. The illness is caused by the parasite Cyclospora cayetanensis and can lead to stomach-related symptoms, including severe diarrhea.
According to the Michigan Department of Health and Human Services (MDHHS), the number of infections reported in little more than a week is far higher than what the state normally sees in an entire year. Officials have not yet identified the source of the outbreak but expect more cases to be reported as the investigation continues.
Michigan searches for outbreak source
The outbreak has been concentrated in several southern Michigan counties, with Monroe County reporting the highest number of cases. State data shows 70 cases in Monroe County, 33 in Lenawee County, 21 in Washtenaw County, 12 in Wayne County, and seven each in Jackson and Shiawassee counties. Another 24 cases have been recorded across 11 additional counties and the city of Detroit.
MDHHS spokesperson Lynn Sutfin said health officials are still trying to determine where the infections originated. Speaking on behalf of the department, Sutfin said, “Individuals concerned about sudden gastrointestinal illness should contact a health care provider.
Cyclospora infections can be treated with antibiotics and individuals experiencing diarrheal illness or vomiting are encouraged to hydrate, particularly during the high temperatures expected this week.”
The Michigan Department of Agriculture and Rural Development is also helping with the investigation. The agency has advised residents to wash fresh produce carefully, remove damaged sections of fruits and vegetables, and refrigerate produce after it has been cut.
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CDC explains symptoms and spread of cyclosporiasis
According to the Centers for Disease Control and Prevention (CDC), symptoms can appear anywhere from two days to two weeks after infection. The illness often causes watery diarrhea and can sometimes lead to frequent or explosive bowel movements. Other symptoms may include nausea, vomiting, stomach cramps, bloating, low-grade fever, loss of appetite, and weight loss.
The CDC says the parasite is commonly spread through contaminated food or water. Person-to-person transmission is considered unlikely. In recent years, several outbreaks in the United States have been linked to contaminated fresh produce, especially during the summer.
The recent spike stands out because Michigan has reported relatively low numbers of cyclosporiasis cases in recent years. State surveillance records show 56 cases in 2022, 43 in 2023, 41 in 2024, and 54 in 2025.
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The increase is not limited to Michigan. Just south of the state line, the Toledo-Lucas County Health Department in Ohio reported around 65 cases of the illness as of Wednesday morning. Michigan health officials said the current cases involve patients between the ages of 8 and 84, with a median age of 41.
