Cyclospora infections rise in the U.S. most often during late spring and summer, typically linked to contaminated fresh produce and marked by prolonged watery diarrhea. This summer, Michigan has emerged as the center of one of the country’s largest outbreaks in years, with state and neighboring Ohio officials reporting a fast-growing case count.
Michigan reports the largest outbreak in state history
Michigan health officials said on July 8 that the state’s Cyclospora outbreak had reached 992 confirmed cases, a total that pushed the regional outbreak past 1,000 when combined with neighboring Ohio figures reported the same day. The Associated Press, citing the Michigan Department of Health and Human Services, reported about 40 hospitalizations and no deaths. State officials have described it as the largest Cyclospora outbreak in Michigan history.
The outbreak was first publicly announced by the Michigan Department of Health and Human Services on July 1, when the agency said it was investigating more than 170 cases identified since June 22 in southeastern Michigan. Michigan typically records only about 50 cases in a full year, according to the state health department. The speed of the increase has made the outbreak stand out even against the seasonal pattern public health officials usually expect.
Dr. Natasha Bagdasarian, Michigan’s chief medical executive, told the AP there is “clearly a linked outbreak happening right now,” even though the precise source has not been identified. Public health investigators are working with the Michigan Department of Agriculture and Rural Development and local health departments as they trace possible food exposures. As of July 8, officials had not tied the illnesses to a single restaurant chain, grocery retailer, farm or distributor.
Michigan officials initially said the known cases were concentrated in the southeastern part of the state, and that remains the clearest confirmed geographic focus. The state has not released a comprehensive public list of affected counties, stores or restaurants, and officials have said the source remains under investigation. That means residents know the outbreak is regional, but not yet which specific food supply channel may be responsible.
Just across the border, Lucas County, Ohio, reported 306 cases as of July 8, according to the AP, while northwest Ohio overall had recorded more than 500 cases. Axios also reported Ohio was among multiple states logging Cyclospora illnesses this season, though the Michigan-Ohio corridor appeared to be carrying the heaviest burden so far. The cross-border pattern has added to suspicions that a shared produce distribution route may be involved, though officials have not confirmed that conclusion.
Federal health officials have said this is not considered a national public health emergency. CDC information cited by AP indicated the national case total at this point in the year is about four times higher than at the same point in 2025, although federal surveillance data can lag state reporting. That makes the Michigan and Ohio numbers significant locally while leaving the broader national picture still incomplete.
Cyclospora cayetanensis is a microscopic parasite that causes cyclosporiasis, an intestinal illness whose most common symptom is watery diarrhea, according to the CDC. The CDC says symptoms can also include loss of appetite, weight loss, cramping, bloating, nausea, fatigue and low-grade fever. The illness is generally treated with antibiotics and is not usually life-threatening, but symptoms can last for days or even weeks without treatment.
Health officials say Cyclospora is commonly spread through food or water contaminated with feces, and prior outbreaks have been associated with fresh produce including herbs, lettuce and berries. Investigators often face delays because the parasite can be difficult to detect, cannot be readily grown in laboratory settings, and may be tied to a single ingredient used across many meals. Researchers cited by the AP also said underreporting remains a challenge because some gastrointestinal testing panels do not specifically look for Cyclospora.
While the source remains unknown, Michigan officials have issued practical guidance as the investigation continues. The state has advised residents to buy whole heads of lettuce instead of prewashed bagged lettuce or salad mixes, remove the outer two or three leaves, and wash the remainder under running water before eating. The CDC also says people with ongoing diarrhea should speak with a health care provider, a step that may shape how quickly additional cases are identified in the days ahead.