Health officials have not identified a source as cases rise sharply in southeast Michigan and nearby Ohio.
LANSING, Mich. — Michigan health officials are investigating the state’s largest known cyclosporiasis outbreak after more than 1,200 people were diagnosed with the intestinal illness, including dozens who were hospitalized.
The outbreak has grown quickly since late June, when the Michigan Department of Health and Human Services first reported more than 170 cases in seven counties. State officials now say the case count has reached 1,251, with 44 hospitalizations. No deaths have been reported. The source remains unknown, but investigators are focused on food or water exposure, including fresh produce often eaten raw.
State officials announced the outbreak July 1, saying cases had appeared in Monroe, Lenawee, Washtenaw, Wayne, Livingston, Shiawassee and Jackson counties over a nine-day period. The numbers soon expanded across southeast Michigan and then beyond. Dr. Natasha Bagdasarian, Michigan’s chief medical executive, said officials expected more illnesses because of the unusual pace of reports. “Based on the unusual number of cases we have identified in a little over a week, we anticipate additional cases of illness being reported,” Bagdasarian said. Michigan usually identifies about 50 cyclosporiasis cases in a full year.
Cyclosporiasis is caused by Cyclospora cayetanensis, a microscopic parasite that infects the small intestine. The illness can cause frequent watery diarrhea, cramps, nausea, fatigue, loss of appetite and bloating. Symptoms often begin two to 14 days after exposure and can last for weeks if untreated. Health officials say the parasite is commonly linked to food or water contaminated with feces. It is not known to spread directly from one person to another. Officials have not named a grower, supplier, restaurant chain or single produce item as the source of the Michigan outbreak.
The investigation has also reached Ohio, where counties near the Michigan border have reported large numbers of illnesses. Lucas County, which includes Toledo, has reported hundreds of cases, and northwest Ohio has recorded more than 500. Federal and state health officials are reviewing illness reports in other states as well. The Centers for Disease Control and Prevention has tracked cyclosporiasis activity in multiple states this summer, though state and local counts can change faster than national updates. Investigators are comparing food histories, purchase records and illness dates to look for a common link.
Michigan officials said fresh produce remains a leading concern because past Cyclospora outbreaks in the United States have been tied to foods such as lettuce, herbs, berries, green onions and snow peas. The parasite can be difficult to trace because people may not become sick until days after eating contaminated food. By then, produce may have been eaten, thrown away or moved through several suppliers. Testing also can be difficult because Cyclospora is not always found by routine stool exams unless a provider orders specific testing.
The state health department and the Michigan Department of Agriculture and Rural Development are working with local health departments on interviews, lab testing and food supply reviews. Officials have also issued added instructions for restaurants and commercial kitchens that prepare raw produce in southeast Michigan. Those steps include more careful handling of leafy greens, herbs and other raw items that have been linked to past outbreaks. Officials said the guidance is part of the investigation and does not mean a specific food has been confirmed as the source.
The outbreak has disrupted some food service operations while investigators search for answers. Some restaurants in affected areas have temporarily pulled or limited fresh items, including lettuce and herbs, as a precaution. State officials have not confirmed a link between any restaurant brand and the outbreak. Public health agencies are still trying to determine whether illnesses came from one contaminated product, several products or separate exposures during the same period. Bagdasarian said the pattern shows a linked outbreak, but the exact pathway has not been established.
Cyclosporiasis outbreaks are most common in late spring and summer. Public health experts say the number of reported cases has risen in recent years as testing improves and contaminated produce moves through wider supply chains. Michigan’s current outbreak stands out because of its speed and size. The count rose from more than 170 cases announced July 1 to more than 1,200 by July 9. That increase made it the largest recorded cyclosporiasis outbreak in Michigan history and one of the largest U.S. outbreaks in recent years.
The next phase of the investigation will focus on matching illness timelines with food distribution records and lab results. State and local health departments are continuing interviews with patients, while federal partners monitor reports from other states. Officials have not announced a date for a final report. The case count may keep changing as more test results return and as doctors identify patients whose symptoms began earlier. For now, the outbreak remains active, with the highest impact in southeast Michigan.
Michigan officials said the investigation remains open as of July 9. The next milestone will be the state’s next case update, which is expected to show whether new illnesses are slowing or continuing to rise.
Author note: Last updated July 9, 2026.