A parasitic infection known for triggering severe, “explosive” diarrhoea has surged past 700 confirmed cases in Michigan alone, according to state health officials, marking one of the largest and fastest-moving outbreaks of its kind in years and prompting a multistate investigation by federal authorities.
The outbreak of cyclosporiasis, caused by the microscopic parasite Cyclospora cayetanensis, has spread rapidly since it was first flagged in late June, when the Michigan Department of Health and Human Services reported roughly 170 cases across seven counties. By July 4, that count had jumped to 572. Two days later, it climbed again to 681, and by Tuesday, the state’s tally had surpassed 700, a more than fourfold increase in barely a week. At least 20 people have been hospitalised nationwide, though no deaths have been reported.
“Michigan typically identifies 50 cases a year,” a department spokesperson told TODAY.com, underscoring how far outside the norm this summer’s numbers fall.
A Mystery Source, and a Familiar Culprit
Cyclosporiasis is typically spread through food or water contaminated with faeces and does not usually pass from person to person, according to health officials. The Centres for Disease Control and Prevention has previously linked American outbreaks to fresh produce including basil, cilantro, raspberries and snow peas, and a 2022 cluster in Florida was traced to bagged romaine lettuce in a prepackaged salad kit.
So far, though, investigators have not pinpointed a single cause behind this year’s surge. “As of July 4, 2026, no specific produce grower/supplier, or specific produce type, has been identified as the source of the outbreak,” the Michigan health department said in a statement. The CDC, which is coordinating with the Food and Drug Administration and state officials, said in a July 1 update that there is currently no evidence tying all of the reported illnesses to one common source.
Dr. Natasha Bagdasarian, Michigan’s chief medical executive, said the sheer volume of cases is complicating efforts to trace the outbreak’s origin. “So we have 700 people who need to be interviewed, which makes things significantly more complicated,” she said, adding that contaminated produce remains investigators’ leading theory. Bagdasarian said earlier in the outbreak that her team expected additional cases to surface as testing continued.
Symptoms Can Take Two Weeks to Appear
The illness’s hallmark symptom is watery diarrhoea that the CDC describes as “frequent and sometimes explosive,” often accompanied by loss of appetite, abdominal cramping, bloating, nausea, vomiting and low-grade fever. Symptoms can take anywhere from two to fourteen days to appear after exposure, making it difficult for patients and investigators alike to identify what food or water may have caused an infection.
Haley Hompstead, a resident of Monroe County, one of the hardest-hit areas in the state, described the sudden onset of her symptoms, which began July 3. “The morning of the 3rd, I got woken up at about seven in the morning with the most, like, excruciating abdominal pain I’ve ever had,” she said.
Cases Spreading Well Beyond Michigan
The outbreak is not confined to Michigan. Illinois health officials have reported a higher-than-average number of cyclosporiasis cases in recent weeks, while Ohio has logged at least 170 infections since late June. Indiana, New York and North Carolina have each reported more than 100 cases in recent weeks as well, and officials in Illinois said they have not yet identified a single source linking the various clusters.
Health officials note that cyclosporiasis is considered a seasonal illness in the United States, with cases typically peaking between May and August, and some increase in the summer months is expected. But the scale of Michigan’s spike, in particular, has put state and federal investigators on high alert.
Washing Isn’t Enough — Cooking Is the Only Sure Fix
The CDC warns that because the Cyclospora parasite is microscopic and can lodge in tiny crevices on produce, thorough washing may reduce but not eliminate the risk of infection. Cooking, health officials say, remains the only reliable way to kill the parasite. Michigan officials have advised residents to buy whole heads of lettuce rather than pre-washed bagged greens, discard the outer leaves, and rinse remaining leaves thoroughly under running water, cooking leafy greens when possible.
Health officials in both Michigan and Illinois are urging anyone experiencing sudden or persistent diarrhoea to contact their healthcare provider and are asking residents to report cases to local health departments to assist in the ongoing investigation.
