Nearly 1,000 people in Michigan have been diagnosed with a parasitic infection that causes weeks of watery diarrhea, making it the largest such outbreak in state history and one of the nation's largest in years. No deaths have been reported, and the source of the cyclospora infections has not been identified. Investigations into similar illnesses are ongoing in 28 other states, including Ohio, where cases are also rising near the Michigan border.
Outbreak Statistics and Spread
Michigan officials first announced the outbreak last week, with over 170 cases in the southeastern corner of the state since June 22. By Wednesday, the state reported 992 cases, including about 40 hospitalizations. In Lucas County, Ohio, 306 cases were reported, with over 500 cases across northwest Ohio. Michigan typically identifies only about 50 cases per year.
Dr. Natasha Bagdasarian, Michigan's chief medical executive, told the Associated Press that “there is clearly a linked outbreak happening right now.” The surge has prompted health officials to warn residents and investigate potential food sources.
What Is Cyclospora?
Cyclospora is a microscopic, spherical parasite that commonly causes watery diarrhea “with frequent and sometimes explosive bowel movements,” according to the U.S. Centers for Disease Control and Prevention. The illness, cyclosporiasis, is not usually life-threatening and is typically treated with antibiotics. Outbreaks tend to occur in late spring and summer.
The parasite infects the bowels and spreads through feces. Past outbreaks have been linked to fruits or vegetables exposed to contaminated irrigation water. Cyclospora is less common than salmonella or E. coli, but cases have risen over the past decade, with spikes in 2018 and 2019 attributed to climate change and better detection.
Comparison to Previous US Outbreaks
Comprehensive data on cyclospora outbreaks is limited, but only a few documented outbreaks in the last 20 years have surpassed 1,000 cases. These include a 1997 outbreak linked to Guatemalan raspberries that sickened over 1,000 in the U.S. and Canada, and a 2019 outbreak tied to Mexican basil that sickened more than 2,400.
Melanie Firestone, a University of Minnesota foodborne illness researcher, noted that underreporting is common because some tests don't detect cyclospora. Additionally, the parasite cannot be grown in labs, making it hard to trace contaminated produce. Shared ingredients like basil or cilantro can complicate source identification, and food distributors may send contaminated products to both stores and restaurants.
Current Situation and National Context
Cases are surging in and around southeastern Michigan, but it is not considered a national health emergency. Dr. Dianna Blau, the CDC's acting parasitic diseases branch chief, said there is no evidence the parasite has evolved to become more infectious. Thousands of cyclospora illnesses are reported annually in the U.S., and it is unclear how unusual this year will be. However, current CDC national data shows the case total is four times higher than at the same point last year, though the data lags behind state reports.
Bagdasarian noted that Michigan's aggressiveness in investigating and reporting cases may be “part of the reason why this looks like a Michigan problem.”
Prevention and Recommendations
Officials advise people with diarrhea lasting more than a few days to see a health provider and discuss possible cyclospora infection. To prevent infection, avoid potentially contaminated food or water. Wash fresh produce thoroughly before eating, but note that cyclospora can stick to foods, so washing may not eliminate all risk.
Michigan officials recommend consumers purchase whole heads of lettuce rather than prewashed, bagged lettuce or salad mixes, and remove the outer two to three leaves before washing under running water. Cooking vegetables when possible is also advised.
