Nearly 1,000 people in Michigan have been diagnosed with a parasitic infection that can cause weeks of watery diarrhea, making it the largest cyclospora outbreak in state history and one of the largest in the country in years.
Michigan officials first announced the outbreak last week, when they were tracking more than 170 cases, all in the southeastern corner of the state, dating back to June 22. Michigan typically identifies only about 50 cyclospora cases each year. By Wednesday, according to CBS News, that number had grown to 992, with about 40 hospitalizations. No deaths have been reported.
Just across the state line, Lucas County, Ohio, reported 306 cases as of Wednesday, and northwest Ohio has seen more than 400 cases total. Investigations into similar illnesses are also underway in 28 other states. The Centers for Disease Control and Prevention has confirmed cases in 17 states from early May through June 16, including Illinois, Maryland, Massachusetts, New York, and Texas.
The source of the current outbreak has not been identified. "There is clearly a linked outbreak happening right now," Dr. Natasha Bagdasarian, Michigan's chief medical executive, told The Associated Press on Wednesday.
Cyclospora is a microscopic, spherical parasite. According to the CDC, the illness causes watery diarrhea "with frequent and sometimes explosive bowel movements." The illness, called cyclosporiasis, is not usually life-threatening. Outbreaks tend to occur most often in late spring and summer.
The parasite infects the bowels and spreads through feces. People have previously been infected by consuming fruits or vegetables exposed to feces-contaminated irrigation water. The Michigan Department of Health and Human Services says past outbreaks in the U.S. and Canada were linked to bagged salad mixes, fresh cilantro, fresh basil, raspberries, snow peas, and scallions.
Cyclospora is less common than other foodborne illnesses such as salmonella and E. coli. Few U.S. outbreaks were reported each year for a long time, but the number began rising about a decade ago, with a notable spike in 2018 and 2019. Experts attribute the increase to climate change and better detection.
Available data shows only a small number of documented outbreaks in the last 20 years have surpassed 1,000 cases. One of those was a 1997 outbreak tied to Guatemalan raspberries that sickened more than 1,000 people in the U.S. and Canada. Michigan's current outbreak is approaching that threshold, with investigators still working to identify the food source.