Michigan Cyclosporiasis Outbreak Grows to 992 Cases as Health Officials Seek Source

Nearly 1,000 people in Michigan have been diagnosed with cyclosporiasis, a parasitic infection that can cause weeks of watery diarrhea, and the outbreak has grown to 992 cases with about 40 hospitalizations as of Wednesday.

The Michigan Department of Health and Human Services first announced the outbreak last week with more than 170 cases since June 22, and investigators still have not identified the source of the cyclospora infections.

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Across the Michigan border, Lucas County, Ohio reported 306 cases as of Wednesday, while northwest Ohio has seen more than 500 cases.

Dr. Natasha Bagdasarian, Michigan’s chief medical executive, told The Associated Press that "there is clearly a linked outbreak happening right now," as health officials continue to investigate similar illnesses in 28 other states.

The U.S. Centers for Disease Control and Prevention described cyclosporiasis as causing watery diarrhea "with frequent and sometimes explosive bowel movements," and said no deaths have been reported in the current outbreak.

Investigators have yet to determine a common cause for multiple clusters of cyclosporiasis, and USA TODAY reported that the size and nature of the outbreak have the CDC and Food and Drug Administration looking to pinpoint its origins.

USA TODAY explained that whole genome sequencing, which is used to trace other foodborne illnesses, is not routinely used for Cyclospora because the parasite generally does not give investigators enough clean parasite DNA to work with.

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A CDC study cited by USA TODAY found that roughly 20% of submitted Cyclospora specimens failed genotyping, and the article said technicians cannot grow the parasite in labs, making it hard to draw evidence from contaminated produce.

Food safety attorney Bill Marler told USA TODAY that the longer incubation period makes it harder for people to remember what they ate, saying, "The longer (incubation) is, the harder it is for people to remember what they ate."

The CDC also reported on its website that as of July 1, "there is currently no evidence of a single, multistate Cyclospora outbreak linking all cases," while investigations to identify potential sources are ongoing.

Michigan health officials urged people to prevent infection by avoiding prewashed bagged lettuce or salad mixes and instead buying a whole head of lettuce, throwing away the outer two or three layers, and thoroughly washing the inner leaves under running water.

The Detroit Free Press reported that Michigan’s health and agricultural leaders had not identified a common source as of July 7, even as the number of cases in Michigan swelled to 700, and it said public health investigators continued to interview people who had been sick.

Dr. Natasha Bagdasarian said health officials’ current leading hypothesis is that the outbreak is likely related to produce, and The Detroit News reported that cases had been identified in at least 43 Michigan counties with the largest number, 215, in Monroe.

The Detroit Free Press also said the safest option is to cook leafy greens, cilantro, basil, green onions, snow peas and raspberries after carefully washing them, and it noted that heating food to 158 degrees or higher kills the parasite.

In Illinois, NBC 5 Chicago reported that Illinois health officials said 150 cases of the parasitic infection were detected as of Wednesday, with 68 domestically acquired and 16 pending investigation, while the Illinois Department of Public Health said it had not identified a single source.