Michigan health officials are investigating an unusually large outbreak of cyclosporiasis that had reached 1,251 reported cases by July 9, including 44 hospitalizations, according to the Michigan Department of Health and Human Services.
The outbreak is concentrated in southeastern Michigan, where local and state health departments are trying to interview patients and trace what they ate or drank before becoming sick. Officials have not identified the source, or sources, of contamination.
The count has moved fast. MDHHS reported that the outbreak began with two cases on June 22. By July 4, the state had 572 cases. On July 8, officials received 239 reports, the highest one-day count so far. Another 159 case reports came in on July 9.
Cases are also rising in nearby northwestern Ohio. The Associated Press reported that counties in that region have logged more than 500 cases, including 306 in Lucas County as of Wednesday.
What the parasite does
The illness is caused by Cyclospora cayetanensis, a single-celled parasite spread through fecal contamination. In the United States, infections are most often linked to contaminated produce, though contaminated drinking water can also spread it.
The mechanics matter here. Health experts say person-to-person spread is unlikely because the parasite does not become infectious immediately after it is passed in stool. It usually needs one to two weeks in the environment before it can infect another person. That delay points investigators toward shared food or water exposures rather than a quick chain of household transmission.
After infection, symptoms usually begin about a week later, though MDHHS says onset can range from two days to more than two weeks. The main symptom is watery diarrhea that can come frequently and forcefully. Nausea, fatigue, cramps and bloating can also occur. Without treatment, diarrhea may last a month or longer, and dehydration is a key concern.
Health officials say people who develop diarrhea should contact a health care provider to determine whether they have cyclosporiasis. The illness can be treated with trimethoprim-sulfamethoxazole, an antimicrobial combination sold as Bactrim.
A bad summer marker for Michigan
Nationally, the United States has recorded about 2,000 to 5,000 cyclospora cases a year in recent years, with infections peaking in the warmer months, especially June and July. Michigan’s current outbreak is far outside its usual pattern. MDHHS has said the state’s annual totals in past years have generally been around 50 cases, making the July count roughly 25 times that level.
MDHHS is urging caution with produce that has been associated with past outbreaks. The agency recommends buying whole heads of lettuce instead of bagged lettuce, removing the outer two or three leaves, and washing the inner leaves well. For green onions, officials advise trimming them, removing outer layers and washing thoroughly.
The department also says cilantro, basil and snow peas should be washed under running water. Raspberries are trickier because the parasite can cling to them and be difficult to remove. MDHHS says cooking is the safest option, while frozen berries may reduce risk but do not remove it.
This story draws on original reporting from Ars Technica.
