In a news release issued Monday, health officials in Michigan identified a possible source of an outbreak of cyclosporiasis, an illness resulting from infection with the parasite cyclospora, which is transmitted through food and water contaminated with feces.
“Current results point to lettuce or salad greens as a potential source for this outbreak,” officials said via the release, though they cautioned that the source was not yet definitive, and that other food items could not be ruled out. They also did not specify a grower or supplier.
As of Monday evening, health officials in Michigan had reported 2,640 cases and 44 hospitalizations — a 69 percent increase in cases from those reported on Friday, and the highest number of cases ever reported in Michigan in a single year. The state typically records only 40 to 50 cases per year.
While Michigan is currently reporting the most cyclospora infections in the country, the Centers for Disease Control and Prevention has said that many other states — including New York, Ohio, Illinois, Indiana and Kentucky — are reporting higher than typical numbers of cases of cyclospora. The C.D.C.’s latest figures include at least 843 confirmed illnesses across 31 states, and 86 hospitalizations.
The C.D.C. figures are most likely an undercount, health experts say, as it takes time for states to report cases to the agency and for the agency to confirm them. The New York Times has independently confirmed at least 4,800 cases of cyclospora so far this year. Since 2016, the C.D.C. has reported an average of about 2,800 cases per year nationwide.
This year is “on track to be the biggest year on record” for cyclosporiasis in the United States, said Caitlin Rivers, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health who is tracking the cases.
Lettuce and salad mixes, as well as other types of fresh produce including raspberries, basil, cilantro, fruit mixes, snow peas and snap peas, have been implicated in previous cyclospora outbreaks in the United States. A 2020 outbreak linked to Fresh Express bagged salads containing iceberg lettuce, red cabbage and carrots — the largest in recent history in the United States, according to the C.D.C. — sickened 701 people across 14 states. The C.D.C. also linked a 2022 Florida outbreak to bagged salads, including Caesar salad kits containing romaine lettuce.
Given the previous link with lettuce and salad greens and the early signs that they may be causing illness in Michigan, health officials there issued specific guidance for preparing the greens. Instead of buying bagged or pre-mixed salad kits, they recommended using whole heads of lettuce, discarding the outer two to three layers of leaves and then washing the inner leaves thoroughly under running water.
They also recommended washing other fresh produce under running water. Washing will not completely remove the parasite, but it can reduce its numbers and the risk of illness. Health officials have also recommended peeling produce with removable skin, and cooking produce to at least 158 degrees, a temperature that kills the parasite.
Cyclospora infections cause watery diarrhea, with frequent, sometimes “explosive” bowel movements. Other symptoms can include loss of appetite, cramping, bloating, nausea and fatigue. Although serious complications are rare, the symptoms can linger for months if not treated.
Those with symptoms should see a health care provider for testing and treatment of the illness, the C.D.C. said on Friday. Cyclosporiasis can be treated with antibiotics.
