A mysterious outbreak of cyclosporiasis has now been reported across more than 30 US states, with health officials still unable to identify what is driving the surge in cases. The parasite behind the illness has proven notoriously difficult to trace, a challenge experts say has been compounded by cuts to federal health surveillance programmes.
Cyclosporiasis is caused by Cyclospora cayetanensis, a single-celled parasite that infects the bowel and typically causes watery diarrhoea, with bowel movements that can become frequent and, at times, explosive, according to a CDC fact page. The illness spreads through contact with Cyclospora-contaminated faecal matter, most commonly via fresh produce tainted through agricultural irrigation, and tends to appear in outbreaks during late spring and summer. The parasite requires around one to two weeks in the environment before becoming infectious, which the CDC says makes direct person-to-person transmission “unlikely.”
Case numbers climbing fast
According to the CDC, the outbreak has now been confirmed in 34 states, with nearly 7,000 cases reported overall. In a separate update issued on Friday, the CDC put the number of confirmed cases at more than 800, with state health departments separately reporting figures running into the hundreds or thousands. Michigan has been hit hardest, with more than 3,300 cases according to the CDC, while the Michigan Department of Health and Human Services (MDHHS) has more recently put the state’s total at 992 cases in its own latest update. Federal data shows this year’s Michigan case count running at roughly four times the level recorded at the same point last year. No deaths have been linked to the outbreak so far.
The outbreak has also spread beyond Michigan’s borders. According to the Associated Press, Lucas County in Ohio has documented 306 cases as of Wednesday, with surrounding counties in the northwest of the state reporting more than 500 cases combined, suggesting the cluster first identified in Michigan’s south-eastern counties has now crossed into neighbouring Ohio.
Why the source remains elusive
Dr Teena Chopra, an infectious-disease professor at Wayne State University in Detroit, said identifying the source of the outbreak remains the central obstacle to bringing it under control. “All we need to do is identify the source, but it’s taking a long time,” she said. She noted that because cyclosporiasis does not spread between humans, outbreaks should in theory become easier to contain once the source of contamination is found.
Part of the difficulty lies in the delay between exposure and illness, which can take up to two weeks. Jodie Guest, senior vice chair of epidemiology at Emory University’s Rollins School of Public Health, said most foodborne illnesses cause symptoms within hours, making it relatively easy to trace the responsible food. With cyclosporiasis, however, that lag means infected people often struggle to recall what they ate over the preceding fortnight, and not everyone who falls ill is tested, further limiting the data available to investigators.
Steven Manderach, executive director of the Association of Food and Drug Officials, described the scale of the challenge. “This isn’t like detecting a needle in a haystack. It’s like detecting a microscopic portion of a needle in a haystack,” he said. He explained that testing food for the parasite is unusually labour-intensive, requiring large quantities of a suspect product to be washed, with the resulting runoff reduced and tested for the organism’s presence. “You’d have to have truckloads of lettuce to get to that point,” said Manderach, who previously worked on cyclosporiasis outbreaks as a food-safety official in Iowa. Given the scale of this year’s outbreak, public health experts believe there are likely multiple points of contamination across the food supply, adding a further layer of complexity to the investigation.
Cuts to federal surveillance add to the strain
Some experts say budget and staffing cuts within the US Department of Health and Human Services (HHS) have further complicated efforts to trace the outbreak. The cuts, introduced by Health Secretary Robert F Kennedy Jr as part of billionaire Elon Musk’s Department of Government Efficiency (Doge) cost-cutting drive, led the federal government to scale back its Foodborne Diseases Active Surveillance Network (FoodNet), which had previously monitored pathogens including cyclospora, salmonella and listeria. FoodNet reduced its monitoring to just two pathogens last year. In a memo to the state of Connecticut cited by NBC News, the CDC acknowledged that “funding has not kept pace” with what the programme required.
Guest, who previously worked at FoodNet, said the loss of that infrastructure has left investigators with far less information than they once had. “When we see an outbreak or a cluster or something, we don’t have the data we normally expect to go back to use to help us, and this is one of those consequences,” she said. “You’re starting in the dark.”
HHS said the CDC continues to work with 3,000 health departments nationwide and is still gathering cyclospora data through surveillance systems beyond FoodNet, adding that funding for foodborne disease programmes has “remained stable”. In Colorado, which has recorded around 90 cases this year, roughly consistent with previous years, a state health department spokesperson, Hope Shuler, said the state has had less federal funding and fewer staff to monitor cases as a result of the changes. “While our colleagues at the CDC are working hard to support state partners, we have had to adapt to federal changes,” she said, adding that Colorado has continued testing, monitoring and reporting data to the CDC regardless.
Manderach struck a more measured note on the overall federal response, saying agencies responsible for food safety are largely functioning to previous standards. “While yes, I do think there were challenges early on, most of those seem to have resolved,” he said. David Weber, professor of medicine, paediatrics and epidemiology at the University of North Carolina at Chapel Hill, pointed out that other serious global health emergencies, including the Ebola outbreak in the Democratic Republic of Congo, have also placed strain on available resources. Nancy Glick of the National Consumers League said the funding shortfalls have effectively shifted more of the burden onto individual states. “States are doing that now, but they don’t have the resources that the CDC had,” she said.
Tracing the outbreak one interview at a time
With no single source identified, epidemiologists are now working through a labour-intensive process of interviewing everyone who has tested positive about what they ate in the one to two weeks before falling ill, in an effort to identify a common product, restaurant or supplier. Weber said the method itself is straightforward but resource-heavy. “It is pretty straightforward, but it takes a lot of person power to do it,” he said, a burden that falls hardest on smaller local health departments with limited staff.
What’s known about the illness itself
While rarely fatal, cyclosporiasis can cause prolonged bouts of diarrhoea and resulting dehydration, which pose more serious risks for children, the elderly and immunocompromised patients. The illness can be treated effectively with antibiotics, but if left untreated can persist for anywhere from a few days to more than a month. The CDC also notes that symptoms have a tendency to wax and wane, sometimes returning one or more times even after appearing to improve.
Where the risk is highest, and how to reduce it
According to CDC surveillance data, the outbreak spans the Eastern Seaboard, the South from Arizona to Florida, the Midwest, and has even been reported in Alaska. Health officials have advised cooking fresh produce where possible and avoiding prewashed plastic tubs or bags of greens and salad mixes. Past US outbreaks of cyclosporiasis have been linked to various types of imported fresh produce, including raspberries, basil, snow peas and mesclun lettuce, with the CDC noting that no commercially frozen or canned produce has ever been implicated.
In Michigan, MDHHS has issued an advisory urging restaurants and the public to thoroughly wash, and preferably cook, high-risk fresh produce, including green onions and fresh cilantro, recommending that at-risk food be heated to at least 158°F (70°C) to kill the parasite. Raspberries have been singled out as particularly difficult to clean due to the texture of their surface, with MDHHS advising that they either be cooked or bought frozen, while cautioning that “freezing may reduce but does not guarantee elimination of the parasite.”
Guest acknowledged the difficulty this places on ordinary consumers trying to protect themselves. “At the moment, the list of things that you need to be concerned about is unfortunately quite long, making it feel really hard to control,” she said. Officials say their investigation remains ongoing as they continue working to establish how the parasite entered the food supply and why the outbreak has spread so widely.
