Why we don’t know what food is spreading the parasite sickening thousands
More than 2,000 Americans fell ill this summer with a microscopic parasite that contaminates fresh produce and can cause diarrhea for days, public health officials said, creating an unusually large outbreak that may paradoxically give researchers the best chance of identifying the source.
Cyclospora is one of the most difficult foodborne pathogens to trace to its source. There is a delay between people consuming the disease-causing parasite and symptoms appearing, making it difficult for those infected to remember what they ate to pinpoint the problem. Health officials are alarmed by the rapidly rising number of cases and say they are likely being undercounted because some people recovered without medical attention and were not tested.
Authorities have not yet identified a specific grower, supplier or type of product responsible for the latest outbreak that has left more than 80 people hospitalized. But this season’s unusually high number of illnesses, now reported in more than 30 states, means more patients and more information to help identify shared foods, shopping habits and restaurant visits among patients to help identify the source.
“Given the number of cases we’re seeing across the country, I would hope and suspect that we would have a pretty good idea of what the food vehicles are that could be causing these diseases,” said Frank Yiannas, former Food and Drug Administration commissioner for food policy and response.
Janet Hamilton, executive director of the Council of State and Territorial Epidemiologists, which represents state disease detectives investigating outbreaks, said of so many cases: “We know there has to be a source to which people were exposed; a contaminated food or product. This does not spread from person to person.”
“We also know that the source is still there, given how quickly cases are increasing,” Hamilton added.
Cases of cyclosporiasis are reported year-round in the United States, but are most common in spring and summer; The season generally runs from May 1 to August 31. Past outbreaks in the United States have been linked to a variety of fresh produce, including basil, raspberries, salad mixes, cilantro and peas.
The national rise is largely due to a few states reporting above-average case counts, while others say total cases are near seasonal norms.
Michigan and Ohio report the largest numbers. Disease toll rises to more than 1,500 in Michigan; That’s roughly 30 times what the state has recorded for a year. Michigan is now issuing daily updates as researchers search for the source. At least 44 people were hospitalized, mostly due to dehydration, officials said.
Last month, Michigan officials received more than 170 reports of the disease over nine days in the southeastern region along the Ohio border. The state sent an alert to health care providers noting the “unusual number of cases” officials had identified in less than a week.
“There’s more awareness, so more people are watching for symptoms, more people are being tested,” said Natasha Bagdasarian, Michigan’s chief medical officer. “Cyclospora is not something that is routinely tested for when someone has GI symptoms, and I think we are catching more cases as a result.”
At least 28 people were hospitalized in Ohio, state health officials said. As of July 9, Ohio is reporting nearly 400 cases, most of which state and county officials say have occurred since June 20.
“This is a serious illness that can cause dehydration and require people to seek emergency medical care, and it needs to be taken seriously,” said Bruce Vanderhoff, Ohio’s health director.
What is cyclosporiasis and what are its symptoms?
Cyclosporiasis is a disease caused by the cyclospora parasite, which infects the small intestine and lives inside a human host for part of its life cycle. It is usually not life-threatening and usually causes watery diarrhea with frequent and sometimes “explosive” bowel movements, according to the Centers for Disease Control and Prevention. People can become infected by consuming food or water that contains the parasite. It is not transmitted from person to person. Not everyone who is infected experiences symptoms.
People may be at risk of infection when living or traveling in tropical or subtropical areas of the world where the parasite occurs regularly in an area or region.
But Bagdasaryan said that unlike other gastrointestinal diseases where vomiting is the predominant symptom, this infection is predominantly characterized by diarrhea, especially watery diarrhea. Other symptoms may include abdominal cramps, some nausea, and perhaps some low-grade fever.
Other gastrointestinal diseases may resolve within a few days, but symptoms of cyclosporiasis can last for weeks if left untreated.
“So people may feel a little better, then feel very bad again, and this can last for several weeks,” Bagdasarian said. he said.
A delay in diagnosis can also delay seeking medical care, he said.
The disease is usually treated with the antibiotic trimethoprim-sulfamethoxazole, also known as Bactrim, Septra, or Cotrim.
What do experts recommend to reduce the risk?
Health officials say there are ways to reduce the risk until the culprit or culprits behind the latest wave of illness are identified.
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Wash your hands with soap and water before and after handling or preparing raw fruits and vegetables.
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Wash all fruits and vegetables thoroughly under running water before eating, cutting or cooking.
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Scrub hard fruits and vegetables, such as melons and cucumbers, with a clean produce brush.
Michigan has made more specific recommendations for establishments in the southeast region, where most cases have been reported. They note that most foods are safest when cooked.
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Lettuce/leafy greens: Purchase whole heads of lettuce (instead of pre-washed, bagged lettuce or salad mixes), discarding the outer 2-3 layers of leaves and washing the inner leaves under running water.
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coriander, basil: Separate the leaves and wash them thoroughly under running water.
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Scallion: Cut off the root end and remove the outer layer, wash thoroughly under running water.
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Raspberry: It makes cleaning uneven surfaces particularly difficult; The parasite can hide in small crevices. Consider frozen raspberries as an alternative (freezing may reduce the parasite but does not guarantee eradication).
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Snow peas: Wash under running water and scrub the surface.
Why this epidemic is so hard to understand
It is difficult to understand the full scope of how many people have become ill. Case numbers on the CDC’s website lag state numbers by several weeks because some states are reporting probable and confirmed cases. Some states are delaying sending out information until case investigations are completed.
Dianna Blau, acting chief of the CDC’s parasitic diseases branch, said the data on the CDC’s website, which will now be updated every two weeks, mostly reflects confirmed cases. The agency’s latest numbers, as of July 9, show 843 cases have been reported in the U.S. in people who got sick after eating and did not report any travel in the 14 days before getting sick, the CDC said.
But the agency is aware of more than 1,500 additional cases in the U.S. that require further analysis to confirm whether people have become ill.
The CDC said many states have reported increases in cases in the past two weeks compared to the same period in 2025. The agency said it anticipates the number of cases will continue to increase.
It is difficult to trace the source of these outbreaks. The parasite has a long incubation period, which delays the appearance of symptoms and can make people sick for up to two weeks. Diagnosis also requires a special test, not one that doctors usually order when patients suffer from gastrointestinal diseases.
“Compared to other foodborne outbreaks, symptoms appear anywhere from two days to two weeks, where in some of the more common foodborne outbreaks, the time between exposure and illness is a day or two,” Blau said.
Labor-intensive studies must rely on patients recalling what they ate going back as far as two weeks. They need to remember what foods they bought (including specific brands), how they used their products, and which restaurants or fast-food chains they ate at. Michigan authorities are analyzing records of people’s purchases tracked through supermarket loyalty cards to help with their investigation.
Genetic analysis of the pathogen is also more difficult. For outbreaks caused by more common foodborne bacteria and viruses, scientists can obtain full genetic fingerprints to determine whether patients were infected by the same organism; This helps trace outbreaks to a common source.
Cyclospora’s genetic material is “much larger” and the genetic fingerprint captures only a fraction of the material, Blau said. “And if you have less information, of course it’s harder to see the whole picture.”
Tracking foodborne outbreaks is complicated because the U.S. food distribution system is so complex that a single supplier can provide different types of products to restaurants, fast food chains, and grocery stores.
“If there was contaminated material on the shelves a few weeks ago, it may have gone to various places,” Bagdasaryan said. he said. “So it’s less about finding one gun and more about potentially finding several. So all of that makes the investigation particularly challenging.”
Often, a particular meal time may not have been consumed alone but incorporated into a variety of foods, making it difficult for sick individuals to remember. Blau said that the cyclospora epidemic that sickened dozens of people last year was linked to parsley, which was a part of the salad.
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Graphics:
Locations where Cyclosporiasis outbreaks were reported in 2026
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