If you had never heard of cyclospora until this summer, you’re not alone. A gastrointestinal parasite that infected 2,700 people in the U.S. in all of 2025 has reportedly infected at least 7,000 people by July 14 of this year, according to the Centers for Disease Control and Prevention (CDC), with numbers consistently ticking upward. Cases of cyclosporiasis have been recorded in 34 states so far, though the epicenter appears to be in Michigan, where over 5,000 suspected cases have been reported.

Jeffrey Griffiths, a professor in the Department of Public Health and Community Medicine at Tufts University School of Medicine, and Giovanni Widmer, a professor in the Department of Infectious Disease and Global Health at Cummings School of Veterinary Medicine at Tufts University explain where cyclospora comes from, the common signs and symptoms of cyclosporiasis, as well as means of prevention and treatment. 

Cyclospora are microscopic parasites that, when ingested via contaminated foods, multiply inside the cells of the gastrointestinal tract, impairing its function, and causing excessive and persistent diarrhea. Cyclosporiasis is typically contracted by consuming fresh produce like berries, lettuce, and herbs that have been contaminated with the cyclospora parasite. The illness is generally not transmitted directly from person to person, because the form that is excreted by a sick person must develop outside the body for one to two weeks before becoming infectious.

The CDC tracks cases of cyclosporiasis in the U.S. from May 1 through August 31 each year, the typical cyclospora season when the combination of warmer weather and imported seasonal produce arrive.

“This parasite is an endemic problem for other countries like Guatemala and Honduras that might have more prevalent issues with public sanitation,” Widmer says.

Cyclosporiasis in the U.S. pops up when infected human fecal matter has made its way into the food supply abroad, which is then imported to the U.S. and consumed by people who buy the product. The recent outbreak has been officially attributed to lettuce grown in Mexico and distributed by a California-based company to Taco Bell locations in at least five states.

Griffiths was among the first experts called in response to a cyclospora outbreak at a wedding in the Boston area in the mid-1990s, which was eventually sourced to fresh raspberries served on a dessert. Raspberries, with their deep nooks and crannies, are typically served fresh and are difficult to wash, making it a ripe host for cyclospora. Other fresh, uncooked, and difficult-to-wash foods (such as strawberries) can also be likely sources.

The primary symptom of cyclosporiasis is excessive and prolonged diarrhea, but unlike many other kinds of food-borne illness, it does not cause prominent nausea and vomiting, nor is it typically accompanied by a fever. Also, unlike diseases with similar symptoms like norovirus and food poisoning, cyclosporiasis doesn’t clear up within 24 hours, but can linger for weeks or even months. Though 9% of reported CDC cases have been hospitalized to date, no one has died this year from a cyclospora infection.

The amount of time between consumption of contaminated food and symptoms of cyclosporiasis can range from four to 14 days, which experts expect is correlated with the dose — the more that’s consumed, the sooner symptoms begin. Widmer says that kind of information relies on qualitative epidemiological data of patients reporting that symptoms started after they ate something several weeks ago that they think might have been the source.

“This complicates the process of identifying a food that might have been the vector for transmission,” Griffiths says.

If symptoms persist for 48 hours, Griffiths recommends seeing a doctor and getting tested for cyclosporiasis. The condition can be treated with an antibiotic (trimethoprim-sulfa), which was discovered largely by accident when attempting to treat patients in Nepal in the 1970s and 80s when the disease was first discovered. Symptoms should clear up soon after treatment starts, but Griffiths reassures that even if a patient can’t take the medication, it will likely resolve on its own, even if it takes several weeks.

For now, Griffiths recommends washing produce under clean water as thoroughly as possible, but not avoiding fresh produce altogether, as it is necessary for a healthy diet. However, he concedes common sense precautions might be considered for people living in Michigan and other areas with high case numbers. He also recommends extra caution for those with heart disease, kidney disease, or compromised immune systems.

Several factors are contributing to this year’s severe outbreak, the source of which was believed to be iceberg lettuce that was sold at stores and restaurants in multiple states, but the U.S. Food and Drug Administration later said that may have been a false positive, and the investigation is ongoing.

First, the potentially long incubation period can make finding the source more difficult as patients are asked to remember everything they ate and who they ate with for the past several weeks.

Second, this outbreak isn’t hyperlocalized, and investigating cases across the country connected through a complex supply chain is no easy task. 

And third, recent changes to the CDC, which is responsible for investigating such outbreaks, have made things more difficult. Last summer, budget cuts at the CDC left it with fewer epidemiologists to conduct these investigations. In addition to investigative epidemiology, suspected foods are also tested in a laboratory for potential contamination, which while expensive and laborious, adds certainty when it confirms the presence of the parasite in the suspected food. 

The CDC also made reporting cyclospora infections optional where it used to be mandatory. Broadly, Griffiths says that means there will be fewer reported cases of cyclosporiasis. In any situation, fewer reports means fewer leads and fewer opportunities to find the source.

“While it’s of course upsetting and disruptive to people’s lives who get infected,” Griffiths says, “the bigger concern is that the scope and timeline of the outbreak is a very obvious symptom of how the public health protections we've gotten used to have been weakened over time.”

(Newswise/HG)