Cyclospora cayetanensis is a coccidian protozoan that causes cyclosporiasis, a severe gastroenteric disease, especially for immunocompromised patients, children, and the elderly. The parasite is considered as an emerging organism and a major contributor of gastroenteritis worldwide.

Currently, nineteen Cyclospora species have been reported to be causative agents of disease in various animal species [5] and only one species, C. cayetanensis, is known to be associated with syndromes of acute and chronic diarrhea in humans.

As of Tuesday, the Centers for Disease Control and Prevention said it had received reports of 1,645 confirmed cases of cyclosporiasis, the gastrointestinal affliction caused by the parasite Cyclospora.

But the true number of infections is likely much higher, because that figure only represents cases reported by states directly to the CDC. There is also a lag between symptom onset and reporting, and many people recover from the illness without medical treatment. Michigan alone reported 3,309 cyclosporiasis cases as of Tuesday.

Only 249 cases had been reported nationally at this time last year.

People can become infected when they drink water or eat raw food, usually raw produce, that is carrying the parasite. Food picks up the parasite most often through water supplies that are infected with human feces.

Cyclosporiasis is not transmitted via person-to-person contact.

C. cayetanensis is a parasite that must live inside a human host for part of its life cycle, as well as living outside the host during an environmental phase. Although there are many species of Cyclospora, only C. cayetanensis has been known to cause illness in humans, an infection called cyclosporiasis. A person can become infected after ingesting food or water contaminated with the parasite. Infected people (including those who are asymptomatic or show no symptoms of illness) can shed the parasite in their feces. Without good hygiene practices, among other protections, this can result in the contamination of food, water and the environment and lead to the infection of other people.

Although chlorine and other antimicrobial chemical treatments are effective at reducing harmful populations of bacteria and viruses, they are not considered effective on C. cayetanensis. In countries/regions where cyclosporiasis is endemic, microfiltration, ozone, or UV treatments may be necessary to effectively decrease populations of C. cayetanensis in irrigation waters.

Although clinical testing for the parasite in human feces has been available since the 1970s, FDA recently improved the method for the detection of this parasite on some fresh fruits and vegetables. Traditional microbial testing (such as for fecal indicators like generic E. coli or fecal coliforms) will not identify the presence of C. cayetanensis but may help identify poor water quality, which may also be an indicator of human fecal contamination.

A popular California company has been linked to the growing cyclosporiasis outbreak, according to a new report.

The Washington Post, citing two individuals familiar with the investigation, first reported Thursday that federal investigators have identified iceberg lettuce supplied by Taylor Farms to Taco Bell restaurants as a possible source of contamination.

CNN and others are also reporting the ongoing investigation into Taylor Farms as a source of the cyclosporiasis outbreak.

Taylor Farms, founded and headquartered in Salinas, California, describes itself as the "leading global producer of salads and healthy fresh foods." In addition to the Golden State, the company has production facilities across the U.S., along with Mexico, Canada and Europe.

Some better-known foodborne pathogens, such as Salmonella or E. coli, cause symptoms within a few days of consumption. But cyclosporiasis symptoms can take up to two weeks to appear — too long for people to easily recall exactly what they ate, and where. ‌By that time, ⁠fresh produce items such as tainted lettuce may already be out of stores or restaurants.

The tiny parasite that causes cyclosporiasis cannot be traced using the most advanced testing methods in which scientists grow pathogens in their labs and sequence the full genome of the organism. This produces a genetic fingerprint that can be matched with contaminated food sources.

Because this is a parasite and not a bacterium, cyclospora cannot be grown or cultivated in labs — a process that increases the amount of genetic material used to confirm its presence.

The US Food and Drug ⁠Administration (FDA) said on Sunday that laboratory experts re-checked lettuce sample results from Taylor Farms in an ⁠investigation into an ⁠outbreak of the cyclospora parasite and concluded the finding should be considered a false positive.

As of Sunday, there were ⁠no confirmed positive sample results for cyclospora, the FDA added. The FDA on Saturday had said that a ⁠sample of shredded iceberg lettuce supplied by Taylor Farms tested positive for the parasitic illness that has ‌sickened thousands of ‌people in the US.

"To be clear, at this moment, FDA has not identified a single positive product test result for cyclospora," the company said. Taylor Fresh Foods added that it had completed a voluntary recall of iceberg lettuce ‌from central Mexico out of an abundance of caution based on the initial information given.

Taylor Farms has also said that the FDA apologized. The company had earlier confirmed that ⁠the product was not part of its current recall, according to the FDA.

Health officials said they did not offer Taylor Farms an official apology.

"To clarify, this false-positive lab sample DOES NOT change the basis for FDA's ongoing outbreak investigation or the overwhelming epidemiological data supporting the current voluntary recall by Taylor Farms," it said.

Health and Human Services Secretary Robert F. Kennedy Jr. told ABC News on Tuesday that the multi-state cyclosporiasis outbreak in the U.S. is "under control."

"We do have the outbreak under control," Kennedy said. "We have an extensive forensics, epidemiological forensics, and we've identified the source of the outbreak. We and the companies that are involved have implemented a recall."

In a letter sent to Kennedy last week, Ossoff said the CDC's Foodborne Diseases Active Surveillance Network, known as FoodNet, no longer requires reporting the parasite that causes cyclosporiasis.

The CDC ended mandatory reporting last year. Beginning July 1, 2025, reporting became optional for all pathogens except Salmonella and Shiga toxin-producing E. coli, according to the CDC.

Kennedy told ABC News criticisms of the federal response are "invalid" saying they're "still doing surveillance in this space."

"We had no cuts in our surveillance program. We did cuts in the FoodNet program, but they were for redundant surveillance," Kennedy said. "And all this space will tell you that we're still doing forensics. We're still doing surveillance in all this space."

For those with cyclosporiasis, Talaat says there is an effective treatment: The antibiotic trimethoprim/sulfamethoxazole, brand name Bactrim or Septra, taken for seven to 10 days. While Cyclospora is a parasite, not bacteria, the antibiotic is effective against it.

Talaat says many won't even realize they had cyclosporiasis. "For most healthy adults, it's often a self-limited infection; it will go away by itself," she says.