U.S. — The Centers for Disease Control and Prevention reported on July 28 that 45 U.S. states had reported cases of cyclosporiasis. The agency identified the parasitic illness as part of a growing outbreak linked to contaminated produce, prompting federal and state health officials to expand their investigations beyond initial food sources.

Shredded lettuce from Taylor Farms in central Mexico has been linked to Cyclospora illnesses in a nine-state cluster. In response to the emerging data, Taylor Farms voluntarily recalled shredded lettuce on July 17. Public health authorities are investigating additional sources of the Cyclospora outbreak as case counts continue to rise across the country.

No deaths have been reported from the Cyclospora outbreak, though hundreds of those affected have been hospitalized. The North Carolina state health department identified parsley and cilantro as potential sources in that state's outbreak, indicating that multiple supply chains may be involved in the widespread transmission.

Cyclosporiasis is a parasitic illness caused by eating or drinking contaminated food or water. People become sickened by Cyclospora when they ingest oocysts from food or water contaminated with traces of human waste. Cyclospora parasites lie dormant in pods called oocysts on the surface of herbs, vegetables, or berries.

Once swallowed, Cyclospora oocysts travel down the esophagus to the stomach and then the intestines. "The [oocysts] respond to signals in the gut, like body temperature, probably bile, digestive enzymes. This causes the parasites to be released," said Vernon Carruthers, professor of microbiology and immunology at the University of Michigan Medical School.

Cyclospora parasites burrow into the lining of the small intestine and replicate inside intestinal cells. "These grow from just a few of the parasites we would take in, to millions of parasites replicating inside our intestinal cells," Carruthers said. During infection, some Cyclospora parasites differentiate into egg- and sperm-like forms that combine to form new oocysts.

"This is truly remarkable, given that the sperm must find the eggs inside infected cells that are blanketed by a mucus layer," Carruthers said. "[The parasite is] entering those host cells, replicating in those cells, producing its life cycle within those cells. And that process eventually destroys the cells," said Joel Barratt, molecular parasitologist and associate professor at Emory University School of Medicine.

Cyclospora infections reduce nutrient absorption and cause symptoms such as nausea and diarrhea. A single milliliter of diarrhea from an infected person can contain around a thousand Cyclospora oocysts. Cyclospora infections can last for weeks or months.

"When [the oocysts are] immediately shed, they're not infectious. They have to sit out there in the environment and mature," Barratt said. The time required for Cyclospora oocysts to become infectious in the environment is unclear but may range from days to weeks. Cyclospora can enter the food system through tainted dirt, irrigation water, or handling by contaminated hands.

Cyclospora oocysts can survive chlorine, sunlight, and cold temperatures. "It's much more complex than the typical viral stomach bug that you can pass in a day or two," said Bobbi Pritt, microbiologist at Mayo Clinic and director of its Clinical Parasitology Laboratory. A combination of antibiotics sold under the brand names Bactrim, Septra, or Cotrim can treat Cyclospora infections by stopping parasite replication.

Cyclosporiasis is not typically fatal. In regions where Cyclospora is endemic, younger people tend to get symptomatic infections while older people often do not, suggesting immunity develops after several exposures. Large Cyclospora outbreaks occurred in the U.S. in 2018 and 2019.

"But this year it's just going straight through the roof," Barratt said. "We're getting produce and other food materials from all around the world. Many of these are endemic countries where people don't have access to good sanitary facilities," Pritt said. Health officials recommend washing and cooking fresh vegetables to reduce the risk of Cyclospora infection.

The scale of the current outbreak, spanning 45 states, exceeds the geographic reach of previous clusters and involves multiple potential food vectors including lettuce, parsley, and cilantro. The investigation shows the complexity of tracking pathogens in a globalized food supply chain where produce from endemic regions enters the U.S. market. While the initial recall targeted a specific supplier, the identification of additional sources in states like North Carolina suggests that contamination may be widespread across different agricultural operations.

Why It Matters

The parasite's ability to survive chlorine, sunlight, and cold temperatures complicates standard food safety measures, while its requirement to mature in the environment for days or weeks before becoming infectious extends the window for contamination. Because infections can last for weeks or months and reduce nutrient absorption, the widespread presence across 45 states poses a prolonged health burden distinct from typical short-term stomach bugs. The complex life cycle, which involves replicating inside intestinal cells until they are destroyed, means even small amounts of contaminated produce can lead to severe, long-lasting illness.