What is cyclospora? Diarrhoea symptoms, foods linked to US outbreak

Jeanne Marrazzo Estimates Thousands of Uncounted Cyclosporiasis Cases

The true scale of the crisis may be significantly higher than official tallies. According to Jeanne Marrazzo, CEO of the Infectious Diseases Society of America, the actual number of cases is likely at least double the CDC’s count. Marrazzo notes that most people do not seek medical care for diarrhea, and even when they do, laboratories do not routinely test for the parasite. “Many people aren’t going to declare themselves and get counted,” she stated. Some reports indicate there are nearly 7,000 potential cases, with more than 3,300 in Michigan alone as of Tuesday, where state officials have identified tainted lettuce as the likely culprit.

Surveillance and Diagnostic Challenges

CDC Downgrades FoodNet Surveillance for Cyclospora and Other Pathogens

Cyclospora is a microscopic parasite that causes an intestinal illness called cyclosporiasis. It is notoriously difficult to detect in a clinical setting. Because many routine stool tests do not include the parasite, a clinician must specifically consider it before a laboratory will look for it. A patient may suffer from two weeks of relentless watery diarrhea—sometimes 20 episodes a day—and leave a clinic without a diagnosis if a provider does not order an assay that specifically includes Cyclospora cayetanensis.

The ability to track these infections has also been impacted by federal policy changes. On July 1, 2025, the CDC downgraded FoodNet, an active surveillance network it has operated with the FDA, the USDA, and 10 state health departments since 1995. This move made the tracking of Cyclospora optional at its sites, along with five other pathogens including Listeria, Campylobacter, Shigella, Vibrio, and Yersinia. Only Salmonella and E. coli remain as mandatory pathogens for surveillance.

Transmission and Investigation

FDA Conducts Traceback Investigations on Fresh Produce

The U.S. Food and Drug Administration (FDA) is currently conducting traceback investigations on multiple fresh produce items, though no specific food has been confirmed as the source of the current outbreak. Cyclospora is primarily transmitted through the fecal-oral route, usually after a person consumes contaminated food or water. It does not typically spread directly from person to person. Food becomes contaminated when an infected person with poor hand hygiene handles it.

The parasite is a recurring concern during warmer months when fresh produce consumption increases. Health officials warn that symptoms may not appear immediately, as the infection can take days to manifest, making it difficult for patients to identify the specific source of their illness.

Symptoms and Clinical Care

The hallmark symptom of the illness is watery, sometimes explosive, diarrhea. Unlike many other gastrointestinal illnesses, Cyclospora is not typically associated with significant vomiting or fever. Other symptoms include bloating, nausea, and excessive gas. Dr. Tyler Evans, founder and CEO of the Wellness Equity Alliance, highlighted the specific risks of the infection in an interview with Newsweek: The most dangerous feature of cyclosporiasis is the duration. Untreated, cyclosporiasis can persist for weeks, and the diarrhea is often watery and relapsing. The danger is cumulative: dehydration, electrolyte loss, and weight loss over time.

Healthcare providers typically treat the infection with the antibiotic trimethoprim/sulfamethoxazole (TMP/SMX). For patients with a sulfa drug allergy, providers may prescribe ciprofloxacin or nitazoxanide. Supportive care, including hydration with water, electrolyte sports drinks, or, in severe cases, IV fluids, is often recommended alongside antidiarrheal medications like loperamide or diphenoxylate-atropine to prevent dehydration.

With proper diagnosis and treatment, most patients feel better within one to two weeks, although occasional bouts of diarrhea may persist for a time. Because of the risk of severe dehydration and other complications, individuals experiencing persistent gastrointestinal symptoms should consult a qualified healthcare professional to determine if testing and antibiotics are necessary.

Find more reporting in our Health section.