Cyclospora Cayetanensis

Cyclosporiasis is an intestinal illness caused by the unicellular, coccidian parasite Cyclospora cayetanensis. Transmission occurs by ingestion of food or water contaminated with human feces. Humans are the only known hosts of this parasite.

Cyclosporiasis is most common in tropical and subtropical regions of the world such as Mexico, the Caribbean and Central America. In the United States, cases of cyclosporiasis have been reported among travelers to such areas. Cyclosporiasis became a nationally notifiable disease in the US in January 1999 after several large multi-state outbreaks. The United States typically records between 3,000 and 4,000 cases per year. 

In June 2026, a large outbreak of Cyclosporiasis occurred in southeast Michigan and northwest Ohio. While these states appear to be the epicenter of Cyclospora activity, 31 states have already reported more than 3,500 cases and 86 hospitalizations. The actual number is almost certainly higher because most people experiencing diarrhea do not seek care from a physician and physicians often do not order tests for Cyclospora. 

This outbreak is expanding quickly because the federal government still has not identified the contaminated food. The reasons include the lack of centralized coordination by the federal government, our siloed health systems, and insufficient capacity at state and local health departments.As of July 1, 2025, FoodNet, the main food-borne illness surveillance arm of the CDC made tracking Cyclospora optional. Consequently, CDC has not provided updated national data regarding Cyclospora outbreaks. 

Cyclospora oocysts are not killed by the routine chemical disinfection or sanitizing methods used by food processors. The Food Safety Modernization Act Produce Safety Rule does not require growers or food processors to test for this parasite. 

Food-borne outbreaks occur in the United States almost every year from May through September. Produce usually becomes contaminated at the farm or irrigation source and is then distributed to stores. The most commonly contaminated fresh produce includes basil, cilantro, lettuce, raspberries, snow peas and prepackaged salad mix. Washing produce reduces the risk of infestation, but does not eliminate it. Cooking does kill oocysts, so cooked vegetables are a safer choice during outbreaks. Cyclospora does not spread from person to person.

Cyclospora inhabits the small intestine. Cyclospora infection can be asymptomatic or symptomatic. Asymptomatic infection is most common in endemic regions. Among persons who develop symptomatic Cyclospora infection, the incubation period averages 1 week (range: 2 to >14 days). Symptoms include explosive watery diarrhea, loss of appetite, weight loss, abdominal cramping, bloating, nausea, fatigue, vomiting, and low-grade fever. Most people recover in one to two weeks. However, the very young, elderly, and immunocompromised individuals may have remitting and relapsing symptoms for 10 to 12 weeks. The recommended treatment for cyclosporiasis is trimethoprim-sulfamethoxazole (Bactrim). 

Routine ova and parasite examinations of stool typically do not detect Cyclospora oocysts. They are detected with a modified acid-fast stain or a modified safranin stain. The latter stain has better sensitivity. Oocysts appear clear to pink and refractile. If the ova and parasite exam fails to detect oocysts and Cyclospora infection is strongly suspected, molecular testing can be performed. The FilmArray Gastrointestinal Pathogen Panel utilizes nucleic acid amplification to detect multiple viral, bacterial and parasitic pathogens including Cyclospora. 

Stool specimen is required for testing. Reference value is negative. 

References

Casillas SM, Hall RL, Herwaldt BL. Cyclosporiasis Surveillance — United States, 2011–2015. MMWR Surveill Summ 2019;68(No. SS-3):1–16. 

Visvesvara GS et al: Uniform staining of Cyclospora oocysts in fecal smears by a modified safranin technique with microwave heating. J Clin Microbiol 1997;35:730-733).

Goetzman J, Carter A, Oliveira A, Ingram LA. Outbreak of Cyclosporiasis Among Patrons of a Mexican-Style Restaurant — Limestone County, Alabama, May–June 2023. MMWR Morb Mortal Wkly Rep 2025;74:217–221.