Cyclospora cayetanensis is a parasitic human pathogen that, when ingested, can cause an intestinal illness called cyclosporiasis, which has been increasing in incidence in the U.S. over the past decade.^1,2 While our understanding of this parasite has increased greatly in the past decade, there are still many unanswered questions surrounding this parasite and its recent emergence: How does it make people sick, how does it enter the U.S. food supply, and how are the U.S. Food and Drug Administration (FDA) and its investigative partners responding?

It is helpful to start with what we do know: C. cayetanensis infects the small intestine, causing watery diarrhea with frequent, sometimes explosive, bowel movements. Cyclosporiasis can be treated with trimethoprim-sulfamethoxazole, also known as co-trimoxazole. If not treated, illness may last from a few days to a month or longer. C. cayetanensis is transmitted when feces from an infected individual contaminates food or water; however, it is not transmitted directly from person to person because after being shed, the parasite needs time (estimated one to two weeks, at least) in the environment to become infective.^1,3,4 C. cayetanensis is endemic in subtropical and tropical areas worldwide, and people living or traveling in countries where cyclosporiasis is endemic may be at increased risk for infection.⁵ Due to exposure during their early years, some people from areas where cyclosporiasis is endemic may be infected and shed the parasite without symptoms.