Cyclospora cayetanensis is a unicellular, microscopic parasite that can cause food- or water-related gastrointestinal illness. Cyclospora cannot be transmitted directly from one person to another through infected fecal matter; the parasite must complete part of its lifecycle outside of a host. Most cases of cyclosporiasis occur in underdeveloped tropical and subtropical regions of the world where the parasite is endemic.
In the United States, Cyclospora causes about 11,000 illnesses and 11 hospitalizations, but infestations of this parasite do not typically result in death. Due to the self-limiting nature of the pathogen (which causes some people to not seek medical care), difficulty in diagnosing it specifically, and other factors, the Centers for Disease Control and Prevention (CDC) estimates that there could be very broad ranges of infection, from 140 to 38,000 annual cases. In North America, outbreaks of cyclosporiasis in humans have been reported mostly from contaminated fresh food products, such as soft fruits (raspberries, blackberries, and strawberries), leafy vegetables (lettuce and mixed salad), and herbs (basil and cilantro). Soil is another possible infection source, particularly in areas with poor environmental sanitation.
Since Cyclospora infections tend to respond to the appropriate treatment, complications are more likely to occur in individuals who are not treated or not treated promptly. These can include disorders of malabsorption, reactive arthritis, cholecystitis (inflammation of the gallbladder), and, possibly, Guillain-Barré Syndrome.