The United States is experiencing a major Cyclospora outbreak that researchers describe as the largest in national history. Since May 1, officials have confirmed 1,645 cases across 45 states, with more than 5,100 additional infections under review. Michigan leads with the highest count. Over 100 people have been hospitalized, though no fatalities have occurred.
Cyclospora cayetanensis is a single-celled parasite that invades cells lining the intestines. It multiplies inside these cells, damaging tissue and impairing water and nutrient absorption. Symptoms, primarily watery diarrhea, usually appear after one week or longer. Infection occurs only after ingesting food or water contaminated by human feces containing mature oocysts.
Oocysts require one to two weeks in warm conditions between 22 °C and 32 °C to become infectious, which explains the summer timing of outbreaks. The standard medication is the antibiotic combination trimethoprim-sulfamethoxazole, which deprives the parasite of a needed vitamin.
Health authorities have not yet identified every source, but Michigan officials suspect lettuce or salad greens. The FDA has linked one cluster to shredded iceberg lettuce supplied to Taco Bell restaurants in five states. Investigators collect stool samples from symptomatic individuals, confirm the parasite, and interview patients about recent meals.
Prevention relies on thorough hand washing with soap and water, since alcohol sanitizers are ineffective. Vinegar rinsing outperforms water alone. Heating produce to 158 °F or above kills the organism. Past outbreaks have been tied to leafy greens, fresh herbs, berries, and certain raw vegetables. The typical season extends through late August, so case numbers may continue rising.
