An outbreak of cyclosporiasis—an illness caused by the cyclospora parasite—is making people sick across the United States, with health officials reporting hundreds of cases in more than a dozen states.

Cyclospora is a one-celled parasite that infects people through contaminated food or water, and outbreaks have often been tied to fresh produce and seasonal conditions. Investigations are ongoing into the specific source(s) of contamination, but public health guidance focuses on reducing exposure while authorities work to identify where the parasite entered the food supply.

Officials say the parasite is commonly associated with produce such as raspberries, snow peas, mesclun lettuce, basil, and cilantro—items that can be harder to clean thoroughly. Health officials also emphasize that cyclospora illness is not typically spread from person to person; instead, infection occurs after ingesting contaminated stool-linked contamination that reaches food or water.

Health departments are advising people to follow food-safety habits aimed at preventing foodborne illness, including washing produce thoroughly under running water before eating, cutting, or cooking; scrubbing firm produce with a clean brush; cutting away bruised or damaged areas; and refrigerating cut or prepared produce promptly.