More than 250 people have been sickened, mostly in the Midwest, by a rare parasite that may have contaminated fresh produce shipped across state lines, said federal health officials, who've stepped in to help coordinate the growing outbreak.

At least 118 cases of cyclospora infection have been reported in Iowa, another 65 in Texas and 68 in Nebraska, state officials said. Four more cases have been reported in Wisconsin and one each in Illinois and Kansas. At least eight people have been hospitalized, the Centers for Disease Control and Prevention reported.

So far, there's no clear source for the illnesses, reported since mid-June. But officials suggest fresh vegetables may be the source, based on interviews with people who got sick.

Cyclospora is a microscopic protozoan parasite excreted in human stool. Protozoa are tiny, one-celled animals that breathe, move and reproduce.

Symptoms of infection can include weeks or months of watery diarrhea -- but the infection is treatable with common antibiotics. People who have unexplained stomach troubles are urged to seek medical help and ask whether a test for cyclospora infection might be necessary.

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