At least 285 people in 11 states have been sickened by a parasitic infection commonly linked to fresh produce, but the exact cause of the outbreak has yet to be pinpointed, the U.S. Centers for Disease Control and Prevention said Thursday.

Most of the cyclospora infections have been clustered in the Midwest, with 138 cases reported in Iowa and 70 in neighboring Nebraska. The remainder are in Texas, Georgia, Wisconsin, Connecticut, Illinois, Kansas, Minnesota, New Jersey and Ohio.

The cause of the illness has not yet been identified, but the parasite is most commonly found in fresh produce, including fruits, vegetables and herbs, grown in tropical and subtropical regions, according to Dr. Barbara Herwaldt, a medical epidemiologist at the CDC.

"Because no food item has been implicated to date, we're not yet sure the cases in the various states are related," she said. "Though it's quite likely that the cases in the Midwest might be."

At least 18 people in three states have required hospitalization from the cyclospora parasite, which causes an intestinal infection called cyclosporiasis.

Cyclosporiasis is caused by ingesting food or water containing a one-celled parasite that is too small to be detected without a microscope. Symptoms include watery diarrhea, vomiting and body aches.

The symptoms usually hit within several days of eating contaminated food. If not treated, the illness may last from a few days to a month or longer, and patients have been known to relapse, the CDC said.

The first cases were reported in Iowa in late June, with the majority of the illnesses logged in early July.

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