Cases of a foodborne intestinal infection have more than doubled in North Carolina over the past week, according to state health officials.

More than 300 North Carolinians have contracted cyclosporiasis since May, and 13 people have been hospitalized. About 70% of the reported cases originated in Wake County.

Cyclosporiasis is caused by a microscopic parasite that can contaminate food or water. Symptoms can include diarrhea, stomach cramps, nausea, fatigue and weight loss.

So far, investigators have not identified the primary source of the infections.

Thirty-four states have confirmed cases. North Carolina’s numbers are among the highest nationwide, according to the latest data from the Centers for Disease Control and Prevention.

Because the parasite is often linked to raw produce, health officials are urging consumers to thoroughly rinse fruits, vegetables and fresh herbs before eating them.