The first reported cases occurred in Iowa, which has been hardest hit with 143 people falling ill so far. The first cases came in late June, with more infections reported through July.
Other states reporting large numbers of infections are Nebraska, with 78 cases, and Texas, with 101 cases.
It takes about a week for people who are infected to become sick.
Dr. Thomas Frieden, CDC director, urged people who have suffered from diarrhea longer than a couple of days to be tested for cyclospora. Antibiotics can be used to treat severe cases of infection.
Earlier outbreaks of cyclospora have been traced back to fruits and vegetables imported from tropical regions like Latin America and Southeast Asia, where the parasite is common, Parise and Hirsch said.
"Our food supply system is large, complex and centralized. We get foods from all over the world, and they are packaged together and sent very, very quickly," Hirsch said. "I look at large outbreaks like this, and it makes me wonder if more locally grown foods would be safer."
People who want to avoid infection should thoroughly wash all their fruits and vegetables, Hirsch said. They also should wash cooking surfaces and utensils with hot, soapy water.
"For the most part, it's a miserable nuisance, but the concern I have as a doctor is for patients whose immune systems are weakened [and] have a real hard time with this infection," Hirsch said. He urged extra caution for people undergoing cancer treatment, recovering from an organ transplant or dealing with HIV infection.