The CDC reported 206 cases of cyclospora infections from May 1 to August 1, according to CNN, compared with 88 cases during the same period last year.
Cyclospora cayetanensis is an intestinal parasite transmitted through contaminated food or water and causes watery diarrhea.
Previous outbreaks in the U.S. were mostly foodborne. The CDC has yet to identify any specific food items linking this year's cases.
A CDC official told CNN that this year's case count is not abnormally high; rather, last year's was low. "We put out this notice because the more complete the case reporting we can get, the easier it will be to figure out why this is happening," she said.