The Iowa Department of Public Health says there are now 60 confirmed of the rare food-borne illness cyclosporiasis, up from 45 cases reported Friday.
Neighboring Nebraska reported 35 cases as of Friday.
A Nebraska Department of Health and Human Services spokeswoman did not immediately respond to a message Saturday asking if more cases had been confirmed in Nebraska.
The illness is most commonly contracted by eating food or drinking water contaminated with human feces containing the cyclospora parasite.
Iowa typically has just one or two cases a year, usually travelers.
Officials believe fresh vegetables may be the culprit, but the investigation continues.
Consumers should wash fruits and vegetables to reduce the risk of the illness, which causes diarrhea that lasts an average of 57 days.