Health officials in Illinois are still investigating four recent cases of a rare parasite that causes diarrhea and flu-like symptoms.
Illinois Department of Public Health spokeswoman Sabrina Miller says federal health officials haven't yet identified a food source for the Illinois cases of cyclosporiasis.
Iowa and Nebraska have linked some cases in their states to pre-packaged salad mix.
The stomach bug has sickened 372 people in 15 states.
None of the Illinois cases required hospitalization.
The illness is not generally contagious and can be treated with antibiotics.
Health experts recommend washing hands before handling food and thoroughly washing all fresh produce.