PERRYVILLE, Mo. (AP) – A southeast Missouri county is investigating a salmonella outbreak that has sickened 34 people.

The cause hasn’t been determined. Perry County Health Department communicable disease coordinator Sheila Hahs says the agency began receiving worrying numbers of positive salmonella diagnoses from the Perry County Memorial Hospital on Aug. 7. The agency typically received just three to five confirmed salmonella cases each year.

County health officials are working with the U.S. Department of Health and Human Services to investigate possible causes. The typical cause is contaminated food.

The Centers for Disease Control and Prevention most people infected with salmonella develop a fever, cramps or diarrhea within 12 to 72 hours of being exposed to the bacteria.