(AP) — The Food and Drug Administration says an outbreak of stomach illnesses in Iowa and Nebraska is linked to restaurant salad mix supplied by a Mexican farm.

The outbreak of cyclospora infections has sickened more than 400 people in 16 states. The agency says it is working to determine whether the salad mix is the source of illnesses in the other 14 states.

The FDA traced illnesses from four restaurants to Taylor Farms de Mexico, a processor of food service salads.

The agency did not identify the restaurants where the salad mix was served. The agency said its investigation has not implicated packaged salad sold in grocery stores.