WASHINGTON » The Food and Drug Administration says an outbreak of stomach illnesses in Iowa and Nebraska is linked to salad mix served at Olive Garden and Red Lobster restaurants in those states and supplied by a Mexican farm.

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

“It is not yet clear whether the cases reported from other states are all part of the same outbreak,” the agency said in a statement. “The investigation of increased cases of cyclosporiasis in other states continues.”

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

The agency said its investigation has not implicated packaged salad sold in grocery stores.

The salad mix may be out of the commercial food chain as the most recent known illness in those two states was in Nebraska a month ago. The typical shelf life for a salad mix is up to 14 days.

There have been more recent illnesses in other states. According to the Centers for Disease Control and Prevention, the most recent illness was July 23.