LOS ANGELES, May 1 (Xinhua) -- Investigators have identified flour as the source of the recent Salmonella outbreak that has infected at least 13 people in 12 states, the U.S. Centers for Disease Control and Prevention (CDC) said Monday.

Interviews with sick people and laboratory data showed that Gold Medal flour contaminated with Salmonella has made people sick, said the CDC.

Three of the infected have been hospitalized without any deaths recorded yet. But the actual number of sick people is likely to be higher than reported, and the outbreaks may not be limited to the states with known illnesses, it said. "This is because some people recover without medical care and are not tested for Salmonella."

Last week, General Mills, the company producing Gold Medal flour, recalled two-, five- and 10-pound bags of bleached and unbleached all-purpose Gold Medal flour that have a "better if used by date" of March 27 and Mar 28, 2024.

People infected with Salmonella usually experience diarrhea, fever, and stomach cramps. Symptoms usually start six hours to six days after swallowing the bacteria, said the CDC.

Most people recover without treatment after four to seven days. Some people -- especially children younger than five years, adults aged 65 and older, and people with weakened immune systems -- may experience more severe illnesses that require medical treatment or hospitalization, according to the CDC.