The Centers for Disease Control and Prevention said in an investigation notice published on Thursday that flour is believed to be the source of a multi-state salmonella outbreak that has sickened about a dozen people and hospitalized three.

It’s not clear what brand the outbreak could be related to, the agency said.

“State and local public health officials are interviewing people about the foods they ate in the week before they got sick. Of the 7 people interviewed, 6 (86%) reported eating raw dough or batter,” the CDC said. “Flour was the only common ingredient in the raw dough or batter people reported eating. Investigators are working to identify a specific brand of raw flour that is linked to illnesses.” 

Most flour is raw, meaning that it hasn’t been treated to kill germs that cause food poisoning. When flour is mixed into dough or batter and baked, salmonella germs are killed in the process, but people can get sick from the raw dough or batter.

No deaths have been linked to the outbreak at this time, the CDC said. Sick people have been identified in California, Illinois, Iowa, Minnesota, Missouri, Nebraska, New York, Ohio, Oregon, Tennessee and Virginia. The first illness was reported in early December 2022, the agency said. 

“The true number of sick people in this outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses,” the agency said in the investigation’s details

To avoid illness, the agency recommends not eating raw dough or batter, because even small amounts can cause illness. Baked goods should also be prepared according to instructions, to make sure germs are fully killed. This warning is in effect even when there is not an outbreak, the CDC said. 

Heat-treated flour, which is not raw, can be used as a substitute in recipes for homemade playdough or in raw goods. 

Symptoms of salmonella include diarrhea, fever and stomach cramps. The symptoms can start within six hours of starting the bacteria, but can begin as much as six days later. Most people recover without treatment in four to seven days, the CDC reports. Older people, children and those with weakened immune system may need to be hospitalized if they experience a severe illness. The CDC recommends calling a healthcare provider if you experience a diarrhea for more than three days, a high fever, signs of dehydration or extreme vomiting.