(NEXSTAR) – A salmonella outbreak that has sickened people in 11 states is renewing a call from the Centers for Disease Control and Prevention: stop eating raw cookie dough.

The agency confirmed last week it has launched an investigation into the outbreak, noting 12 illnesses have been reported. Three individuals have required hospitalization.

“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 CDC warned. So far, these states have each reported one case of an individual being infected with the salmonella outbreak strain: California, Iowa, Minnesota, Missouri, Nebraska, New York, Ohio, Oregon, Tennessee, and Virginia. Illinois has reported two cases.

CDC investigators say illnesses were confirmed between early December 2022 and mid-February 2023. It takes up to a month to determine if someone who falls ill is part of an outbreak, the agency explains.

Of the seven people state and local public health officials were able to speak with, six said they ate raw dough or batter in the week before they became sick. The only common ingredient across all of the dough and batter was flour.

The CDC is now trying to determine the specific brand of flour responsible for the illnesses.

“Flour doesn’t look like raw food, but most flour is raw,” the agency explains. “This means it hasn’t been treated to kill germs that cause food poisoning.”

Those germs could include salmonella, which is killed when the flour is cooked or baked.

To avoid becoming ill, the CDC not only urges against eating raw doughs or batters but using heat-treated flour, washing surfaces and utensils that touched raw flour, and keeping raw flour separate from foods that won’t be cooked.

Salmonella infections are commonly associated with diarrhea, fever, and stomach cramps, according to the CDC. Symptoms can begin between six hours and six days after you’ve ingested the bacteria. Most people are able to recover without receiving treatment within four to seven days.

Illnesses may be more severe for young children, the elderly, and those with weakened immune systems. Some may require medical treatment or hospitalization, the CDC explains.

Infections can only be diagnosed with a laboratory test of a person’s stool, body tissue, or fluids.

Every year, salmonella causes roughly 1.35 million illnesses and 420 deaths. Other recent salmonella outbreaks have been linked to alfalfa sprouts, raw salmon, and bearded dragons – all CDC investigations into these outbreaks have been closed.

Eating raw dough or batter can also lead to E.coli infections, the CDC warns.