(NEXSTAR) – The Centers for Disease Control and Prevention are warning consumers after a salmonella outbreak impacting people in six states has been linked to raw cookie dough from Papa Murphy’s.

In a notice posted Tuesday, the CDC reports at least 18 people contracted salmonella between late February and early May. Half of them reported eating Papa Murphy’s take-and-bake raw cookie dough before becoming sick.

Papa Murphy’s has issued a “Stop Sell order” for its take-and-bake Chocolate Chip Cookie Dough and S’mores Bars, which have portions of the chocolate chip cookie dough, the company said Monday.

The CDC and Papa Murphy’s warn that if you have any of the take-and-bake doughs mentioned above, you should discard it immediately.

Six people sickened in the outbreak live in Washington, while four were Oregon residents, CDC investigators say. Four additional cases were reported in Idaho, two in Utah, and one each in California and Missouri.

Patients ranged in age from 14 years old to 68. Of those who became ill, two were hospitalized.

Federal investigators say the true number of people that became sick as a result of this salmonella outbreak may be much higher because many people are able to recover without medical treatment and are never tested.

At least two people who contracted salmonella did not eat at Papa Murphy’s, according to the CDC, which notes its investigators are trying to determine which ingredient caused those cases.

Earlier this year, the CDC linked another salmonella outbreak to Gold Medal flour after multiple people reportedly became sick after eating raw cookie dough. The agency advises against eating raw cookie dough since most contain raw flour or unpasteurized eggs that carry germs like salmonella and E.coli.

What is salmonella?

It’s caused by the salmonella bacteria, which the CDC estimates causes 1.35 million infections, 26,500 hospitalizations, and 420 in the U.S. yearly.

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.

Other recent salmonella outbreaks have been linked to alfalfa sprouts, raw salmon, and bearded dragons – all CDC investigations into these outbreaks have been closed.