A six-state outbreak of Salmonella linked to raw cookie dough from Papa Murphy’s restaurants has been declared over by the Centers for Disease Control and Prevention.

The CDC reports that 26 people were confirmed as part of the outbreak, with four of them requiring hospitalization. No deaths were reported. The sick people lived in California, Idaho, Missouri, Oregon, Washington and Utah.

Traceback work by the CDC and the Food and Drug Administration found that most of the outbreak patients reported eating raw cookie dough from the restaurants.

Labels from implicated products provided by FDA.

“Of the 22 people interviewed, 17 reported eating food from Papa Murphy’s. Fifteen people ate Papa Murphy’s raw chocolate chip cookie dough or raw S’mores bars dough, and one person ate baked cookies made with Papa Murphy’s chocolate chip cookie dough,” according to the CDC’s outbreak update.

“The true number of sick people in this outbreak was likely much higher than the number reported, and the outbreak may not have been limited to the states with known illnesses. This is because many people recover without medical care and are not tested for Salmonella.”

Specific testing is required to diagnose Salmonella infection, which mimics other illnesses.

Illnesses started on dates ranging from February 24 to May 28, according to the CDC. On May 23, Papa Murphy’s temporarily stopped selling their raw chocolate chip cookie dough and raw S’mores bars dough in response to this outbreak. As of July 13, Papa Murphy’s has not restarted sales of cookie dough and is reviewing their dessert labels to make it clear to customers that their products are not intended to be eaten raw.

Public health investigators used the PulseNet system to identify illnesses that were part of this outbreak. CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses. DNA fingerprinting is performed on bacteria using a method called whole genome sequencing (WGS). WGS showed that bacteria from sick people’s samples are closely related genetically. This suggests that people in this outbreak got sick from the same food.

Public health officials always advise people to not eat raw dough or batter because it contains raw ingredients such as flour, which can harbor bacteria such as Salmonella and E. Coli.

The CDC offers the following tips for the safe use of raw dough, batter and flour:

• Never eat any raw dough that is supposed to be cooked or baked. 
• Always wash hands and clean and sanitize work surfaces and utensils thoroughly after contact with raw dough or batter. 
• Keep raw food or dough separate from other foods while preparing them to prevent any possible contamination from spreading.