Last week we reported on a new study that implicated raw chocolate chip cookie dough as the cause of a large outbreak of E. coli in 2009. Researchers said it was the first time an outbreak of food poisoning caused by the dangerous Shiga toxin-producing E. coli has been traced to store-bought, ready-to-bake cookie dough. The outbreak, between March and July 2009, sickened at least 80 people across 30 states, 35 of whom had to be hospitalized.

Now new data suggests the culprit in the sickenings was not contaminated raw eggs, as many suspected, but instead the flour used in the mixtures, according to researcher Dr. Karen Neil, a medical epidemiologist with the Centers for Disease Control and Prevention.

“Out of all the ingredients, raw flour is the only raw agricultural product that was in the cookie dough,” Dr. Neil told the New York Times. “It didn't undergo any specific processing to kill pathogens, so we feel that's the most likely suspect for what may have introduced contamination into the cookie dough. We couldn't prove it conclusively, but that's what we suspect.”

The eggs used in the contaminated cookie dough were pasteurized, a process that kills pathogens. The molasses, sugar, baking soda and margarine used in the dough also underwent “pathogen kill steps” during processing that made them unlikely to be sources of the contamination, and the chocolate chips used in the dough revealed no evidence of E. coli, the researchers said.

According to the NYT, “One study that looked at commercial wheat flour samples found almost 13 percent contaminated with E. coli. The investigators also pointed out that wheat flour can also be contaminated with Salmonella, and that flour-based mixes have previously been implicated in outbreaks of food-borne illness.”

Does this mean that if you're a messy homemade cookie baker, you could potentially end up with E. coli all over your kitchen, hands, face, body and dogs? Sucks.

Follow Samantha Bonar @samanthabonar.

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