Uncooked flour likely causes more E. coli illnesses and outbreaks than health officials once presumed, according to a newly published study in the New England Journal of Medicine.
“Our data show that although it is a low-moisture food, raw flour can be a vehicle for foodborne pathogens,” the researchers said in the Nov. 23 report Shiga Toxin-Producing E. coli Infections Associated with Flour.
The researchers noted that certain behaviors in the kitchen such as licking a spoon used to stir cake batter or eating raw cookie dough have long been discouraged because of the risk of illnesses associated with the consumption of raw eggs. But now that researchers have discovered that E. coli bacteria can survive in raw flour, it appears likely that flour causes more instances of foodborne illness than previously thought.
According to researchers, health authorities investigating a 2016 outbreak of E. coli illness found that in three instances of pediatric infection, restaurant staff had given children raw dough to play with in restaurants while they waited for their food. In other instances, contaminated flour was used to make play-dough at home.
“Flour is a raw, minimally processed product intended to be mixed with other ingredients and cooked before consumption,” the researchers noted in the study. “It is a low-water-content ingredient and typically does not support bacterial growth. Nevertheless, pathogenic microorganisms on the wheat or other ingredients in flour can survive the drying process and remain viable in flour for months in a desiccated state.”
The researchers said that while flour has been a suspected vehicle for outbreaks of Shiga toxin-producing Escherichia coli (STEC) infections since 2009, when a multistate outbreak of foodborne disease was linked to prepackaged cookie dough, it was never definitively identified as a likely source.
The 2016 outbreak of E. coli linked to raw flour compelled the study. That outbreak sickened at least 63 people in 24 states and led to 17 hospitalizations. The Centers for Disease Control and Prevention (CDC) eventually traced the outbreak to flour made by General Mills. That discovery led to an immediate recall of 10 million pounds of flour. The recall later expanded to encompass cake and pancake mixes.
Researchers said that raw flour escaped attention as a culprit in E. coli illnesses until recently, mainly because the time between infection and signs of illness can take up to 10 days. Also, “Some case patients did not report exposure to flour in the week before illness onset … Interviews often occur weeks to months after the illness, which makes it difficult for the patient to recall exposures accurately,” the researchers said.
One takeaway from the study for everyday consumers is that E. coli infections from raw flour are likely more common than previously believed – something to keep in mind next time you use flour in the kitchen.