The Centers for Disease Control and Prevention (CDC) has recently investigated whether consuming raw flour was the cause of an E. coli infection that affected more than fifty people.
We are well-aware that consuming certain raw or undercooked foods can make an individual sick. For example, raw chicken can cause Salmonella or Campylobacter infections and raw beef can cause an E. coli infection. Avoiding raw eggs is arguably the most difficult guideline to adhere to – how many people can really say that they’ve never eaten raw cookie dough or cake batter? However, raw eggs are a common reservoir for Salmonella. The New England Journal of Medicine recently reported another potential reservoir for foodborne pathogens in homemade goods – flour.
Bacteria Can Lay Dormant in Uncooked Flour for Months
Flour is a raw, minimally processed ingredient that should be cooked before consumption. Due to its low water content, flour does not typically support bacterial growth. However, disease-causing bacteria can survive the flour drying process and lay dormant for months in storage.
STEC Outbreak in 2016
People can acquire the shiga toxin-producing E. coli infection (STEC) from consuming contaminated food. This E. coli infection causes fever, abdominal pain, diarrhea, and in severe cases, even kidney failure. In 2016, an outbreak of STEC infections in the United States prompted an investigation led by the Centers for Disease Control and Prevention (CDC). The investigation included 56 cases across 24 states. Over one-quarter of these patients were hospitalized, and one adolescent female patient suffered kidney failure. Fortunately, there were no deaths in this outbreak.
Strong Associations Between STEC Infections and Baking
The CDC led a long and challenging investigation. The initial molecular analysis revealed that the infectious bacteria isolated from all patients originated from a common source. A series of interviews and questionnaires indicated that there were strong associations between STEC infections and baking, using the same brand of flour, and tasting uncooked dough or batter. They used non-STEC infections (i.e. Salmonella) during the same period as a control to rule out common exposures.
Although most patients had discarded their flour packaging, the CDC found the packaging for two bags. This flour was manufactured in the same plant within one day of each other. Genetic analysis revealed that STEC strains isolated from the flour were the same as STEC strains isolated from patients. The source of contamination was not identified at the production facility suggesting it was the wheat in the field that was contaminated. Many farmers use cattle manure as a fertilizer, which can act as a reservoir for foodborne pathogens.
Flour: An Unexpected Culprit
This investigation was resource-intensive and lengthy because flour was an unexpected culprit. In fact, most routine state and national foodborne disease questionnaires do not even include flour. The authors suggest that the CDC should revise standard procedures for investigating foodborne diseases to include flour as a potential outbreak source. Unfortunately, we now have another reason to resist raw cookie dough.
Written by Mallory Wiggans
Reference: Crowe, Samuel J., et al. “Shiga Toxin–Producing E. coli Infections Associated with Flour.” New England Journal of Medicine 377.21 (2017): 2036-2043.