CDC Investigates E. coli Infection Linked to Raw Flour Consumption

Understanding the Risks of Raw Foods

The Centers for Disease Control and Prevention (CDC) has recently conducted an investigation into the potential link between raw flour consumption and an E. coli infection that impacted over fifty individuals. It is widely recognized that consuming certain raw or undercooked foods can lead to illness. For instance, raw chicken can result in Salmonella or Campylobacter infections, while raw beef is associated with E. coli infections. One of the more challenging guidelines to follow involves avoiding raw eggs, as many individuals have likely indulged in raw cookie dough or cake batter. Raw eggs are known to frequently harbor Salmonella.

Flour as a Potential Reservoir for Pathogens

The New England Journal of Medicine has highlighted another potential source of foodborne pathogens in homemade foods—flour. Flour is a minimally processed raw ingredient that should be cooked before consumption. Due to its low moisture content, flour typically does not support bacterial growth; however, harmful bacteria can survive the drying process and remain dormant for extended periods during storage.

Historical Context: The 2016 STEC Outbreak

Individuals can contract shiga toxin-producing E. coli (STEC) infections through the consumption of contaminated food. Such infections can lead to symptoms including fever, abdominal pain, diarrhea, and in severe cases, kidney failure. In 2016, the CDC investigated an outbreak of STEC infections across the United States, which involved 56 cases across 24 states. More than a quarter of those affected required hospitalization, and one adolescent female experienced kidney failure, although there were no fatalities reported during this outbreak.

Investigation Findings and Associations

The CDC’s investigation was thorough and challenging. Initial molecular analyses confirmed that the bacteria isolated from patients originated from a common source. Interviews and questionnaires suggested strong associations between STEC infections and activities related to baking, specifically the use of a particular flour brand and the tasting of uncooked dough or batter. The investigation employed non-STEC infections, such as Salmonella, as a control to eliminate common exposure factors.

Although most patients had discarded their flour packaging, the CDC managed to identify the packaging for two bags of flour. These bags were produced in the same facility within one day of each other. Genetic analyses revealed that the STEC strains from the flour matched those found in the patients. The contamination source at the production facility was not identified, indicating that the wheat itself may have been contaminated, potentially due to the use of cattle manure as fertilizer by farmers, which can harbor foodborne pathogens.

Reevaluating Foodborne Disease Investigations

This investigation was notably resource-intensive and lengthy, primarily because flour was an unexpected source of contamination. In fact, routine state and national foodborne disease questionnaires typically do not include flour as a potential risk factor. The authors of the study recommend that the CDC revise its standard procedures for investigating foodborne diseases to include flour as a possible source of outbreaks. Unfortunately, this incident further emphasizes the need to resist the allure of raw cookie dough.

References

Crowe, Samuel J., et al. “Shiga Toxin–Producing E. coli Infections Associated with Flour.” New England Journal of Medicine 377.21 (2017): 2036-2043.