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Updated: Feb 18, 2026
Characterization of a Pathogenic Escherichia coli Strain Derived from Oreochromis spp. Farms Using Whole-Genome Sequencing
Published on: December 23, 2022
Shiga Toxin-Producing E. coli Infections Associated with Flour
Samuel J Crowe1, Lyndsay Bottichio1, Lauren N Shade1
1From the Centers for Disease Control and Prevention (S.J.C., L.B., L.W., A.B., M.N.S., D.W., E.T., M.E.W., K.P.N.), and IHRC (L.B., D.W.), Atlanta; Food and Drug Administration, College Park, MD (L.N.S., B.M.W., J.B., S.V.); Colorado Department of Public Health and Environment, Denver (N.C.); Washington State Department of Health, Shoreline (B.M.), and Food and Drug Administration, Bothell (J.W., L.A.N.) - both in Washington; Michigan Department of Health and Human Services, Lansing (K.D.A., D.D.); Oklahoma State Department of Health, Oklahoma City (J.S.); and Virginia Department of Health, Richmond (K.A., J.R.).
Background:
In 2016, a multijurisdictional team investigated an outbreak of Shiga toxin-producing Escherichia coli (STEC) serogroup O121 and O26 infections linked to contaminated flour from a large domestic producer.
Methods:
A case was defined as infection with an outbreak strain in which illness onset was between December 21, 2015, and September 5, 2016. To identify exposures associated with the outbreak, outbreak cases were compared with non-STEC enteric illness cases, matched according to age group, sex, and state of residence. Products suspected to be related to the outbreak were collected for STEC testing, and a common point of contamination was sought. Whole-genome sequencing was performed on isolates from clinical and food samples.
Results:
A total of 56 cases were identified in 24 states. Univariable exact conditional logistic-regression models of 22 matched sets showed that infection was significantly associated with the use of one brand of flour (odds ratio, 21.04; 95% confidence interval [CI], 4.69 to 94.37) and with tasting unbaked homemade dough or batter (odds ratio, 36.02; 95% CI, 4.63 to 280.17). Laboratory testing isolated the outbreak strains from flour samples, and whole-genome sequencing revealed that the isolates from clinical and food samples were closely related to one another genetically. Trace-back investigation identified a common flour-production facility.
Conclusions:
This investigation implicated raw flour as the source of an outbreak of STEC infections. Although it is a low-moisture food, raw flour can be a vehicle for foodborne pathogens.
