Notes from the Field: An Outbreak of Shiga Toxin–Producing Escherichia coli O121 Infections Associated with Flour — Canada, 2016–2017
On December 29, 2016, PulseNet Canada identified a cluster of six Escherichia coli non-O157 isolates with a matching pulsed-field gel electrophoresis (PFGE) pattern combination that was new to the PulseNet Canada database. The patients resided in three geographically distinct provinces. In January 2017, the Public Health Agency of Canada (PHAC) initiated an investigation with local, provincial, and federal partners to investigate the source of the outbreak.
A case was defined as isolation of E. coli non-O157 with the outbreak PFGE pattern or closely related by whole genome sequencing (WGS) in a Canadian resident or visitor with onset of symptoms of gastroenteritis on or after November 1, 2016. Patients’ illness onset dates ranged from November 2016 to April 2017 (Figure). As of May 23, 2017, a total of 29 cases were identified in six provinces (Alberta, British Columbia, Newfoundland and Labrador, Ontario, Quebec, and Saskatchewan). One additional case was identified in a U.S. resident who traveled to Canada during the exposure period. Patients’ ages ranged from 2–79 years (median = 23.5 years) and 50% were female. Eight patients were hospitalized, and one developed hemolytic uremic syndrome. Clinical isolates were typed as E. coli O121:H19 (one case was typed as E. coli O121:H undetermined) with Shiga toxin 2–producing genes by in silico toxin testing and had closely related PFGE patterns and WGS.
Initial investigation into the source of the outbreak did not identify any clear hypotheses; common exposures were ground beef, sausage style deli-meats, pizza, and pork, but the data did not converge on any specific products. Patients were reinterviewed by PHAC using an open-ended approach. Knowledge of a recent E. coli O121 flour-associated outbreak prompted interviewers to ask about baking and exposure to raw flour or dough (1). Patients were also asked if any food items of interest, including flour, were available for testing.