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Flour outbreak was first time non-O157 STEC infections identified in Canada

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By Joe Whitworth+



The outbreak of E. coli O121 in flour was the first time non-O157 Shiga toxin–producing E. coli (STEC) infections had been identified nationally in Canada.

It was also the first Canadian outbreak linked to flour, said researchers.

“Because of the recent emergence of E. coli outbreaks linked to flour, public health professionals should consider flour as a possible source in E. coli outbreaks and communicate the risk associated with exposure to flour, raw batter, and dough in public health messaging,” they added.

Flour made by Ardent Mills

The Public Health Agency of Canada (PHAC) said the outbreak appears to be over and the Canadian Food Inspection Agency (CFIA) is verifying unsafe food has been removed from store shelves.

Ardent Mills recalled various brands of flour made in October 2016 at the Saskatoon, Saskatchewan plant. The firm is an independent joint venture of ConAgra Foods, Cargill and CHS.

“Consumer food safety is of paramount importance to Ardent Mills, and our mills adhere to stringent and mandated food safety protocols to ensure pathogenic bacteria are not introduced during the milling process at any of our operations,” said Kent Juliot, VP of research, quality and technical services.

A total of 29 cases were identified in Alberta, British Columbia, Newfoundland and Labrador, Ontario, Quebec, and Saskatchewan. One additional case was a US resident who travelled to Canada during the exposure period.

Patients’ ages ranged from two to 79 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 E. coli O121:H undetermined) with Shiga toxin 2–producing genes by in silico toxin testing and had closely related PFGE patterns and WGS.

Open-ended approach and past outbreak

In late December last year, PulseNet Canada identified a cluster of six E. coli non-O157 isolates with a matching pulsed-field gel electrophoresis (PFGE) pattern new to the PulseNet Canada database.

Patients’ illness onset dates ranged from November 2016 to April 2017.

Initial investigation into the source did not identify any clear hypotheses; common exposures were ground beef, sausage style deli-meats, pizza and pork but data did not reveal any specific products.

Patients were re-interviewed 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.

Last year in the US, 63 people were infected with outbreak strains of STEC O121 or STEC O26 from 24 states. Flour produced at a General Mills facility in Kansas City, Missouri was the likely source.

In March this year, E. coli O121 with the outbreak PFGE pattern was isolated from Robin Hood brand open flour from a patient’s home and a closed sample at retail of the same brand and production date.

The clinical and flour isolates grouped together, with only 0-6 whole genome multilocus sequence typing allele differences. As a result, a product recall was made.

Based on possible connections to the recalled lot of flour, market sampling within certain periods was started. The investigation led to additional recalls and many secondary products .

Of 22 patients who were asked about flour in the seven days before illness onset; 16 reported that the implicated brand of flour was used or probably used in the home.

Eleven of the sixteen ate or probably ate raw dough during the exposure period.

Source: MMWR Morb Mortal Wkly Rep 2017; 66: 705–706

Notes from the Field: An Outbreak of Shiga Toxin–Producing Escherichia coli O121 Infections Associated with Flour - Canada, 2016–2017

Authors: Morton V, Cheng JM, Sharma D, Kearney A.

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