June 24, 2022

MMWR Covers Canadian Flour E. coli O121 Outbreak

The CDC’s Morbidity and Mortality Weekly Report (MMWR) for the week of July 78, 2017 has a report about the outbreak of Shiga toxin-producing E. coli O121 infections in Canada that were associated with flour. That outbreak sickened at least 30 people.


Patients affected in this outbreak lived in three provinces when the illnesses were first discovered. PulseNet Canada identified a cluster of six E. coli non-O157 isolates with a matching PFGE pattern on December 29, 2016. An investigation was launched in January 2017.

Patient illness onset dates ranged from November 2016 to April 2017. As of May 23, 2017, a total of 29 cases were identified in Alberta, British Columbia, Newfoundland and Labrador, Ontario, Quebec, and Saskatchewan. Eight patients were hospitalized, and one developed hemolytic uremic syndrome (HUS). One additional case was identified in a U.S. resident who traveled to Canada during this time period.

Initial interviews did not identify any common food source that could have been the source of the outbreak, so patients were re-interviewed using an “open-ended” approach. This approach revealed that exposure to raw flour and dough was common. Some patients provided flour from their homes for testing.

In March 2017, E. coli O121 with the PFGE outbreak pattern was isolated from an open flour sample taken from a patient’s home, and a closed sample collected at a retail store. Both samples had the same brand and the same production date. A product recall was issued at that time. More sampling of the flour was conducted, so many additional recalls of flour and many secondary recalls were issued.

As of May 23, 2017, 22 patients had been asked about flour exposure the week before they got sick. Sixteen, or 73%, said that the implicated brand of flour was used or probably used during the exposure period. Eleven of those sixteen patients said they ate or probably ate raw dough.

This was the first national outbreak of non-O157 Shiga toxin-producing E. coli infections identified in Canada and the first Canadian outbreak linked to flour. But an outbreak in the U.S. last year was linked to recalled General Mills flour. And an outbreak in linked to Nestle cookie dough in 2009 was also caused by raw flour.

In the General Mills flour outbreak, 63 people in 24 states were sickened with the outbreak strains of STEC O121 or STEC O26. Seventeen ill persons were hospitalized. One person developed HUS. No deaths were reported. All evidence found that flour produced at a General Mills facility in Kansas City, Missouri was the likely source of this outbreak.

In the outbreak linked to Nestle cookie dough, 72 people in 30 states were sickened. Ten of those patients developed HUS. On June 29, 2009, the FDA announced that a culture of a sample of prepackaged Nestle Toll House refrigerated cookie dough yielded E. coli O157:H7.

These outbreaks are a good reminder to not eat raw dough or batter, and to handle flour with care. Flour is a raw agricultural product and can be contaminated with pathogenic bacteria just like any other product, including raw meats and produce. Always clean kitchen surfaces, utensils, cutting boards, and cupboard handles after you use flour. Wash your hands well with soap and water after touching flour and uncooked products made with it. And never make a recipe that calls for flour and is uncooked. In addition, don’t make homemade clay products with flour.

The symptoms of an E. coli infection include serious and severe abdominal cramps, diarrhea that may be bloody and/or watery, and a mild fever. Symptoms usually begin three or four days after exposure to the bacteria. Some people, especially children under the age of five, develop an illness called HUS with this infection. HUS is a form of kidney failure and can be fatal..


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