Why is flour a continuous source of E. coli outbreaks and recalls?

History of outbreaks

Only a small portion (~10%) of all wheat flour milled in the USA is sold directly to consumers through retailers. However, this portion caused several outbreaks in the USA and Canada since the first outbreak in 2009, and is more problematic than the other 90%. 

 

2009

2009 was the first time that flour was the source of an outbreak of heterogenic Escherichia coli Infections (STEC) in commercially prepackaged, ready-to-bake cookie dough. Nestlé Toll House prepackaged cookie dough was identified as the source of the infection. The company recalled 47 products (3.6 million packages of cookie dough)

The CDC reported ^1,2 (that 77 people became ill, 35 were hospitalized, and 10 developed hemolytic uremic syndrome (HUS). The outbreak involved 35 states. A culture of a flour sample collected at the firm, of the recalled prepackaged Nestle Toll House refrigerated cookie dough, detected E. coli O157:H7. This outbreak was the first time that ready-to-bake commercial packaged cookie dough was implicated as a vehicle for STEC infections.

2015-2016

Another outbreak of STEC E. coli in flour happened between December of 2015 and September of 2016.

Sixty-three people were infected with the outbreak strains of STEC O121 or STEC O26 from 24 states.  Seventeen patients have been hospitalized, and one person developed HUS.

The CDC reported that the evidence indicated that flour was produced at a General Mills facility in Kansas City, Missouri. General Mills recalled Gold Medal Flour, Gold Medal Wondra Flour, and Signature Kitchens Flour On May 31, 2016. All the recalled flours were produced in the Kansas City facility and sold nationwide. General Mills expanded its recall on July 1, 2016, and again on July 25, 2016, to include more production dates as more cases of illnesses due to E. coli mounted.

2016-2017

According to the Canadian Food Inspection Agency an outbreak that started on November of 2016-April of 2017 in Canada connected to E. coli STEC O121 was associated with milling by Ardent Mills and Rogers Foods Ltd. It involved Robin Hood brand All Purpose flour.

This outbreak caused 29 people to become ill in six provinces (Alberta, British Columbia, Newfoundland and Labrador, Ontario, Quebec, and Saskatchewan) linked with the consumption of the uncooked flour. Eight patients were hospitalized, and one developed HUS.

On June 7, 2017, Rogers Foods Ltd. recalled the Rogers brand All Purpose flour from the marketplace due to possible E. coli O121 contamination. This outbreak sickened at least six people in British Columbia.  It is not clear if the two Canadian outbreaks and the USA outbreak of E. coli 0121 are related.

A study was present in the contaminated flour,  indicating that larger sample sizes are required to detect these low numbers of E. coli.

2019

The CDC announced on June 15, 2019, that several brands of flour have been recalled due to E. coli 026 contamination. All the flours were milled for the different companies by ADM Milling Co. The first brand to be recalled was of Baker’s Corner All Purpose Flour. The Rhode Island Department of Health found while testing the presence of E. coli 026. The strain of E. coli found in the flour was linked to 17 illnesses in 11 states (Connecticut, Delaware, Massachusetts, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, and West Virginia).

Vermont’s King Arthur Flour was next since they used the same flour as the recalled ALDI product. King Arthur recalled 14,218 cases of Unbleached All-Purpose Flour. It is not clear why it took so long for another potentially contaminated product to be identified. No illnesses were reported in connection with this brand.

The third brand of flour, Pillsbury® has been recalled and is being tied to the ongoing E. coli outbreak.  The flour was manufactured by Buffalo, New York-based ADM Milling Co. According to a notice of the the FDA website, Pillsbury® Best 5 lb Bread Flour is being recalled due to the E. coli. Approximately 4,620 cases have been recalled. The Flour was distributed to a limited number of retailers and distributors across the following 10 states: Connecticut, Delaware, Maryland, Maine, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, and Virginia. No illnesses were reported with the recalled products.

Presence of E. coli on raw wheat and flour

A study published in J. Food protection creates a baseline of the prevalence and levels of pathogens in raw wheat samples taken before milling.  Enterohemorrhagic E. coli (EHEC) was found in 0.44% of the tested samples, with an average count of 0.039 cfu/g. The study concluded that contamination of flour was coming from many sources, and raw flour is likely to be contaminated with pathogens.

Why is the presence of E. coli a problem?

Flour is usually used in products that are baked, and the baking process kills all the E. coli if present. However, many people, especially children, like to eat raw dough. The many outbreaks are a reminder that is it not safe to taste or eat raw dough or batter because they can be contaminated with STEC and other pathogens that can make people sick. The CDC investigators stated: “Foods containing raw flour should be considered as possible vehicles of infection of future outbreaks of STEC (Shiga toxin-producing E. coli) or Salmonella infections.”

What can be done to prevent the problem?

The CDC recommends that food manufacturers should consider the use of heat treated flour in ready-to-cook or ready-to-bake foods that are likely to be consumed without cooking or baking, even if the label requires baking or cooking.

 

According to Food Safety News the Nestle Co. is using heat-treatment process for its raw cookie dough since their outbreak in 2009. However, the flour milling industry and food processors has not embraced heat treatment or irradiation; both methods are known to kill pathogens in flour. The flour Industry is concerned that heat treatment or irradiation harms the rising properties of flour.