The outbreak investigation showed that roughly half of the 38 people infected used flour, some of them stated using Gold Medal brand. So far, the flour has not tested positive for the organism.
So how does E. coli get into flour? Probably from the raw material. One study looking at a large number of samples, found that 12.8% of flour samples found E. coli (not strain specific) in raw flour.
Of course, if the products made from the flour are properly cooked, that cooking will destroy the organism. However, people do eat raw dough products, including cookie dough. Nestle raw cookie dough was involved in an E. coli outbreak in 2009 where people were probably eating raw cookie dough. In a report of that incident, investigators were not able to find the actual source of the E. coli. And like that case, it is not likely that they will be able to find this strain of E. coli.From that report:
Despite extensive traceback and environmental investigations and testing by regulatory agencies and company A, the source and route of product contamination remains undetermined. Possible means of contamination include introduction of a contaminated ingredient during processing, a lapse in plant biosecurity measures, intentional contamination, or cross contamination with another food processed in the plant. Although the manufacturing plant is located in a rural area in the mid-Atlantic United States, investigators did not observe any obvious breach in biosecurity that would facilitate introduction of E. coli O157 into the facility from the outside. No significant food handling or safety violations were identified at the plant that could result in cross-contamination within the plant.In the end, don't eat raw dough, including cookie dough. Clean up as you go, washing up any spilt flour.
FDA News Release
http://www.fda.gov/Safety/Recalls/ucm504235.htm
Gold Medal, Gold Medal Wondra, and Signature Kitchens Flour Recalled Due to Possible E. coli O121 Contamination