A couple of weeks ago Duncan Hines brand cake mixes were recalled because of Salmonella. Maybe it was the flour. Flour comes from dried wheat that’s milled and not heat treated (because it messes with the gluten). As the Salmonella dries out it gets hardier and survives for months (or longer).

In 2016 pathogenic E. coli (both O121 and O26 serogroups) was the culprit in another raw flour outbreak. The good folks involved with that investigation (Crowe and colleagues) published their findings this week in the New England Journal of Medicine.

The outbreak began in December 2015 and lasted through to September 2016. Fifty-six cases in 22 states were identified.

The biggest takeaway for me was this (such a great explanation of how an investigation works):

Open-ended telephone interviews then were conducted with 10 patients, all of whom stated that they baked frequently or regularly consumed home-baked foods. Five of the patients recalled baking during the week before illness onset, and 3 others reported thatthey might have baked during that period. Of the 5 case patients who remembered baking, 4 reported eating or tasting homemade batter or dough, 3 of whom used brand A flour. The fourth used either brand A or another brand. Two of the patients (a resident of Colorado and a resident of Washington) still had the bags of brand A flour that they had used in the week before illness onset.

Shortly thereafter, state investigators identified 3 ill children who had been exposed to raw flour at restaurants in Maryland, Virginia, and Texas. Restaurant staff had given them raw dough to play with while they waited for their food to be served.

Folks in the media or the hockey arena often ask how these outbreaks get solved. This is how – lots of interviewing, hypothesis generating and then a case-case or case-control analysis. It’s part detective work, part statistics and all science. Sometimes the interviews are messy but this one shows what happens when it works.

Trace-back investigation of the two bags of brand A flour collected from patients in Colorado andWashington revealed that the flour from Colorado was unbleached all-purpose flour manufactured on November 14, 2015, and the flour from Washington was bleached all-purpose flour manufactured on November 15, 2015. The two bags were produced in the same facility. The flour that was used in the raw dough given to the children exposed in the Maryland, Virginia, and Texas restaurants also was from this facility, as was flour from three additional bags collected from case patients residing in Arizona, Califor- nia, and Oklahoma.