17 Feb 2018 //

Shiga Toxin-Producing E.coli Infections: The Possibility of Its Transmission through Flour

Although most kinds of E.coli are harmless and considered as a very important part of a healthy human intestine, some kinds of E. coli bacteria may cause disease if they produce a toxin called Shiga toxin. These bacteria are called “Shiga toxin-producing E. coli,” or STEC for short. Symptoms that may emerge from the Infection of STEC include: a very bad stomach cramps, diarrhea (often bloody), fever and vomiting—which may sometimes be life-threatening. Each year, STEC infections has caused 265,000 illness, 3,600 hospitalizations and 30 deaths in the United States.

STEC infection outbreak in the United States has been reported since 2009. Recent evidence shows that there may be a correlation between the outbreak with the consumption of prepackage cookie dough flour, a case that would that is unexpected as flour is a low-content ingredient and is normally presume to not support bacterial growth. In 2016, a multi-state outbreak investigation in the United States linked infections of STEC, with most of the serogroups are O121 and O26, with a large flour domestic producer. This investigation identified 56 cases in 24 states (shown in Fig. 1); 55 were infected with the O121 serogroups of STEC and 1 was infected with the O26 serogroups. Sixteen cases were hospitalized.

This investigation conducted open-ended telephone interview with 10 patients, with the results as follow: (1) All patients investigated were found to frequently bake or regularly consume home-baked foods, (2) five recalled baking during the week before the onset of the illness emerged, and (3) three stated that they may have baked during the same period. Of the 5 patients who recalled baking, 4 tasted the food, and 3 of whom used brand A flour. Research shows positive correlation between STEC infection, baking with the use of A flour, and tasting uncooked or unbaked homemade dough or batter.


This investigation shows that raw flour was the source of the STEC infection outbreak. In addition to STEC, Salmonella was also reported being able to be transmitted through the consumption of raw flour—showing the importance of baking flour until its cooked before consumption. It is also stated that most of the routine state and national foodborne disease questionnaires do not include questions regarding the consumption of raw or undercooked flour, making epidemiologist to initially be unable to assess any related cases.

As a closing remark, although epidemiological, trace-back of cases and laboratory components were successfully conducted, the source of the contamination of the flour was never identified. Based on what is known about the ingredients of flour, wheat is the ingredient most likely to be contaminated while its processing on filled, with cases are presumably related to the contamination of cattle’s manure—yet this is merely a presumption.



  1. Crowe S, Bottichio L, Shade L, Whitney B, Corral N, Melius B et al. Shiga Toxin–Producing E. coli Infections Associated with Flour. New England Journal of Medicine. 2017;377(21):2036-2043.
  2. coli and Food Safety [Internet]. Centers for Disease Control and Prevention. 2017 [cited 7 December 2017]. Available from: https://www.cdc.gov/features/ecoliinfection/index.html