Raw cookie dough’s flour could make you really sick | Science News for Students

Raw cookie dough’s flour could make you really sick

Scientists linked one recent food-poisoning outbreak to bacteria in flour
Dec 20, 2017 — 6:45 am EST
cookie dough

In 2015 and 2016, E. coli-tainted flour sickened dozens of people in the United States. Most had eaten raw dough or batter while baking.


Eggs have long been condemned for making raw cookie dough a dangerous, forbidden pleasure. But they can stop taking all the blame. Here’s a new reason to resist the sweet uncooked temptation: flour.

The seemingly innocuous pantry staple can harbor strains of E. coli bacteria that make people sick. Flour is not a particularly common source of foodborne illness. But it has been implicated in two E. coli outbreaks in the United States and Canada in the last two years.

The U.S. outbreak sickened 63 people between December 2015 and September 2016. Pinning down tainted flour as the source was trickier than the average food-poisoning investigation. Researchers described their hunt, last month, in the New England Journal of Medicine.

Usually, state health departments rely on standard questionnaires to find a common culprit for a cluster of reported illnesses, says Samuel Crowe. And, he notes, flour isn’t usually tracked on these surveys. Crowe is an epidemiologist (Ep-ih-dee-me-OLL-uh-gizt) — health detective — at the Centers for Disease Control and Prevention in Atlanta, Ga. He also led the study.

The initial investigation yielded uncertain results. That’s when public health researchers turned to in-depth personal interviews with 10 people who had fallen ill.

Crowe spent up to two hours asking each person detailed questions about what he or she had eaten around the time of getting sick. Asking people what they ate eight weeks ago can be challenging, Crowe says. Many people can’t even remember what they ate for breakfast that morning.

“I got a little lucky,” Crowe says. Two people remembered eating raw cookie dough before getting sick. They each sent Crowe pictures of the bag of flour they had used to make the batter. It turned out that both bags had been produced in the same plant. That was a “pretty unusual thing,” he adds.

Follow-up questioning helped Crowe and his team pin down flour as the likely source. Eventually, scientists at the U.S. Food and Drug Administration analyzed the flour. They isolated strains of E. coli bacteria that produce Shiga (SHE-guh) toxin. This poison makes people ill. It’s what can make E. coli deadly.

Disease-causing bacteria, including E. coli, usually thrive in moist environments, like bags of prewashed lettuce. But the bacteria can also survive in a dried-out state for months and be re-activated with water, says Crowe. So as soon as dry flour mingles with eggs or oil, dormant bacteria can reawaken and start to replicate.

Cookie dough wasn’t the culprit in every case. A few children who got sick had been given raw tortilla dough to play with while waiting for a table at a restaurant. But the cases all involved wheat flour from the same facility. That led to a recall of more than 250 flour-containing products.

There are ways to kill bacteria in flour before it reaches grocery store shelves. However, they aren’t in use in the United States. Heat treatment, for example, will rid flour of E. coli and other pathogens. But the process also changes the structure of the flour. This affects the texture of baked goods, says Rick Holley. He’s a food safety expert at the University of Manitoba in Canada who wasn’t part of the study. Irradiation, used to kill parasites and other pests in flour, might be a better option, Holley says. But it takes a higher dose of radiation to zap bacteria than it does to kill pests.

Or, of course, people could hold out for warm, freshly baked cookies. 

Power Words

(for more about Power Words, click here)

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

Centers for Disease Control and Prevention     , or CDC An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

dormant     Inactive to the point where normal body functions are suspended or slowed down.

E. coli     (short for Escherichia coli) A common bacterium that researchers often harness to study genetics. Some naturally occurring strains of this microbe cause disease, but many others do not.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

epidemiologist     Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

Food and Drug Administration     (or FDA) A part of the U.S. Department of Health and Human Services, FDA is charged with overseeing the safety of many products. For instance, it is responsible for making sure drugs are properly labeled, safe and effective; that cosmetics and food supplements are safe and properly labeled; and that tobacco products are regulated.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

outbreak     The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

pathogen     An organism that causes disease.

questionnaire     A list of identical questions administered to a group of people to collect related information on each of them. The questions may be delivered by voice, online or in writing. Questionnaires may elicit opinions, health information (like sleep times, weight or items in the last day’s meals), descriptions of daily habits (how much exercise you get or how much TV do you watch) and demographic data (such as age, ethnic background, income and political affiliation).

radiation     (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

Shiga toxin    An extremely potent poison secreted by some bacteria — notably E. coli and Shigella dysenteriae — which can live in the digestive tract. This toxin acts on the cells that line blood vessels. Once inside these cells, part of the toxin disables the operations of the cell, leading to its death. As the cells lining the blood vessels die, the host (perhaps a person) can begin to hemorrhage blood. That’s why one early symptom of shiga toxicity is bloody diarrhea.

staple     (in nutrition) A food that serves as a dominant source of calories for a community or species. In people, for instance, just three plants — rice, corn (maize) and wheat — account for roughly 60 percent of calories eaten (according to the United Nations Food and Agricultural Organization). That makes these staples. But the amounts can vary by community. In Africa, for instance, cereal grains (such as corn, wheat and rice) provide almost half of the calories eaten, with roots and tubers (such as yams) providing another 20 percent and meats accounting for just 7 percent. But in Western Europe, meat and other animal products account for almost one-third of calories. Cereals there provide another 26 percent and root and tubers just 4 percent. So there, animal products and cereals are the staples.

strain     (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs.

survey     (v.) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.

toxin     A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.


Journal:​ S. Crowe et al. Shiga toxin-producing E. coli infections associated with flourThe New England Journal of Medicine, Vol. 377, November 23, 2017. doi:10.1056/NEJMoa1615910.