Food poisoning comes from more than undercooked meat, a study published Wednesday in The New England Journal of Medicine warns consumers.

Between December 2015 and September 2016, 56 people in 24 states developed an E. coli infection from eating raw or uncooked flour, reports Samuel J. Crowe, Ph.D., M.P.H., an epidemiologist at the Centers for Disease Control and Prevention (CDC) and the lead author of the study.

And although the outbreak is technically over, the Food and Drug Administration (FDA) and the CDC are still advising that consumers be cautious around flour-containing foods that haven’t been cooked or baked.

"While this stuff sometimes tastes good, it’s really risky behavior and I want to encourage people not to eat raw doughs and batters," says Crowe.

Our list below of five sources of potentially tainted flour will help keep you safe.

Jan. 4, 2018 update: Read “
Avoid Romaine Lettuce for Now, Consumer Reports Says” for details on how this salad green is likely the cause of recent cases of E. coli food poisoning.

What They Found

The outbreak comes from a potentially dangerous strain of E. coli called O121, which can cause abdominal cramps, bloody diarrhea, and kidney damage. It was traced to a General Mills plant in Kansas City, Mo., that produced the contaminated products in November 2015.

No one who became ill from flour or flour-based products has died, but one victim suffered kidney damage and 16 others were hospitalized.

Three children in Maryland, Virginia, and Texas became ill after playing with raw dough given to them by restaurant staff, according to the report. And of the five patients who remembered baking before they got sick, four said they had eaten or tasted homemade batter or dough, and three said they remembered using General Mills brand flour.

More on Foodborne Illness

Between May and July 2016, General Mills voluntarily recalled millions of pounds of possibly contaminated flour, including its Gold Medal, Signature Kitchens, and Gold Medal Wondra flour brands. Several cake and pancake mixes that may have included General Mills flour were also recalled. 

Though the primary source of contamination with the E. coli bacteria is unclear, researchers speculate that a contaminated wheat field may have been to blame.

“These pathogens [E. coli] live naturally in certain animals such as cows and deer, and these animals and their feces are frequently found in wheat fields," says Crowe. "Whenever combines [machines that harvest grain] come through and churn up the wheat to separate it out for processing, they also can pull up some of the feces and other contaminants.”

Other E. Coli Outbreaks From Flour

This outbreak in the U.S. preceded a similar one that occurred in Canada. Between November 2016 and April 2017, 30 people became ill after eating raw flour contaminated with E. coli. This was the first time a particular strain of E. coli, called non-O157, had caused an outbreak in Canada, according to a report published in July in the CDC’s journal Morbidity and Mortality Weekly Report, and the first outbreak linked to flour there in general.

Non-O157 is an understudied strain of E. coli, mostly because labs only recently starting testing for it, according to the CDC. But it has been responsible for outbreaks in the U.S. in the past. As with E. coli O121, non-O157 can cause abdominal cramps and bloody diarrhea but is typically less severe than E. coli O157 (which has been responsible for food-poisoning outbreaks from undercooked ground beef), and is less likely to cause life-threatening kidney damage. However, one patient from the Canadian outbreak did develop a kidney problem. Eleven of those who became ill reported that they either “ate” or “probably ate” raw dough. 

“Given this outbreak and the one in the U.S. last year linked to flour, it’s important for people to know that raw flour can be contaminated and should be cooked or baked thoroughly before eating,” a CDC spokesperson said in July.

5 Sources of Potentially Tainted Flour

The best way to avoid an E. coli infection from flour is to avoid consuming it before it's cooked, but that isn't always so easy. Below are five sources you should watch out for if you want to avoid an E. coli infection. 

1. Raw dough and batters. Products meant to be eaten without cooking, such as cookie dough ice creams, are generally safe, says Crowe, the CDC epidemiologist. But you should assume that everything else—cookie dough, pizza dough, and cake and pancake batters—is risky, so you should be careful not to eat them before they’re cooked.

But raw dough can make you sick even if you don’t eat it. For example, kneading bread dough often leaves you with floury hands, which could be a problem if the flour is tainted. Some restaurants give children balls of uncooked dough to play with, and they might put the dough in their mouth or lick their fingers. Even storing uncooked dough next to other food could pose a risk, so be sure to handle and wrap it carefully.

2. Arts and crafts materials. Websites devoted to pantry-based projects offer recipes for modeling clay, playdough, spray glue, papier mâché, and ornaments with flour as the main ingredient. We recommend that you avoid making these mixtures with kids. 

3. No-cook dishes. Some recipes for truffles, icing, and cookies call for flour but don’t involve heating or baking. If the recipe doesn’t require the dish to be thoroughly cooked, skip it.

4. Contaminated cooking and eating surfaces. Flour is light and powdery, and can easily fly everywhere in your kitchen if you aren’t careful. Even minuscule amounts of tainted flour can make you sick, so be sure that foods that will be eaten raw don’t come into contact with flour-dusted counters, cutting boards, plates, and the like. Wash these—as well as your hands—in hot, soapy water after using them. Be careful if you’re dredging meat or chicken in flour before cooking; you don’t want the flour to go all over the place.

5. Containers you use to store flour. When you purchase a new bag of flour, you might dump the new flour into a bin or canister that has old flour in it, which might be tainted. If you’re not sure whether the old flour has been recalled, throw it out. Make sure that you thoroughly clean the storage container before using it again.

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Bake the Safe Way

The kitchen is one of the busiest hubs in the house, but it also harbors hidden dangers. On the "Consumer 101" TV show, Consumer Reports' experts explain how you can stay safe from E. coli and other contaminants.