The foods most commonly linked to E. coli outbreaks are raw or undercooked ground beef, leafy greens, raw milk and soft cheeses, sprouts, and, more surprisingly, raw flour. The bacteria live in the intestines of cattle and other animals, and contamination happens when those organisms reach food through processing, irrigation water, or wildlife contact.
Ground Beef and Other Meats
Ground beef is the most well-known source of dangerous E. coli strains. When a cow is slaughtered, bacteria from its intestines can transfer to the meat surface. With a steak, searing the outside kills those bacteria. But grinding mixes surface contamination throughout the entire product, so a burger that’s pink in the middle may still harbor live organisms. The USDA recommends cooking ground beef to an internal temperature of 160°F, measured with a food thermometer. Color alone is unreliable: some ground beef turns brown before reaching a safe temperature, while other patties still look pink at 160°F.
Raw or undercooked poultry can also carry E. coli, though it’s more commonly associated with Salmonella and Campylobacter. The same cooking principles apply: heat the center of the meat thoroughly.
Leafy Greens and Fresh Vegetables
Lettuce, spinach, and other leafy greens have been behind some of the largest E. coli outbreaks in the U.S. Because these foods are eaten raw, there’s no cooking step to kill bacteria before they reach your plate.
Contamination typically starts in the field. Wildlife feces are a major pathway. A well-documented 2006 spinach outbreak was traced back to wild pigs. Rain or overhead irrigation can splash bacteria from animal droppings onto nearby crops, and studies show that the closer a plant is to a fecal source, the higher the contamination levels. Agricultural water drawn from streams or canals near livestock operations poses a similar risk. Once bacteria reach the leaves, washing helps but doesn’t eliminate them entirely, especially if organisms have been taken up through the roots or lodged in crevices.
Onions made national headlines in late 2024 when fresh, slivered onions served at McDonald’s were identified as the likely source of an E. coli O157:H7 outbreak. That outbreak sickened 104 people across 14 states, hospitalized 34, and caused one death. Of the 75 people who remembered what they ordered, 84% had eaten a menu item containing the raw onions. Root vegetables like onions can pick up bacteria from contaminated soil or water during growing or processing.
Raw Milk and Unpasteurized Cheese
Pasteurization exists specifically to kill pathogens like E. coli, Salmonella, Listeria, and Campylobacter. Raw milk skips that step, and the CDC identifies it as a recurring source of E. coli infections. Soft cheeses made from raw milk carry the same risk because the bacteria can survive the cheesemaking process. Hard, aged cheeses are generally safer because the long aging period and low moisture create conditions less hospitable to bacteria, but they’re not risk-free when made from unpasteurized milk.
Unpasteurized fruit juices, especially apple cider, have also caused outbreaks. Fallen apples that contact animal feces on the ground can introduce bacteria into the pressing process.
Raw Flour and Dough
This one catches many people off guard. Most flour is a raw agricultural product, and processing steps like grinding and bleaching don’t kill bacteria. Grain can pick up E. coli while still growing in the field, from animal waste used as fertilizer or from wildlife. Those germs survive all the way to the bag of flour on your shelf. Tasting raw cookie dough, cake batter, or any unbaked mixture made with flour puts you at risk. The bacteria die only when the flour is baked or cooked to a high enough temperature.
This also applies to children’s craft projects that use raw flour, like homemade playdough.
Sprouts
Alfalfa, clover, mung bean, and other sprouts grow in warm, humid conditions that are ideal for bacterial multiplication. If even a small number of E. coli cells are present on the seeds, they can multiply rapidly during sprouting. Cooking sprouts reduces the risk, but most people eat them raw in salads or on sandwiches, which is why sprouts appear repeatedly in outbreak investigations.
How E. Coli Makes You Sick
Not all E. coli strains are dangerous. Many live harmlessly in your gut. The ones that cause foodborne illness, particularly the Shiga toxin-producing strains like O157:H7, release toxins that damage the lining of the intestines. Symptoms typically include severe stomach cramps, watery diarrhea that often becomes bloody, and sometimes vomiting or a low fever.
Most people recover within five to seven days without treatment. The serious concern is a complication called hemolytic uremic syndrome, or HUS, which damages red blood cells and can lead to kidney failure. About 8 in 10 children who develop HUS have a Shiga toxin-producing E. coli infection. Warning signs include urinating less than usual, unusual paleness in the cheeks or inner eyelids, unexplained bruising or tiny red spots on the skin, blood in the urine, and extreme fatigue or confusion. HUS is a medical emergency, particularly in young children and older adults.
Reducing Your Risk at Home
Cross-contamination is one of the most common ways E. coli spreads in a kitchen. If you cut raw ground beef on a cutting board, then slice tomatoes on the same board without washing it, the bacteria transfer directly to a food you won’t be cooking. Use separate cutting boards for raw meat and ready-to-eat foods, and wash boards, knives, and countertops with hot soapy water after any contact with raw meat.
For produce, rinse leafy greens under running water even if the package says “pre-washed.” This won’t eliminate every bacterium, but it reduces the load. Refrigerate cut produce within two hours, and keep your fridge at 40°F or below to slow bacterial growth.
With ground beef, a food thermometer is the only reliable way to confirm you’ve reached 160°F. Insert it into the thickest part of the patty. For raw flour, the fix is simple: don’t eat uncooked dough or batter, and keep raw flour away from foods that won’t be heated. If you want to make edible cookie dough, you can heat-treat flour in the oven at 350°F for about five minutes before mixing it into a no-bake recipe.