Why the McDonald’s E. Coli Outbreak Still Comes Back to Meat

McDonald’s has an E. coli problem. In October, the Center for Disease Control and Prevention (CDC) announced that McDonald’s Quarter Pounders were the subject of an outbreak that has so far killed one person, and sickened 90 across 13 different states. The beef patty itself is not the cause of the outbreak. Neither is the lettuce, a common source of E. coli outbreaks. This time, the poop is in the onions — but the problem can still be traced back to meat and the factory farms that produce it.

But how, exactly, does a pathogen like E. coli found in intestines and fecal matter make its way onto onions? The answer comes back to processing and the supply chain. The slivered onions were likely processed in a facility where the E. coli was present.

“We’ve never had an E. coli outbreak with onions before,” says Sarah Sorscher, director of regulatory affairs at Center for Science in the Public Interest. “So probably what happened is that there was contamination during the processing after it left the farm.”

E. coli outbreaks in produce are typically caused by contamination from nearby concentrated animal feeding operations. Contaminated dust particles can land on fields of lettuce, for example, or can contaminate irrigation canals. Onions, which have a protective layer of skin separating the vegetable from the world, were likely contaminated off the farm.

 “[The onions were] probably being processed in an environment with ground beef or some other high-risk food, and there was some cross-contamination that happened. Because this is really unusual. But that is a sort of secondary threat that the meat poses,” Sorscher says.

A Widespread Problem

This is not the first foodborne outbreak the U.S. has faced this year. There have been nine multistate foodborne outbreaks in 2024, according to the CDC. Ten people are reported dead from a deli meat listeria outbreak. Two people are dead from a listeria outbreak linked to cheese. McDonald’s joins the latest round of outbreaks.

McDonald’s first major run-in with E. coli (O157:H7) was in 1982, when 47 people in Oregon and Michigan became ill after eating burgers from McDonald’s. Over 40 years later, the bacteria is still making waves in the U.S. food system.

McDonald’s has stated publicly that beef is not the culprit in this outbreak. McDonald’s North America Chief Supply Chain Officer Cesar Piña writes: “The issue appears to be contained to a particular ingredient and geography, and we remain very confident that any contaminated product related to this outbreak has been removed from our supply chain and is out of all McDonald’s restaurants.”

The release outlines that any restaurant that “received slivered onions from Taylor Farms’ Colorado Springs facility will resume sale of Quarter Pounders without [their emphasis] slivered onions.” Affected states include Colorado, Kansas, Wyoming, Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, Oklahoma and Utah.

A Fast Food Legacy of E. Coli

E. coli is a bacteria found in everyone’s gut, including the gastrointestinal tract of cattle. But some strains of E. coli are more dangerous than others. The common strain, O157:H7, is a Shiga toxin-producing strain. When this toxin infects people, they can experience symptoms ranging from diarrhea to hemolytic uremic syndrome, a condition that harms the blood vessels in kidneys, and can be fatal.

This is not the first time this strain of E. coli has been at the center of fast-food controversy. Wendy’s experienced an outbreak in 2022, and Taco Bell had one in 2006. But one outbreak that occurred in the 1990s had lasting impacts on U.S. policy.

In the early 1990s, fast food company Jack in the Box had an E. coli outbreak that killed four children and infected hundreds of people. This particular outbreak was tied to beef in the “Monster Burger,” which was not cooked at a high enough temperature to kill E. coli.

The Jack in the Box outbreak resulted in a long list of policy changes in the food industry. The Food and Drug Administration increased the recommended internal temperature for cooked hamburgers by 15 degrees, the U.S. Department of Agriculture added labeling to raw meat alerting consumers of its dangers and the Food Safety and Inspection Service began testing ground meat for E. coli. In fact, multiple strains of E. coli are now banned in ground beef.

“And illnesses declined,” Sorscher says. “They declined really dramatically, by about 40 percent in the 10 years following implementation of that beef ban.” Now, beef, if cooked at a high enough temperature for long enough, will not carry E. coli to its eater.

But pathogens can still make their way into our bellies. If contaminated meat or its contaminated particles interact with water or equipment or produce, there is a chance for the bacteria to spread. Any of these and more can carry the bacteria, but once it lands on produce, there is a chance it ends up uncooked yet consumed, making its way into the human gut. The result is a rise in the number of cases of produce impacted, says Sorscher.

Tracing Produce Contamination from CAFOs

Lettuce is one produce item that may still give some consumers pause at the grocery store. In 2018, five people died and 96 others were hospitalized after eating lettuce contaminated with E. coli. The lettuce was eventually traced back to the Yuma region of Arizona.

“When [the] FDA went to Yuma to investigate this outbreak, it turns out there’s also a very large, concentrated animal feeding operation that is located in the heart of our winter lettuce bowl,” Sorscher said at a recent conference about industrialized animal agriculture. “The FDA report redacted the name of this facility, but it is not hard to find this CAFO, and the CAFO has advertised that it can hold up to 115,000 head of cattle on site at any given time.”

Large quantities of animals packed together will inevitably produce a lot of manure. In some states, animals in CAFOs produce more waste than people. And it’s not just the manure. Dust particles from waste can migrate into irrigation canals or even leach through the soil from manure pits.

When the FDA went into the CAFO to take samples, they only took six samples before being asked to leave, Sorscher says. In the end, the FDA concluded that they could not draw certain conclusions with such limited sampling.

“As a result of this sort of inability to fully investigate, the source of this outbreak remains under dispute,” she said at the conference. “They did find the outbreak strain in an irrigation canal that flowed past the CAFO and was used to irrigate nearby lettuce fields. But the owners of the CAFO argued that the bacteria couldn’t have gotten in there.”

A number of researchers are studying the different ways pathogens tend to travel in factory farm and meat processing operations. Prashant Singh, a health, nutrition and food science associate professor at Florida State University suggests that the cattle slaughtering process could play a role.

“The first step is removal of the hide,” Singh explains. “In that process, there will be always [be] aerosol pollution and dust creation, because you are really ripping it off, right? Think about a bed sheet: you pull [the hide] with a lot of force. So you can imagine the dust going everywhere. If there was manure on the hide, it aerosolizes, and goes on the meat.”

Another way the bacteria can contaminate raw beef or other items in a slaughterhouse is if the workers damage the gastrointestinal tract when they are removing it from the animal. This can cause bacteria from the gut to contaminate otherwise sterile cuts of beef.

For onions Singh notes, it is incredibly difficult to pinpoint where the contamination occurred.“The meat route is very established. The fresh produce route is a little harder,” he says. Since the onions were slivered, the slicing process is one place where contamination might have occurred. If the slicer was contaminated, it could have easily spread to all sliced onions.

A Weakened Regulatory System

No matter the exact route of contamination, the common factor is the bacteria found in the fecal matter and gut of farm animals. Yet a consistent challenge, Sorscher tells Sentient, is that the meat lobby has worked tirelessly to avoid strict regulation, and the laws that do exist have limits.

“The Poultry Product Inspection Act and the Federal Meat Inspection Act start at the slaughterhouse door,” Sorscher says. Both acts, which include inspection and labeling enforcement, establish standards to prevent contaminated beef and poultry from entering the market. But there are gaps. “They cover slaughterhouses, but not the farms that produce the meat,” says Sorscher. “And the Food Safety Modernization Act through FDA regulates food, but FDA doesn’t regulate animals or animal products,” she says. It falls to the USDA to regulate the product, but the “USDA has this dual interest in promoting agriculture in addition to making sure the food is safe.” In other words, Sorscher adds, “animal farms get special treatment in our current system.”

There are some regulations on the consumer-side but there are limits here too. Unlike ground beef, not all vegetables are tested for E. coli before they hit shelves (some produce, like sprouts, are an exception).

“FDA has so much ground to cover, and they are so thinly spread out,” Singh says. “The meat industry, I feel, is more prepared to handle pathogens than [the] fresh produce [industry].”