McDonald’s has pulled the Quarter Pounder from about one-fifth of its restaurants over concerns linking the sandwich to an E. coli outbreak, which has killed one and sickened at least 49.

But the quick food giant says consumers should feel secure eating at its restaurants across the U.S., and in parts of the U.S. where the Quarter Pounder has been removed from the menu.

The beef patty and slivered onions put on the patty have been removed from those restaurants in regions where people have reported getting ill and eating a Quarter Pounder, the business said in a briefing on Wednesday.

The U.S. Food and Drug Administration has said onions may be the source of the outbreak. The onions used on the Quarter Pounder arrive from a single supplier in the affected regions, business spokespeople said during the briefing.

McDonald’s has been working with safety regulators since late last week about the potential outbreak when there were fewer known cases, the business said.

Where the Quarter Pounder off the menu:McDonald’s locations in 12 states impacted amid E. coli outbreak

The Centers for Disease Control & Prevention and the FDA announced Tuesday an investigation into Quarter Pounders, in conjunction with the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS), into the outbreak.

Beef patties used in making Quarter Pounders in the affected areas arrive from multiple suppliers, so that makes it a less likely culprit, McDonald’s said. And the FSIS has not yet finished its investigation into beef used, so there’s no finality, the business said. So to protect consumers, McDonald’s has pulled the Quarter Pounder and is also doing its own investigation into the beef and onions used.

“Given the recent events of the history 24 hours, our priority is to reinforce the confidence of American consumers,” McDonald’s USA President Joe Erlinger said Wednesday on NBC’s “Today” display.

“Investigators from all agencies are working quickly to determine the contaminated ingredient,” the CDC said Tuesday.

So for now, the regulatory agencies have preliminarily narrowed the source of the outbreak to either beef patties or slivered onions “and FDA believes that it is the onions,” said Janet Buffer, elder institute manager for the Institute for Food Safety and Nutrition safety with The George Washington University’s Milken Institute School of community Health.

But what about someone who has a hankering for a McDonald’s burger and fries in states where there’s no Quarter Pounder on the menu? Is it really secure? Well, that depends on your capacity for uncertainty, experts declare.

Is it secure to eat at McDonald’s?

OK, if you are eating a burger correct now, put it down, chew and swallow before reading the next sentence.

Since onions are served fresh, they can become adulterated with E. Coli through fecal contamination, which can occur through wastewater, water in the growing area, fertilizer and the proximity of the growing area to livestock, food safety lawyer statement Marler and food scientist and food industry consultant Bryan Quoc Le told USA TODAY.

McDonald’s said suppliers tidy, slice and again tidy onions before they are bagged and refrigerated. Different diced onions are used on regular burgers.

Because the onions are not fully heated before consumption, they can carry that contamination on to the buyer, they said.

There have been significant outbreaks linked to onions and salmonella in the history, Marler said, and the procedure of onions getting contaminated with salmonella is no different than onions getting contaminated with E. coli.

McDonald’s has stringent cooking standards and tests the heat of the Quarter Pounder patties, the business said. That makes onions the likely culprit, Marler said. “It would be unusual to have undercooking happen in 10 different states, so it’s probably a excellent bet it is the onion supplier, but there’s still uncertainty of cross contamination within the restaurants,” he said.

As for eating at the restaurants, he said.”I ponder it’s a little too early to declare McDonald’s is secure to eat at,” Marler said.

However, McDonald’s could boost its safety measures by shutting down the locations where E. coli illnesses happened “to thoroughly tidy them,” because possibly contaminated products did pass through kitchen facilities, Marler said. The potential for cross-contamination could be in sinks, on cutting boards and other food prep surfaces, he said.

“I’m not suggesting all McDonald’s are unsafe to eat at,” Marler said. However, “I ponder at least the restaurants where there are confirmed illnesses linked to it should be shut down for a period of period for a thorough cleaning just in case.”

Quoc Le is more likely to declare McDonald’s remains a “pretty secure bet,” for quick-food fans. Beyond the Quarter Pounder, “there shouldn’t be any concern in terms of eating them,” he said. “McDonald’s is fairly excellent about their logistics and distribution and so they’re able to recall a lot of their products fairly quickly.”

But, he added, “I cruel, for now, probably the next couple of days, you can avoid the Quarter Pounder, but the rest of the items I don’t view there being an issue.”

Consumers should recognize “there is always a level of uncertainty when consuming food, and every person must determine their level of uncertainty tolerance,” Buffer said.

Which states are impacted

These are the states where 49 persons are known to have gotten ill from E. coli infections between Sept. 27 and Oct. 11, the CDC says. One person in Colorado died and 10 people have been hospitalized:

• Colorado (26 cases)
• Iowa (1)
• Kansas (1)
• Missouri (1)
• Montana (1)
• Nebraska (9)
• Oregon (1)
• Utah (4)
• Wisconsin (1)
• Wyoming (4)

McDonald’s pulled the Quarter Pounder off the menu in Colorado, Kansas, Utah and Wyoming, as well as parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, recent Mexico, and Oklahoma.

What is E. coli and what are the symptoms

E. coli, or Escherichia coli, is a type of bacteria that resides harmlessly in the intestines of people and animals. But some E. coli can factor mild to life-threatening gastrointestinal illnesses if consumed, the CDC says.

The types of E. coli that may factor diarrhea usually spread through food or water contaminated with feces contact with animals or people. Animals such as cattle may also spread E. coli to food and food crops. And food handlers can spread infection when they do not use proper hand washing hygiene after using the restroom. 

E. coli infections can factor severe stomach cramps, diarrhea (often bloody) and vomiting for around five to seven days; infections typically occur three to four days after consuming the germ, according to the CDC.

This narrative has been updated to include recent information.

Contributing: Max Hauptman and James Powel, USA TODAY, and Reuters.

pursue Mike Snider on X and Threads: @mikesnider & mikegsnider.

What’s everyone talking about? Sign up for our trending newsletter to get the latest information of the day