A Comprehensive Analysis of Contaminated Onions,McDonald’s Menu Items, and Other Affected Restaurants

I. Overview of the Outbreak

In the fall of 2024, a deadly outbreak of Escherichia coli O157:H7 swept across 14 U.S. states, ultimately sickening at least 104 people, hospitalizing 34, and claiming one life. The outbreak was traced to contaminated slivered yellow onions supplied by Taylor Farms — a California-based produce company — to McDonald’s restaurants primarily in the Midwest and Mountain West regions of the United States. Illness onset dates ranged from September 12 through October 21, 2024, and the CDC formally declared the outbreak “over” on December 3, 2024, following a comprehensive investigation by the FDA, CDC, and multiple state health agencies.

The outbreak was centered on McDonald’s Quarter Pounder hamburgers, which used fresh, raw slivered onions from Taylor Farms’s Colorado Springs processing facility. The pre-sliced onions were packaged at that facility and distributed to approximately 900 McDonald’s locations.

II. Were Taylor Farms Onions Used in Other McDonald’s Menu Items Beyond the Quarter Pounder?

This is one of the most consequential questions arising from the outbreak investigation. The answer is yes — but the evidence in the public record is limited and, in some respects, underreported.

A. The Quarter Pounder: The Primary Vehicle of Illness

Public health investigators confirmed early in the investigation that the fresh, slivered onions from Taylor Farms were a unique ingredient specific to the Quarter Pounder family of burgers. Critically, McDonald’s classic hamburgers, Big Macs, McDoubles, and other standard sandwiches use rehydrated diced onions — not the fresh slivered onions from Taylor Farms. This distinction was central to narrowing the epidemiological investigation.

McDonald’s itself acknowledged this in a company statement, confirming that other beef products — including the Cheeseburger, Hamburger, Big Mac, McDouble, and Double Cheeseburger — were unaffected and remained available for sale during the outbreak.

B. A Breakfast Sandwich Was Also Pulled — A Critically Underreported Fact

One of the most significant — and least discussed — findings of this analysis is that McDonald’s halted sales of at least one breakfast sandwich in the affected states, in addition to the Quarter Pounder. Reporting from Food Safety News confirmed: “[I]n several states, McDonald’s has stop selling Quarter Pounders and a breakfast sandwich, both of which use fresh, slivered onions.”

This is a material fact that was largely absent from mainstream media coverage of the outbreak, which focused almost exclusively on the Quarter Pounder. It confirms that the Taylor Farms slivered onions were not limited to a single menu item.

Which Breakfast Sandwich(es) Were Involved?

The specific breakfast sandwich(es) pulled were not always named in reporting, but McDonald’s breakfast menu includes several steak-based items that explicitly feature slivered or grilled onions as a component:

• Steak, Egg & Cheese McMuffin — described on McDonald’s own website as featuring “grilled onions” on a toasted English muffin.
• Steak, Egg & Cheese McGriddle — a steak-based breakfast sandwich on maple griddle cakes, also featuring slivered/grilled onions at select locations.
• Big Breakfast with Steak — a platter available at select locations that includes steak with slivered onions.

These items stand in contrast to the standard Egg McMuffin, Sausage Biscuit, McGriddle, and other breakfast sandwiches, which do not include fresh onions as an ingredient.

C. The Breakfast Burrito — A Different Type of Onion

McDonald’s Sausage Breakfast Burrito does contain onion as an ingredient. However, the burrito uses diced, pre-cooked onions — not the fresh slivered yellow onions supplied by Taylor Farms from the Colorado Springs facility. There is no public reporting or regulatory finding linking the breakfast burrito to the contaminated onions at issue in this outbreak.

D. What the CDC’s Interview Data Reveals

The CDC’s epidemiological data provides some nuance worth examining carefully. Of 75 people interviewed who could recall specific menu items consumed at McDonald’s, 63 (84%) reported eating a menu item containing fresh, slivered onions. This means approximately 16% of confirmed cases did not specifically recall consuming a slivered onion item — raising questions about whether other vehicles of exposure existed.

In one notable case documented by NBC News, a patient’s CDC report listed meals including a “bowl with chicken and onion” and a “chicken biscuit breakfast sandwich” — but no Quarter Pounder. The CDC also noted that one confirmed patient reported eating a menu item with a fresh quarter-pound beef patty but without slivered onions — an anomaly that investigators flagged.

III. Other Restaurants That Used Taylor Farms Onions — Were Any Implicated?

A. FDA and McDonald’s Confirm Broader Distribution

Both the FDA and McDonald’s explicitly acknowledged that Taylor Farms’s recalled yellow onions were distributed to food service customers beyond McDonald’s. The FDA stated that “recalled yellow onions were sold to additional food service customers” and that those customers were directly notified.

McDonald’s itself confirmed in a formal statement: “We also understand that onions were distributed by this supplier, from this facility, well beyond McDonald’s System (including other quick service restaurants and food service providers).”

US Foods, a major national food distributor, also notified its restaurant clients of the Taylor Farms recall, confirming it distributed these onions to numerous food service operations across the country. Sysco, the nation’s largest food distributor, similarly contacted its customers.

B. Burger King — Confirmed Taylor Farms Customer (5% of U.S. Locations)

Restaurant Brands International, the parent company of Burger King, confirmed that approximately 5% of its U.S. restaurants received onions distributed from Taylor Farms’s Colorado facility. Burger King received whole, uncut onions — which employees then washed, peeled, and sliced on-site — rather than the pre-sliced slivered onions packaged at the Taylor Farms facility that went to McDonald’s. Burger King proactively removed these onions from its affected restaurants without being contacted by health authorities, and reported no illnesses linked to its locations.

C. Yum! Brands (Taco Bell, Pizza Hut, KFC) — Precautionary Onion Removal

Yum! Brands — the parent company of Taco Bell, Pizza Hut, and KFC — issued a statement confirming it had “proactively removed fresh onions from select” restaurants across all three chains, citing an abundance of caution. The company declined to specify exactly how many locations were affected or confirm whether it used Taylor Farms as its supplier. Colorado Taco Bell restaurants and select Pizza Hut and KFC locations in Colorado were specifically confirmed to have removed fresh onions from their menus. No illnesses were reported at any Yum! Brands location.

D. Illegal Pete’s (Colorado/Arizona Burrito Chain) — Confirmed Taylor Farms Customer

Illegal Pete’s, a Denver-based Mexican fast-casual burrito chain with locations in Colorado and Arizona, was among the US Foods customers directly notified of the Taylor Farms onion recall. The chain promptly removed onions from its menus and posted signs at restaurant doors informing customers that menu items containing onions would be temporarily unavailable. The chain’s founder noted that Illegal Pete’s did not use the same pre-sliced slivered onions as McDonald’s Quarter Pounders, and reported zero associated illnesses.

E. Chipotle — Confirmed Non-User

Chipotle Mexican Grill publicly confirmed that it does not source onions from Taylor Farms and does not use any other ingredients from the Colorado Springs facility, removing it from concern during the investigation.

F. No Confirmed Illnesses at Any Restaurant Other Than McDonald’s

Despite the confirmed broad distribution of Taylor Farms onions to multiple restaurant chains, no illnesses were ever epidemiologically linked to any restaurant other than McDonald’s. Of all 81 patients ultimately interviewed by investigators, 80 (99%) reported eating at McDonald’s before becoming ill. No other retail outlet or restaurant chain was identified as a source of illness in the official investigation.

IV. Why McDonald’s Customers Were Most Affected — Key Distinctions

Several structural factors explain why the contamination manifested almost exclusively in McDonald’s customers, even though multiple chains received Taylor Farms onions:

• Pre-sliced vs. whole onions. McDonald’s received onions already sliced and packaged at the Taylor Farms Colorado Springs facility. Any contamination introduced during processing was sealed in the bag and preserved through to consumption. Other chains, including Burger King, received whole onions that were washed, peeled, and cut on-site by employees — potentially reducing but not eliminating risk.
• Raw consumption. The slivered onions on the Quarter Pounder were served completely raw and uncooked. Heat kills E. coli O157:H7, so any onions used in cooked applications (such as grilled or sautéed onions on steak breakfast items) would have presented a substantially lower risk, even if from the same contaminated batch.
• Volume and concentration of distribution. The 900 McDonald’s locations that received onions from the Colorado Springs facility represented a very large, concentrated exposure pool. No other single chain had comparable penetration from this specific facility.
• Epidemiological focus. Because investigators quickly identified McDonald’s as the common exposure location, the interview and traceback process was largely focused on McDonald’s customers. It is possible that some illnesses at other establishments were not captured in the outbreak cluster.

V. Summary: Restaurant Exposure and Response

Restaurant	Taylor Farms Customer?	Form of Onion	Illnesses Reported?	Action Taken
McDonald’s	Yes (pre-sliced slivered)	Pre-sliced, raw, packaged	104 confirmed	Pulled Quarter Pounders & breakfast sandwich; stopped sourcing from Taylor Farms Colorado
Burger King	Yes (whole onions, ~5% of locations)	Whole; cut in-store	None reported	Proactively removed onions at affected locations
Taco Bell	Possible; unclear	Unclear	None reported	Removed onions at Colorado & select locations
KFC	Possible; unclear	Unclear	None reported	Removed onions at select locations
Pizza Hut	Possible; unclear	Unclear	None reported	Removed onions at select locations
Illegal Pete’s	Yes (via US Foods)	Diced/whole (not pre-sliced)	None reported	Pulled onion menu items; sought alternate supplier
Chipotle	No	N/A	None	No action required

VI. Litigation

The outbreak prompted multiple lawsuits against both McDonald’s and Taylor Farms. One of the first was filed on October 23, 2024, by a man who became ill after eating at a McDonald’s location in Greeley, Colorado. Food safety attorney Ron Simon of Ron Simon & Associates, a prominent food safety law firm, represented numerous plaintiffs in the litigation.

VII. Key Conclusions and Takeaways

• The breakfast sandwich connection is real but underreported. McDonald’s confirmed it pulled at least one breakfast sandwich — in addition to the Quarter Pounder — because the item used fresh slivered onions from Taylor Farms. Steak-based breakfast items (Steak McMuffin, Steak McGriddle, Big Breakfast with Steak) are the most likely candidates based on their publicly available ingredient lists.
• The Sausage Breakfast Burrito likely used different onions. While the burrito contains onion, it uses diced, cooked onions — not the fresh slivered yellow onions from Taylor Farms. No public reporting links it to the contaminated batch.
• Taylor Farms onions reached multiple restaurant chains. The FDA, McDonald’s, US Foods, and Sysco all confirmed that the recalled yellow onions were distributed to food service customers well beyond McDonald’s. Burger King, and likely Taco Bell, KFC, Pizza Hut, and Illegal Pete’s, all received onions from this supply chain.
• No confirmed illnesses were ever tied to any restaurant other than McDonald’s. However, the epidemiological investigation was heavily focused on McDonald’s customers from the outset, and the possibility of undetected cases at other establishments cannot be categorically ruled out.
• The form of the onion mattered enormously. McDonald’s pre-sliced, pre-packaged slivered onions — served raw — created ideal conditions for E. coli transmission. Other chains receiving whole onions that were washed, cut in-store, and potentially used in cooked applications faced substantially lower risk profiles.
• The Taylor Farms Colorado Springs facility was the focal point. The FDA conducted on-site inspections at the facility and at an onion grower of interest in Washington State, though no specific grower was ever formally implicated. Taylor Farms maintained throughout the investigation that extensive testing found no evidence of E. coli in its products.

Key Sources

•  CDC Investigation Update (November 13, 2024)

•  FDA Outbreak Investigation Page

•  PBS NewsHour — Outbreak Expands

•  NBC News — How Officials Traced the Outbreak

•  Restaurant Business Online — Onion Recalls

•  Colorado Sun — Illegal Pete’s

•  Axios — Taco Bell, KFC, Burger King Remove Onions

•  Food Network — Chains Remove Onions

•  Fortune — Taylor Farms Linked

•  Washington State DOH

•  Wikipedia — 2024 McDonald’s E. coli Outbreak •  Food Poisoning News — Comprehensive Analysis