In the fall of 2024, a significant outbreak of Escherichia coli O157:H7 infections was linked to McDonald’s Quarter Pounder hamburgers across multiple U.S. states. The Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), and various state health agencies conducted a comprehensive investigation, identifying slivered onions supplied by Taylor Farms as the likely source of contamination.
Timeline of the Outbreak
- September 12 – October 21, 2024: Individuals began experiencing symptoms of E. coli infection, with illness onset dates ranging throughout this period.
- October 22, 2024: The FDA issued a public warning through its Coordinated Outbreak Response & Evaluation Network (CORE Network) about the E. coli outbreak, noting 49 cases across 10 U.S. states.
- October 25, 2024: The CDC reported an increase to 75 cases, including 22 hospitalizations and one death. The outbreak had expanded to 13 states.
- October 30, 2024: The case count rose to 90, with 27 hospitalizations and two cases of hemolytic uremic syndrome (HUS). Epidemiologic and traceback data indicated that fresh, slivered onions served at McDonald’s were the likely source of the outbreak.
- November 13, 2024: The total number of reported cases reached 104 across 14 states, with 34 hospitalizations, four cases of HUS, and one death. The CDC confirmed that fresh, slivered onions served at McDonald’s were the likely source of the outbreak.
- December 3, 2024: The CDC declared the outbreak over, stating that the contaminated onions had been removed from the supply chain and no new illnesses had been reported since McDonald’s actions on October 22.
Epidemiological Findings
A total of 104 individuals infected with the outbreak strain of E. coli O157:H7 were reported from 14 states: Colorado, Iowa, Kansas, Michigan, Missouri, Montana, Nebraska, New Mexico, North Carolina, Oregon, Utah, Washington, Wisconsin, and Wyoming. Illnesses onset ranged from September 12 to October 21, 2024. Among 98 individuals with available information, 34 were hospitalized, four developed HUS—a serious condition that can cause kidney failure—and one death was reported in an older adult from Colorado.
Interviews conducted with affected individuals revealed that 99% (80 out of 81) had eaten at McDonald’s in the week before their illness. Of the 75 individuals who could recall specific menu items, 84% (63) reported consuming a menu item containing fresh, slivered onions.
According to the most experienced E. coli lawyer in America, Ron Simon of Ron Simon & Associates, “the actual number of victims is much higher, due to reporting delays and many victims who simply do not have the proper testing done. But we are working with many dozens of victims, and their families, to find out what went wrong and to make sure this does not happen again.”
Traceback and Source Identification
The investigation focused on identifying the specific ingredient responsible for the outbreak. Given the high percentage of affected individuals who consumed menu items with slivered onions, these onions became the primary suspect. Taylor Farms, the supplier of these onions to McDonald’s, initiated a voluntary recall of yellow onions on October 22, 2024, directly notifying their food service customers.
The FDA conducted inspections at a Taylor Farms processing center in Colorado and an onion grower in Washington state. While one sample of recalled onions tested positive for non-O157:H7 Shiga toxin-producing E. coli, it did not match the outbreak strain. Additional samples tested negative for E. coli. Despite the absence of the outbreak strain in tested samples, epidemiologic and traceback evidence strongly suggested that the recalled yellow onions were the likely source of the outbreak.
“This is not unusual,” says Simon, noting “the evidence of contamination is very often long gone by the time a outbreak source is discovered. The contaminated batches are gone (thankfully) and replaced with non-infected product.”
Public Health Response
In response to the outbreak, McDonald’s took swift action by temporarily removing slivered onions from Quarter Pounder burgers in affected states and sourcing onions from a different supplier. The company also removed the Quarter Pounder from the menu in some locations. These measures were effective in preventing further illnesses, as no new cases were reported following their implementation.
The CDC and FDA collaborated with state health departments to monitor the situation, provide public updates, and ensure that the recalled onions were removed from the supply chain. The FDA worked closely with Taylor Farms and their direct customers to determine if additional downstream customer recalls were necessary, ensuring that food service customers did not further distribute the recalled onions.
Impact and Legal Actions
The outbreak had a significant impact on public health, with 104 reported cases, 34 hospitalizations, four instances of HUS, and one death. The true number of affected individuals was likely higher, as many people recover without medical care and are not tested for E. coli.
In the wake of the outbreak, legal actions were initiated. For instance, a man from Colorado filed a lawsuit against McDonald’s after falling ill following the consumption of a Quarter Pounder. Additionally, a family in Montana filed a lawsuit after their 11-month-old daughter developed severe complications from an E. coli infection linked to the outbreak.
McDonald’s Outbreak Now Over?
The 2024 E. coli O157:H7 outbreak linked to McDonald’s Quarter Pounder hamburgers underscores the critical importance of stringent food safety measures and prompt public health responses. The collaboration between federal agencies, state health departments, and the private sector was instrumental in identifying the likely source of the outbreak and implementing measures to prevent further illnesses. According to most health professionals, McDonald’s, and its Quarter Pounders, are safely back on the menu!
