Health officials intensify investigation as the number of E. coli cases rises, with McDonald’s slivered onions identified as the likely source of contamination.

Health officials, including the FDA and CDC, are actively investigating a multistate outbreak of E. coli O157 infections linked to slivered onions served in McDonald’s Quarter Pounder burgers in specific states.

The outbreak, first identified in early November, has affected 104 individuals across 14 states, as of November 13, 2024.

According to data, of the 98 cases with accessible information, 34 people have required hospitalization, and four have developed hemolytic uremic syndrome (HUS), a life-threatening condition that can lead to kidney failure. Tragically, an older adult in Colorado has died, though the individual did not suffer from HUS.

An overwhelming majority of those infected, 80 of 81 interviewed, reported eating at McDonald’s before falling ill, and 63 of the 75 people who recalled specific menu items mentioned options containing slivered onions.

This strong correlation has led investigators to focus on onions as the likely source. Health officials, including the FDA, Colorado Department of Agriculture (CDA), and Colorado Department of Public Health and Environment (CDPHE), have conducted sampling and environmental testing at various McDonald’s locations, distribution centers, and associated supply firms.

In a sample from recalled onions, E. coli was detected; however, it was identified as a non-O157 strain, specifically E. coli O168, with the Shiga toxin gene stx2a, which does not match the outbreak strain linked to the illnesses. Further testing and genome sequencing are ongoing to provide additional insights into the contamination source.

In response to the outbreak, McDonald’s temporarily halted the use of slivered onions in Quarter Pounder burgers in the affected states. On October 22, 2024, Taylor Farms, one of the major suppliers, issued a recall for their yellow onions, advising food service customers to cease sales and service of the affected product. Subsequently, McDonald’s has resumed serving slivered onions sourced from a different supplier, ensuring there is no continuing risk to public health at their locations.

The FDA has conducted thorough onsite inspections at the Taylor Farms processing facility in Colorado and an onion grower in Washington state. Currently, Taylor Farms and the FDA are collaborating to assess if further recalls are required for downstream customers who may have received onions from the impacted batches. “Food service customers should not be further distributing recalled onions,” as stated in the report, underscoring the need to contain the distribution of potentially contaminated onions.

As the investigation continues, officials urge food service providers and retailers to adhere to recall instructions to prevent further exposure.

Authorities have reassured the public that all necessary measures have been taken, and, according to available information, recalled onions are not expected to be on grocery store shelves. FDA and CDC officials, along with state health departments, remain vigilant and continue to monitor the situation closely, with further updates anticipated once additional sample results are available.

Case Count

• Total Illnesses: 104
• Hospitalizations: 34
• Deaths: 1
• Last Illness Onset: October 21, 2024
• States with Cases: CO, IA, KS, MI, MO, MT, NE, NM, NC, OR, UT, WA, WI, and WY
• Recalled Onion Distribution*: CO, IA, ID, KS, MO, MT, NE, NM, NV, OK, UT, and WY

*Distribution has been confirmed for states listed, but product could have been distributed further, reaching additional states.