A recent outbreak of E. coli linked to McDonald’s has been traced back to fresh onions supplied by a California grower, according to officials from the fast-food chain. In response, other fast-food chains including Taco Bell, Pizza Hut, KFC, and Burger King have decided to remove onions from certain menu items as a precautionary measure.

McDonald’s confirmed that the onions were shipped from Taylor Farms, based in Salinas, California, to a distribution center, prompting the removal of Quarter Pounder hamburgers from multiple locations across several states. However, the company has not disclosed the specific distribution facility involved.

So far, at least 49 individuals across ten states have reported illnesses related to the contaminated burgers, with one confirmed death. Federal health officials are actively investigating the outbreak and have zeroed in on slivered onions as a likely source of the infections.

U.S. Foods, a prominent food wholesaler, announced that Taylor Farms issued a recall for whole and diced yellow onions due to potential E. coli contamination. These recalled onions were produced at a Taylor Farms facility located in Colorado. A spokesperson for U.S. Foods clarified that they do not supply McDonald’s, and thus, the recall does not pertain to any products offered at the fast-food restaurants.

Multiple requests for comments from Taylor Farms went unanswered. Meanwhile, the U.S. Food and Drug Administration has yet to confirm whether it is investigating the grower, though a representative mentioned that the agency is exploring all potential sources linked to the outbreak.

Other nationwide restaurant chains have taken similar steps, with Yum Brands indicating a temporary halt in the use of fresh onions at select Taco Bell, Pizza Hut, and KFC locations as they monitor the E. coli situation. The company did not provide details on which restaurants were affected or if they shared the same onion supplier as McDonald’s.

Restaurant Brands International, which operates Burger King, stated that 5% of their locations utilize onions sourced from Taylor Farms’ Colorado facility. Employees at these restaurants typically receive whole onions, which are then washed, peeled, and sliced on-site. Even without any notifications from health authorities or indications of illness, the company chose to instruct affected restaurants to dispose of the onions two days prior. They also plan to replenish their supplies from alternative vendors.

Onions have been associated with past foodborne illness outbreaks. In 2015, Taylor Farms recalled a salad mix that included celery and onions, which resulted in 19 people falling ill with E. coli linked to Costco’s chicken salads.

Within the current McDonald’s outbreak, at least ten patients have been hospitalized, including a child experiencing serious kidney complications due to the infection. The illnesses, confirmed between late September and mid-October, were caused by the E. coli 0157:H7 strain, known for producing a hazardous toxin. Each year, this strain is responsible for approximately 74,000 infections in the United States, leading to over 2,000 hospitalizations and 61 fatalities, according to the Centers for Disease Control and Prevention (CDC).

The typical symptoms of an E. coli infection may manifest swiftly, usually within a day or two of consuming tainted food. Common symptoms consist of fever, vomiting, diarrhea (including bloody diarrhea), and dehydration indicators such as reduced urine output, increased thirst, and lightheadedness. The infection poses a greater risk to vulnerable populations, including young children, the elderly, pregnant individuals, and those with compromised immune systems.