CNN
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Fresh onion slices served on McDonald's Quarter Pounders were likely the source of an E. coli outbreak that has resulted in one death and illness in more than a dozen states, the U.S. Centers for Disease Control and Prevention said and the US Food and Drug Administration on Wednesday.

Additional cases related to the outbreak were also reported, bringing the total number of illnesses to 90 and hospitalizations to 27. However, the CDC notes that the current risk to the public is “very low” because the reported illnesses occurred before those affected were removed from food service establishments.

“It is not necessary to avoid consumption of onions or other foods prepared with onions,” the CDC said.

Last week, supplier Taylor Farms recalled four onion products due to “potential E. coli contamination.” McDonald's stores in affected areas have temporarily stopped using slivered onions, and other fast food restaurants that have purchased onions from this supplier – including Burger King, Taco Bell, Pizza Hut and KFC – have proactively stocked fresh onions at some locations removed from their menus.

The recalled onions are unlikely to have gone to grocery stores or directly to consumers, the CDC said Wednesday. According to the FDA, diced onions used at McDonald's have also not been linked to this outbreak.

The beef patties used in Quarter Pounders were also part of the investigation, which began Oct. 22. However, the Colorado Department of Agriculture said Sunday that McDonald's fresh beef patties used in the Quarter Pounder had tested negative for E. coli, and the U.S. Department of Agriculture's Food Safety and Inspection Service said Monday that the evidence did not suggest that ground beef was the likely source of the E. coli outbreak.

McDonald's announced Sunday that it would resume sales of Quarter Pounders at all restaurants this week, but the 900 restaurants that previously received sliced ​​onions from Taylor Farms would not use onions on those sandwiches.