After McDonald's E. coli outbreak, Yum Brands removes onions from select Taco Bell, KFC, and Pizza Hut locations.

• Some Taco Bell, KFC, and Pizza Hut locations are no longer serving onions due to a change in policy by Yum Brands.
• McDonald's has been under scrutiny due to the E. coli outbreak that has been linked to Quarter Pounder burgers.
• The source of the outbreak may have been the slivered onions served on the burgers, which are being investigated by health authorities.

McDonald's E. coli outbreak has led to the removal of onions from some Taco Bell, KFC, and Pizza Hut locations.

"In response to the E. coli outbreak, Yum Brands has removed fresh onions from select Taco Bell, Pizza Hut, and KFC restaurants as a precautionary measure. The company will continue to follow supplier and regulatory guidance to ensure the safety and quality of its food."

On Wednesday, a restaurant supplier issued a recall notification for four onion products made by Taylor Farms. There is no information on whether Yum removed the onions from certain locations due to the recall.

McDonald's has not publicly named Taylor Farms as a supplier for onions, and U.S. Foods does not distribute onions for McDonald's restaurants. Taylor Farms has not responded to a request for comment from CNBC.

Currently, health authorities are probing the cause of the E. coli outbreak that has resulted in one fatality and 49 confirmed cases in 10 states, including Colorado, Nebraska, and Wyoming. As of Tuesday, the Centers for Disease Control and Prevention have questioned 18 individuals, with 14 recalling eating a Quarter Pounder hamburger from McDonald's.

McDonald's has removed Quarter Pounders from about 20% of its U.S. restaurants due to an investigation into two ingredients in the burgers: fresh beef patties and slivered onions.

McDonald's stated that all affected restaurants obtain onions from a single facility that washes and slices them. In contrast, their beef patties originate from multiple suppliers in the region. If cooked according to their internal standards, the temperature would eliminate any E. coli in the patty.

— CNBC's Kate Rogers contributed reporting for this story.