U.S. fast-food chains were pulling fresh onions out of their menu items on Thursday after the vegetable was named as the likely source of an E. coli outbreak at McDonald's restaurants that has sickened 49 people and killed one.

Restaurant Brands International, parent of McDonald's rival Burger King, and Yum Brands said they were removing fresh onions from menu items.

Roughly 5% of Burger King locations have removed onions from the menu, a Burger King spokesperson said in a statement.