Fresh onions are the likely source of an E. coli outbreak at McDonald's restaurants that has sickened 49 people and killed one, the U.S. Department of Agriculture said late on Wednesday, alarming some McDonald's customers and other fast-food chains using onions as an ingredient.

A major supplier of onions has issued a recall amid an E. coli outbreak linked to McDonald’s Quarter Pounder hamburgers

Victims who have been sickened in connection to the deadly E. coli outbreak linked to McDonald's famed Quarter Pounders are already lawyering up. Top food safety attorney Ron Simon of the Houston, Texas-based law firm Ron Simon & Associates told Business Insider Wednesday that his phones have been "ringing off the hook" after federal health officials reported the outbreak Tuesday.