McDonald's is naming the supplier believed to be responsible for causing an E. coli outbreak linked to the company's Quarter Pounders across 10 states that has left one person dead and dozens sick.

It is the latest tally of people affected since the agency announced the outbreak on Tuesday, citing 49 cases and one death across 10 states. Health officials are closely examining the slivered onions used in the Quarter Pounder as a likely contaminant.

Burger King, KFC, and other chains have pulled onions from their products after a potential source of McDonald's E. coli outbreak was identified.