On Thursday, Yum Brands—owner of KFC, Pizza Hut, and Taco Bell—followed that lead, saying it, too, would remove fresh onions from its chains' menus at some locations, according to Reuters. Restaurant Brands International, owner of Burger King, also did the same.

"We've been told by corporate to not use any onions going forward for the foreseeable future," Maria Gonzales, the on-duty manager inside a Burger King in Longmont, Colorado, told Reuters on Wednesday. "They're off our menu."

As of Thursday, the case count in the E. coli outbreak remained at 49 people in 10 states. Of those, 10 were hospitalized, including a child with a life-threatening complication. One older person in Colorado has died.

The states with cases include: Colorado (26 cases), Nebraska (9), Utah (4), Wyoming (4), and one case each in Iowa, Kansas, Missouri, Montana, Oregon, and Wisconsin.

McDonald's removed Quarter Pounders and slivered onions from restaurant menus in Colorado, Kansas, Utah, Wyoming, and portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma. In a statement, McDonald's said that for these restaurants, its onions are "sourced by a single supplier that serves three distribution centers. The fast-food giant continues to serve other beef burgers and diced onions at impacted locations.