A proposed class action lawsuit was filed Tuesday against McDonald’s, the latest litigation over the E. coli outbreak linked to the fast-food chain’s Quarter Pounders.

The CDC believes the risk to the public is “very low” due to the actions taken by McDonald’s and Taylor Farms to remove slivered onions from affected locations.

Fresh, slivered onions on the restaurant chain’s Quarter Pounders “are the likely source” of the outbreak, the agency said Wednesday.

The outbreak isn’t expected to have a material impact on McDonald’s business, CFO Ian Borden said.

Shares of McDonald’s have fallen 6% since its Quarter Pounder burgers were linked to a deadly E. coli outbreak.

The Colorado Department of Agriculture’s testing did not detect E. coli in samples of the beef patties taken from McDonald’s restaurants in the area.

McDonald’s provided an update on a multistate E. coli outbreak on Sunday, saying tests have determined Quarter Pounder beef patties aren’t behind the outbreak, and the product will return to affected restaurants in the coming week.

A multistate McDonald’s E. coli outbreak linked to slivered onions served on Quarter Pounders has expanded to even more states with additional people sickened, an update from the Centers for Disease Control and Prevention said Friday.

It is the latest tally of people affected since the agency announced the outbreak on Tuesday, initially citing 49 cases and one death across 10 states.

A slew of fast-food restaurants moved to pull certain ingredients from menu items after an E. Coli outbreak linked to food served at McDonald’s has led to one death and at least 49 people sickened across 10 states.