What McDonald's needs to do next after E. coli outbreak

As McDonald's and health authorities race to contain a deadly E. coli outbreak, the burger chain faces challenges in the months ahead to keep the trust of diners and investors.

Shares of the fast-food giant have fallen 6% since the Centers for Disease Control and Prevention issued an advisory notice Tuesday, warning that the company's Quarter Pounder burgers have been linked to an E. coli outbreak in 10 states that has led to one death.

Health investigators have zeroed in on the slivered onions used in the Quarter Pounder as the likely contaminant. McDonald's confirmed that California-based vegetable producer Taylor Farms is the supplier of onions it removed from its supply chain. Taylor Farms issued a recall on four raw onion products, citing potential E. coli contamination, restaurant supplier U.S. Foods said in a notice to customers Thursday. (U.S. Foods is not a supplier for McDonald's.)

The CDC initially reported 49 people became ill from the outbreak from Sept. 27 to Oct. 11. The tally has now risen to 75 cases across 13 states, including at least 22 hospitalizations, according to a CDC update on Friday. Health experts say the number of cases will likely rise as the investigation progresses.

Just two days after the CDC issued its advisory notice, it's too soon to tell how the outbreak could affect McDonald's business, especially if the case count grows. But investors are already worried that it could cause sales to fall at the company, which has been trying to rebound from lagging traffic by offering deals to price-sensitive customers.

Company spokespeople said Wednesday that's it's far too early to share if the outbreak was having any effect on its restaurants' sales. McDonald's is expected to report its third-quarter