A deadly E. coli outbreak linked to McDonald's's Quarter Pounders has caused 75 cases in 13 states, the Centers for Disease Control and Prevention said Friday, as it investigates the source of the spread.
The outbreak has led to 22 hospitalizations and one previously reported death of an older adult in Colorado.
Of 61 patients with available information, 22 have been hospitalized and two people have developed a serious condition that can cause kidney failure, called hemolytic uremic syndrome. All 42 people interviewed by the CDC reported eating at McDonald's, while 39 people reported eating a beef burger, the agency said.
People with infections ranged in age from 13 to 88, according to the CDC. The agency reiterated that the number of cases in the outbreak is likely much higher than what has been reported so far. The CDC added that the outbreak may not be limited to states with related cases. This is because many patients do not get tested for E. coli and recover from an infection without receiving medical care, the CDC said. It also typically takes three to four weeks to determine whether a sick person is part of an outbreak.
Shares of the restaurant chain closed down 3% on Friday. The stock has fallen 7% since the CDC announced the outbreak on Tuesday, initially citing 49 cases and one death in 10 states.
McDonald's declined to comment on the update, citing the company's statement when the outbreak was first announced.
Quarter Pounder burgers are a McDonald's menu staple and rake in billions of dollars a year.
Health officials are closely examining the cut onions used in the Quarter Pounder as a possible contaminant. McDonald's has instructed restaurants in the affected area to remove chopped onions from their supply and has stopped distribution of that ingredient in the region.
McDonald's stores in Colorado, Kansas, Utah, Wyoming, as well as parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma, have temporarily stopped using Quarter Pounder sliced onions and beef patties, according to the CDC.
McDonald's identified California-based agricultural giant Taylor Farms as the supplier of the sliced onions that the company eliminated from its supply chain. Taylor Farms has recalled four raw onion products due to possible E. coli contamination. king burger, Pizza Hut, KFC and Taco Bell have removed onions from select restaurants in response to the outbreak.
But federal agencies are also investigating Quarter Pounder beef as a possible culprit.
While the CDC and other federal agencies track cases and work to contain the outbreak, McDonald's has removed Quarter Pounders from restaurants in affected areas. About a fifth of McDonald's restaurants in the United States do not sell Quarter Pounder burgers.
McDonald's spokespeople said Wednesday that it is too early to know if the outbreak is having any effect on traffic to its restaurants.
The company is expected to report its third-quarter earnings on Tuesday and could share more details with investors about the situation on the conference call.
The outbreak comes after several quarters of weak sales for McDonald's in the United States. Price-sensitive consumers haven't visited restaurants as much, prompting McDonald's and other fast-food chains to turn to value-priced meals to boost sales. Wall Street analysts expect the company to report U.S. comparable sales growth of 0.5% for the third quarter, according to StreetAccount estimates.
For now, McDonald's is trying to assure its customers that its menu items are safe to eat and drink and that it is taking the outbreak seriously. Experts told CNBC that barring a more serious crisis, the damage to your brand may be minimal, as was the case with an E. coli outbreak linked to Wendy's Two years ago.
