McDonald’s worked on October 24 to reassure customers that its U.S. restaurants are safe as federal investigators tried to pinpoint the cause of a deadly E. coli outbreak linked to the fast food giant’s Quarter Pounder hamburgers. McDonald’s pulled Quarter Pounders from one-fifth of its U.S. stores on October 23 as a result of the outbreak, which the U.S. Centers for Disease Control and Prevention (CDC) said had sickened at least 49 people in 10 states. One person died and 10 were hospitalized, according to the CDC. A preliminary investigation by the U.S. Food and Drug Administration suggested fresh slivered onions that are served raw on Quarter Pounder hamburgers were a likely source of the contamination. McDonald’s also serves raw, slivered onions on one of its breakfast sandwiches, but that sandwich isn’t available at the impacted stores. Other burgers, like the Big Mac, use diced, cooked onions. McDonald’s said it was searching for a new regional supplier of fresh onions. In the meantime, Quarter Pounders were removed from menus in Colorado, Kansas, Utah, Wyoming, and portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma. Adriean Madden, 37, pulled up outside a McDonald’s in Denver on October 24 for his usual afternoon snack but then decided against it. He said he was unsure how E. coli spreads or contaminates other foods, and he thinks McDonald’s should be more forthcoming. “This affects my decision with coming to McDonald’s in the future,” Madden said. “I feel like the information isn’t as widely spread. I didn’t see any notices on the door, and then I saw vehicles going through the drive-through just as if nothing was going on.” McDonald’s said it had worked closely with federal food safety regulators in October when it was alerted to the potential outbreak. The company said the scope of the problem and the popularity of its products have complicated efforts to identify the contamination source. McDonald’s has more than 14,000 U.S. stores and serves 1 million Quarter Pounders every two weeks in the affected 12-state area. This article was provided by The Associated Press.