Federal agencies Friday reported more cases of E. coli infections linked to meals at McDonald’s restaurants. While none of the sicknesses are in the Chicago area, cases have turned up in Michigan, Missouri, Wisconsin and Iowa.Authorities say people became ill after eating Quarter Pounder burgers and are examining their slivered onions as a possible culprit. In a Friday update, McDonald's said slivered onions purchased from a Colorado Springs location of Taylor Farms "were distributed to approximately 900 McDonald’s restaurants in Colorado, Kansas, Wyoming, and portions of other states in the area. A select number of restaurants were in transportation hubs, such as airports, which may account for illnesses in additional states." It stopped selling Quarter Pounders in targeted states Tuesday.It’s pledging full cooperation with food regulators while emphasizing its other sandwiches are unaffected.Bart Dobek, a Chicago-based food safety consultant, said McDonald’s has an excellent reputation for food handling and cleanliness. But he said problems can occur when fast-food chains don’t properly oversee suppliers.“Everything is connected in the food supply chain,” said Dobek, senior member at BD Food Safety Consultants. He said he advised California-based Taylor Farms several years ago and does not work for McDonald’s.It’s not known if Taylor Farms, which markets salad blends, acquires whole onions from outside growers. It issued a voluntary onion recall covering various customers. The company has not responded to requests for comment.Health officials said the pathogen has made 75 people sick in 13 states, mostly in Colorado, Montana and Nebraska. The U.S. Centers for Disease Control and Prevention said 22 people have been hospitalized and one, an older adult in Colorado, has died.The agency called its efforts “a fast-moving outbreak investigation.” Two infections have been found in Michigan and one each in Wisconsin, Iowa and Missouri.Dobek said E. coli contamination often occurs when produce fields are near cattle farms. Runoff from the cattle farms spreads the bacteria to the produce.That raises the possibility of onion-linked E. coli cases spreading beyond McDonald’s customers. Restaurant chains such as Taco Bell, Pizza Hut, KFC and Burger King have removed onions from some menus as a precaution.Rosemont-based US Foods Holding, a supplier to restaurants and companies in food service, asked customers not to use onions it bought from Taylor Farms Colorado.“Every outbreak like this reflects on the corporate image,” Dobek said. “I expect people will be more vigilant about what goes into the final product.”Some critics have faulted McDonald’s for not closing restaurants in affected areas for a deep cleaning. But Dobek said that step is unnecessary because E. coli spreads mostly through surface contact and not through the air. He said McDonald’s probably knows those surfaces that likely touched the suspected onion slices.As for Taylor Farms, authorities have yet to blame it for the outbreak. But Dobek said it’s probably time for the company to update training for food safety.