The Colorado Department of Agriculture reports that burger patties from McDonald’s Quarter Pounders have tested negative for E. coli. Based on that report, the fast food giant has decided to begin reintroducing the popular sandwiches at some restaurants, with full reintroduction expected later this week. McDonald’s stopped selling Quarter Pounder sandwiches in 13 states – representing 20 percent of its 14,000 restaurants in the United States – when an outbreak of infections from E. coli O157:H7 began sickening customers.