What we know about the McDonald’s E. coli outbreak investigation CNNMcDonald’s pulls Quarter Pounders from 20% of all US locations after deadly E. Coli outbreak New York Post Quarter Pounders are off the menu at 20% of McDonald’s in US amid an E. coli investigation The Associated PressMcDonald’s, Food Safety Officials Scrutinize Onions in E. Coli Outbreak The Wall Street JournalTop food safety lawyer says his phones are ‘ringing off the hook’ after McDonald’s E. coli outbreak Business Insider