Chipotle Mexican Grill says sick employees sparked the Norovirus outbreak that sickened customers and tarnished its reputation late last year. The chain has been working to regain its footing as a reliable fast-casual chain amid a number of health scares including norovirus, E.Coli, and salmonella outbreaks. The chain closed stores nationwide for an all-staff meeting on Monday, where executives outlined the steps the chain is taking to ensure the safety of its food.