Brian Niccol is Chipotle's new CEO. Founder Steve Ells will become executive chairman. 

Chris O'Meara/AP

Not long ago, Chipotle was on top of the burrito world.  Now the Denver-based company is in dire straits. A string of illnesses in 2015 and 2016 has decimated sales.  A quick turnaround never materialized.  Next week, a new CEO takes the helm for the first time since Chipotle opened near the University of Denver 25 years ago.  CPR business reporter Ben Markus follows the company and joins us to talk more about the challenges.