Chipotle founder Ells takes over as sole CEO

The changes at the top come as Chipotle's sales and customer traffic still have not recovered, more than a year after an E. coli outbreak first surfaced in 2015.

[...] activist investor Bill Ackman's Pershing Square Capital has taken a nearly 10 percent stake in the chain.

The company has publicized changes to its food safety procedures, given away millions of free burritos, launched a temporary loyalty program and added chorizo to its menu, all to win back customers.