Chris Woodyard

USA TODAY

Shares of Chipotle Mexican Grill (CMG) were up 5.4% in late morning trade Wednesday after it was disclosed that investor Bill Ackman has taken a sizeable stake.

In a corporate filing Tuesday, Chipotle said Ackman's Pershing Square Capital Management has bought 2.88 million shares that comprise about 9.9% of the shares outstanding. A major investor showing that kind of faith in the Mexican fast-food chain was enough to drive up shares to $443.90 afterhours up 7.2%, following Tuesday's close at $414.07, up 1.4% for the day.

The investment comes as Chipotle continues to try to work its way back from a health scare involving E. coli and Norovirus that drove away customers. The chain has been focusing on promotions to lure back its most loyal customers, those who frequent the chain for food at least 25 times a year, and students.

Though it has pulled back from its 52-week low of $384.77, Chipotle is still a long ways from its peak share price of $757 -- perhaps a sign that there is still plenty of upside left in the stock.