AP -
NEW YORK (AP) - Chipotle founder and co-CEO Steve Ells says he is "deeply sorry" about the customers who were sickened after eating at the chain in recent weeks.
 
The Centers for Disease Control and Prevention has said that at least 52 people in nine states have been sickened in an E. coli outbreak, with 47 of them having eaten at Chipotle. The most recent case happened Nov. 13.
 
The ingredient that sickened people has not been identified.
 
In an interview on NBC's Today show, Ells repeated the company's pledge to tighten food safety procedures to ensure such incidents do not happen again.
 
Meanwhile, Boston College has raised the number of students who have reported feeling ill after a group of them ate at Chipotle from 120 to 141. The school said that 12 of those students did not eat at the restaurant.
 
Public health officials said Wednesday that norovirus was found at the restaurant. Norovirus can be transmitted by eating contaminated food, or by touching infected surfaces, then putting your fingers in your mouth.