A type of bacteria found in meat and pre-cooked food left at unsafe temperatures was responsible for sickening hundreds of people who ate at a Chipotle Mexican Grill (CMG.N) restaurant in OH, local health officials said on Thursday.
However, it was not certain exactly which food caused the illness and testing is still being conducted by the US Centres for Disease Control.
Chipotle CEO Brian Niccol said the retraining will start next week and the daily routine will be augmented.
The burrito chain will not close any restaurants and will add a recurring online employee assessment for food safety standards.
The outbreak, which occurred between July 26 and July 30 at the Sawmill Parkway restaurant in Powell reportedly affected 647 people who said they experienced gastrointestinal symptoms, including vomiting, diarrhea and stomach pains after eating Chipotle's food products.
Shares of Chipotle were down 3 percent Thursday afternoon.
So far, a particular food was not identified as the source of the bacteria.
And it is facing a federal criminal investigation into food-related illnesses at its restaurants, including norovirus, dating back three years.
In a statement to FOX Business, Chipotle's new CEO Brian Niccol, who formerly lead Taco Bell, said the company "has a zero-tolerance policy for any violations of our stringent food safety standards and we are committed to doing all we can to ensure it does not happen again". In 2016, Chipotle shut all its stores for a few hours for food safety training. Employees were let go from the OH location following the outbreak, but the company would not say how many.
A logo of Chipotle Mexican Grill is seen on one of their bags in Manhattan, New York November 23, 2015.
Niccol added that Chipotle closed the Powell location after people fell ill, and that it cleaned and sanitized the restaurant and replaced all of the food.
Most recently, the company began testing out new additions to its menu, including bacon and nachos.