Last month Chipotle Mexican Grill closed a location in Powell, Ohio after nearly 650 reported illnesses were tied to the location. The outbreak was caused by Clostridium perfringens, a type of bacteria that thrives at room temperature—in other words, food at this particular Chipotle location may have been kept at unsafe temperatures.

Following this latest incident, the company has decided it will retrain all of its estimated 70,000 employees on food safety and wellness protocols. Currently a source of the outbreak has not been found.

“Chipotle has a zero-tolerance policy for any violations of our stringent food safety standards. We are committed to doing all we can to ensure it does not happen again.” – Brian Niccol, Chipotle

In line with the company’ zero-tolerance policy, some employees who worked at the Powell location were reportedly let go after the outbreak.

Chipotle has had several outbreaks that have made headlines over the last three years.