DENVER — Health officials in Ohio released their findings on Aug. 16 regarding the recent foodborne illness outbreak at a Chipotle Mexican Grill restaurant in Powell, Ohio that sickened 647 people.

The Delaware General Health District said that stool samples collected in July tested positive for the toxin that Clostridium perfringens forms in the gastrointestinal tract. The food samples did test negative for C. perfringens bacteria.

A specific food has not been identified as the source for the illness, Delaware Health said. The Centers for Disease Control and Prevention (C.D.C.) is still carrying out other tests at its lab.

In response to the news, Chipotle chief executive officer Brian Niccol released a statement regarding the outbreak. 

“Chipotle 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,” Mr. Niccol said. “Once we identified this incident, we acted quickly to close the Powell restaurant and implemented our food safety response protocols that include total replacement of all food inventory and complete cleaning and sanitization of the restaurant.”

Additionally, Mr. Niccol said, the company will retrain all restaurant employees nationwide starting next week on food safety and wellness protocols.

“To ensure consistent food safety execution, we will be adding to our daily food safety routines a recurring employee knowledge assessment of our rigorous food safety standards,” he said.

Chipotle is still recovering its image from the foodborne illness outbreak of late 2015 that included several cases of E. coli O26 across 11 states followed by the discovery of norovirus at a Boston-based restaurant that reportedly sickened 80 customers.