Local health officials in Ohio confirmed the cause of a Chipotle food safety outbreak that sickened more than 600 people between July 26 and July 30. In response, the brand said it would retrain all restaurant employees on food safety procedures starting next week, with the daily routine augmented. Chipotle isn’t planning to close any stores and will add a recurring online employee assessment for food safety standards, according to Reuters.

“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. 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,” CEO Brian Niccol said in a statement.

An emailed statement per BuzzFeed News added: “While this incident impacted only one restaurant, Chipotle Field Leadership will be retraining all restaurant employees nationwide beginning 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. Additionally, the health department did not identify the food source. And for training, we are retraining all employees next week during their shifts on our top food safety priorities. We are not closing the restaurants. Then to ensure ongoing execution and compliance, we are adding to our food safety routines a recurring online employee knowledge assessment of our food safety standards.”

The Delaware General Health District said August 16 that food samples tested from a Powell, Ohio, store came back negative for clostridium perfringens, but stool samples returned positive for the toxin it forms. The bacterium often infects food prepared in large quantities and kept warm for a long time. Health district official Traci Whittaker said five of six stool samples came back positive. The district, however, could not specify a certain food as the source, and the Centers for Diseases Control and Prevention are conducting further tests.

Officials said 647 people self-reported gastrointestinal symptoms after eating at the Chipotle, which closed July 30 before reopening the next day. Customers reported food poisoning and diarrhea after eating tacos and burrito bowls. Illnesses resulting from clostridium perfringens affect nearly 1 million people per year, according to the CDC. The recovery is typically a day or two and the infection doesn’t spread from one person to another.

Chipotle’s stock was trading down a touch over 4 percent early Thursday afternoon. It hit a two-year high earlier in the day after being upgraded by Morgan Stanley. The firm raised Chipotle’s 12-month price target to $600 per share, a sizable 21 percent upside from Tuesday’s closing price of $493.32 per share.

Morgan Stanley analyst John Glass said a change in management and “an incentive plan designed to deliver the bull case in earnings,” as well as “plenty of low hanging opportunities in marketing, product development, and operational initiatives to drive sales,” were supplying credence to Chipotle’s comeback efforts.

Chipotle’s same-store sales surged 3.3 percent in the second quarter. Revenue lifted 8 percent to 2.4 billion.

Here are some of the changes Chipotle’s making to keep the momentum going.

Food safety, of course, will be a critical element of Niccol’s tenure at Chipotle. The company’s 2015 E. coli 14-state outbreak continues to linger, and Chipotle dealt with a Sterling, Virginia, norovirus incident last summer that sent its stock on a nosedive. Moves like adding bacon to its menu, and increased digital efforts, executives hope, can help the fast casual shift the narrative. 

Fast Casual, Food Safety, Story, Chipotle