The new cover of Businessweek is a Chipotle burrito. Vomiting

The new outbreak cases have been reported less than a week after Steve Ells, Founder and Co-Chief Executive at Chipotle, released a letter to apologize for outbreak that has sickened many people in different states. The company warned in an SEC filing earlier this month that business had been “extremely volatile” and it foresaw sales falling 8% to 11% in the fourth quarter.

Chipotle’s shares fell $27.40, or 5.3 percent, to close Tuesday at $494.61 in NY.

About 50 people fell ill in a nine-state outbreak of E. coli tied to the restaurants in October, and the Centers for Disease Control and Prevention has opened an investigation into a second possible outbreak in November. The Denver-based company had dropped 24 percent this year through Monday’s close, pulled lower primarily by the food-safety issues.

The same bacteria sickened 53 people in eight other states, and almost all who became ill say they ate at a Chipotle.

Williams noted that although the CDC can identify the location of restaurants that people ate in, Chipotle’s record-keeping is making it hard to “figure out what food is in common across all those restaurants”, the New York Times reports. Because it is not known if these infections are related to the larger, previously reported outbreak of E. coli O26 infections, these illnesses are not being included in the case count for that outbreak.

Dozens of Chipotle restaurants in Washington and OR were voluntarily closed after that outbreak.

Mansour Samadpour, head of IEH Laboratories, said after the restaurants reopened that the new procedures made Chipotle an industry leader. The cause of the E. coli contagion still hasn’t been found. “We are confident that we can achieve a level of food safety risk that is near zero”.

Chipotle says it is working on ways to better monitor the safety of the food ingredients it uses, including using methods such as high-resolution testing and additional food-safety training for employees.