The U.S. Centers for Disease Control and Prevention (CDC) said on Monday it was looking into a new, more recent outbreak of a different strain of E.Coli linked to the burrito chain.

The news as Chipotle is still grappling with the sales and public relations fallout from an earlier outbreak of the bacteria in the autumn that affected 53 people who’d eaten at its restaurants in nine states. Sales have plummeted, dragging down the one-time Wall Street darling’s shares with them. Last week, the company took out full-page ads in several major newspapers, including the Wall Street Journal, to apologize while founder and CEO Steve Ells took to the airwaves in a bid to contain the damage.

Though the CDC said it does not know whether the two outbreaks are related, Chipotle believes they are and said it is helping the CDC and the Food and Drug Administration with their investigation.

The CDC said it was looking at different, rare DNA fingerprint of Shiga toxin-producing E. coli O26 (STEC O26) linked to Chipotle Mexican Grill. The agency said that five people have been reported ill in Kansas, North Dakota and Oklahoma, with all five saying they ate at a Chipotle in the week before they took ill, with dates ranging from November 18 and November 26.

As for the initial outbreak, the CDC said there was one new case of illness reported.

“We have indicated before that we expected that we may see additional cases stemming from this,” Chipotle spokesperson Chris Arnold, said in an email to Fortune.

Chipotle has finished a complete reassessment of its food safety program and is implementing changes as a result, Arnold said. Those efforts include high resolution testing of ingredients, end of shelf-life testing of ingredients, continuous improvement in the supply system based on testing data, and enhanced food safety training for all restaurant workers.

“With all of these programs in place, we are confident that we can achieve a level of food safety risk that is near zero,” Arnold wrote.