NEW YORK – The Centers for Disease Control and Prevention said Monday it is investigating a more recent batch of E. coli cases linked to Chipotle, and that it does not know yet if they are linked to a larger outbreak that began in October.

So far, the agency said five people have been reported sick in the new outbreak, with illnesses starting between Nov. 18 and Nov. 26. They include one person in Kansas, one in North Dakota and three in Oklahoma. All five said they ate at a Chipotle the week before they got sick. The North Dakotan had traveled to Kansas and ate at the same Chipotle location as the Kansas resident who fell ill.

The development is the latest bad news for Chipotle Mexican Grill Inc., which saw its sales plummet after the emergence of the larger E. coli outbreak that has sickened 53 people in nine states. The most recent illness linked to Chipotle among those cases started Nov. 10.

Each year, about 48 million people get sick from foodborne illnesses, according to the CDC.

Following the outbreak, Chipotle Mexican Grill Inc. assured customers that it would tighten its food safety standards. Spokesman Chris Arnold said in an email Monday that the chain is in the process of implementing its new programs, which include increased testing of ingredients and training for workers. He noted that even the most recent exposures reported by the CDC are now a month old.

“We have indicated before that we expected that we may see additional cases stemming from this, and CDC is now reporting some additional cases,” Arnold wrote.