NEW YORK (AP) — The Centers for Disease Control and Prevention says it is investigating more recent cases 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 says five people have been reported sick in the new outbreak, including one in Kansas, one in North Dakota and three in Oklahoma. It said Monday those illnesses started between Nov. 18 and Nov. 26, and that all five people said they ate at a Chipotle the week before they got sick.

For the larger outbreak, 53 people had been reported sick, with 46 of them saying they ate at a Chipotle. The most recent illness linked to Chipotle among those started Nov. 10.

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

The CDC has not identified the ingredient that made people in the larger outbreak, which has already scared customers away and caused Chipotle's sales to plummet. Chipotle co-CEO Steve Ells has told The Associated Press he doesn't think the company will ever know for sure the exact ingredient that was responsible, but that he believes it was bacteria in fresh food like tomatoes or cilantro.

Following the outbreak, Chipotle Mexican Grill Inc. has said it is implementing new standards to ensure food safety. Spokesman Chris Arnold said in an email Monday that the chain is in the process of implementing those programs, which include increased testing and food safety training for workers.

The more recent cases are the latest blow for Chipotle, which also closed a restaurant in Boston earlier this month after more than 140 students at Boston College reported feeling gastrointestinal symptoms. Those cases were linked to norovirus, and Chipotle has said they were unrelated to the E. coli outbreak.