Hot off the heels of its last run-in with E. coli, Chipotle Mexican Grill is being investigated yet again for a series of outbreaks traced to its restaurants in multiple states.

According to the Centers for Disease Control and Prevention, which announced their most recent probe on Monday, five people were found with a strain of E. coli between November 18 and 26 in Kansas, North Dakota, and Oklahoma. All of those that fell ill reported eating at the popular fast-casual chain about a week beforehand.

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The strain of the Shiga toxin-producing Escherichia coli026 is rare, according to the CDC. The most recent cases were being treated separately from another recent E. coli scare at the chain.

Beginning in October, some 46 people in nine states who said they ate at a Chipotle were infected with E. coli. Initial reports put the number of cases in the 50s, though more sensitive testing measures reduced that number, according to a company release.

In a separate incident earlier this month, more than 140 Boston College students fell ill with norovirus after eating at a branch. Following the outbreak, founder and CEO Steve Ells reassured customers, telling NBC that “The procedures we’re putting in place to eat are so above industry norms that we are going to be the safest place to eat.”

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The E. coli scares had dinged the company's stocks already. But following the investigation announcement on Monday, Chipotle's shares dropped more than 4 percent on Tuesday, CNBC reported.

"I will say though, that we can assure you that there is no E. coli in Chipotle," Ells told CNBC last week. "We have thoroughly tested our food, we have thoroughly tested our surfaces and we are confident that Chipotle is a safe place to eat."