An E. coli outbreak linked to Chipotle Mexican Grill has spread to Maryland, the Centers for Disease Control and Prevention said Friday.

As of Friday, 52 people in nine states have become ill from what the CDC says are Shiga toxin-producing Escherichia coli O26 (STEC O26) infections. Twenty of those people have been hospitalized. No deaths have been reported. The newest cases of illness surfaced in Maryland, Illinois and Pennsylvania; one person in Maryland has been linked to the outbreak.

Of the three most recent illnesses reported in November, only one ill person reported eating at Chipotle Mexican Grill in the week before their illness began, the CDC says. "The epidemiologic evidence available at this time suggests that a common meal item or ingredient served at Chipotle Mexican Grill restaurants in several states is a likely source of this outbreak," the CDC said.

The E. coli outbreak started in the Northwest in October. As a result, Chipotle temporarily closed 43 of its restaurants in Washington and Oregon. Those restaurants have reopened. Cases have also been reported in New York, California and Ohio.

Illnesses that occurred after Oct. 31 might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported, which can take 2-3 weeks, the CDC says.

Chipotle says it has responded aggressively to the E. coli outbreak. The company is conducting food and environmental testing in affected restaurants and testing food in its distribution center.

"At this point no cause has been established between this issue and any ingredient," the company said on its website. If you became ill with diarrhea symptoms after eating at a Chipotle recently, you should contact a doctor, the CDC said.