LOS ANGELES (Reuters) - Thirty Boston College students got sick after eating at Chipotle Mexican Grill CMG.N over the weekend, a school spokesman said, sending company shares down 6 percent in extended trading on Monday on fears of more food poisoning problems at the burrito chain.

A Chipotle restaurant is shown in Federal Way, Washington in this November 20, 2015 file photo. REUTERS/David Ryder/Files

Chipotle said it had temporarily closed its restaurant in Boston’s Cleveland Circle, where a college spokesman said all the students reported eating, while it works with local health officials to investigate the illnesses.

The sickened students included members of the Boston College men’s basketball team, spokesman Jack Dunn said.

The Massachusetts Department of Public Health received more than 20 reports of illness from Boston College students and is working to determine if they are tied to a Chipotle-linked outbreak of E. coli, spokesman Scott Zoback said.

Federal health investigators said on Friday the E. coli outbreak had expanded to nine states, with 47 of the 52 people sickened having reported eating at the chain.

“We do not have any evidence to suggest that this incident is related to the previous E. coli incident,” Chipotle spokesman Chris Arnold said in an email. “There are no confirmed cases of E. coli connected to Chipotle in Massachusetts.”

Boston College officials sent alerts on Monday to students, informing them of the suspected food poisoning.

The time between ingesting E. coli bacteria and feeling sick is usually three to four days, but may be as short as one day or as long as 10 days, according to the U.S. Centers for Disease Control and Prevention. Symptoms often begin slowly with mild belly pain or non-bloody diarrhea that worsens over several days.

The Chipotle outbreak was first identified in Seattle and Portland, Oregon, and the company temporarily closed all 43 of its restaurants in those markets on Oct. 31.

The states with reported cases are Illinois, Maryland, Pennsylvania, California, Minnesota, New York, Ohio, in addition to Oregon and Washington. People in those states were sickened between mid-October and mid-November.

Chipotle warned on Friday that the outbreak was expected to cause this quarter’s sales at established restaurants to fall for the first time in company history. It also said sales could be battered by additional reports of illness.

Chipotle shares were down 6.4 percent to $516.61. Before the reports of illness, shares traded at nearly $650.