Chipotle Mexican Grill Inc said on Tuesday that an incident in which a number of Boston College students were sickened after eating at one of the burrito chain's restaurants in Boston appeared to be an isolated event.

"There are no reports of illness from any other restaurants, and the pattern here looks like norovirus isolated to one restaurant," Chipotle spokesman Chris Arnold told Reuters.

Health officials are investigating whether the 30 students were affected by E.coli. Chipotle has been linked to an E.coli outbreak in nine states, not including Massachusetts.

Chipotle shares were down 2.8 percent at $536.40.

(Reporting by Siddharth Cavale in Bengaluru; Editing by Ted Kerr)