NEW YORK (AP)--Chipotle's stock dropped in premarket trading Tuesday as the Mexican food chain continues to deal with fallout from an E. coli outbreak and contends with weakening sales.

A national outbreak of E. coli has been linked to Denver-based Chipotle, which has said that it is adopting stricter food safety standards. On Monday 30 Boston College students, including at least eight members of the men's basketball team, complained of gastrointestinal symptoms after eating at a Chipotle restaurant. The cause of those illnesses has yet to be confirmed. Chipotle said that there's no evidence to suggest the Boston incident is related to previous cases, noting that there's been no confirmed cases of E. coli connected to the restaurant operator in Massachusetts.

Aside from the E. coli troubles, Chipotle Mexican Grill Inc. has been experiencing a slowdown in its sales. Chipotle executives previously said that the chain's same-store sales growth would be more modest this year, as it's up against a tough year-ago comparison. The company is also raising prices to consumers to offset the higher cost of beef.

Shares of Chipotle declined $34.24, or 6.2 percent, to $517.51 about 90 minutes before the market open. At one point the stock was down more than 6 percent in premarket, its lowest point in more than a year.

--Associated Press