At least six brokerages slashed their price targets on the burrito chain operator's stock on Thursday, a day after the company said it was served with a grand jury subpoena related to a probe into a norovirus incident at one of its restaurants.

Chipotle's stock, once a darling of Wall Street, lost a third of its value since the end of October, when an E. Coli outbreak linked to its restaurants was first reported.

The shares were down 1.6 percent at $420.02 on Thursday.

Chipotle's announcement on Wednesday highlighted deepening problems at the chain, which has been plagued by a spate of food-borne illnesses among other issues since October.

Last year started on a sour note for investors, when the company said it would not serve its popular "carnitas" at some restaurants after it found that a key supplier was not complying with its animal-welfare standards.

BTIG analysts on Thursday cut their price target by $134 to $530 and said the consistent negative news flow was keeping investors on the sidelines.

Analysts at Deutsche bank, who cut their price target to $400 from $480, said until Chipotle identified the source of the outbreak, fundamentals would continue to remain challenged.

Barclays cut its target to $465 from $540.

"Given the series of negative headlines and outsized media/social attention, we believe the time frame for a complete Chipotle recovery is extended," Barclays analysts wrote in a note.

Chipotle said on Wednesday it was further reducing its fourth-quarter same-store sales forecast, mainly due to media attention surrounding another norovirus incident at a Boston restaurant in December.

Despite all its problems, Wall Street analysts still have a largely positive outlook on the stock. Only two of the 34 analysts covering the stock have a "sell" rating. Thirteen recommend a "buy" or higher rating, while 19 a "neutral" recommendation.

While the median price target has fallen to $495 from $766 in the last 90 days, it is still well above the current stock price.

There were no changes in recommendations on Thursday.

(Reporting by Subrat Patnaik in Bengaluru; Editing by Saumyadeb Chakrabarty)