Chipotle Mexican Grill Inc. received a subpoena in connection with a criminal investigation into an outbreak of norovirus at a Simi Valley restaurant.

The Denver fast casual chain said in a filing Wednesday with the Securities and Exchange Commission that the subpoena from the U.S. District Court for the Central District of California received in December was for a “broad range” of documents related to the norovirus incident from August of last year.

The federal court is conducting the investigation in conjunction with the Food and Drug Administration’s Office of Criminal Investigations.

“We intend to fully cooperate in the investigation,” the company stated in the filing. “It is not possible at this time to determine whether we will incur, or to reasonably estimate the amount of, any fines, penalties or further liabilities in connection with the investigation pursuant to which the subpoena was issued.”

Norovirus is a contagious virus that causes the stomach or intestines or both to become inflamed. It is spread from an infected person, contaminated food or water, or by touching contaminated surfaces. Each year, it causes 19 million to 21 million illnesses and contributes to 570 to 800 deaths, according to the Centers for Disease Control and Prevention.

An outbreak of norovirus and E. coli bacteria at Chipotle locations in several states has impacted sales, which were down 30 percent in December, according to the SEC filing.

In November, the chain temporarily closed restaurants in Oregon and Washington State. A separate incident in Massachusetts in December resulted in more than 100 Boston College students becoming ill.

Also, the CDC is investigating an outbreak of E. coli at Chipotle restaurants in nine states. E. coli is a bacteria found in the human intestinal tract. Some forms are pathogenic that can cause intestinal and respiratory illnesses.