Chipotle Mexican Grill revealed today that the fast food chain was served with a grand jury subpoena last month in connection to the company’s first norovirus outbreak that occurred last August at one of their Simi Valley, CA locations.

The U.S. Food and Drug Administration’s office of criminal investigations and the California Central District leg of the U.S. attorney’s office are heading up the investigation, and Chipotle is fully cooperating. The subpoena, filed with the Securities and Exchange Commission, requires the fast food chain to hand over a “broad range of documents” related to last year’s first norovirus outbreak.

This investigation is focused on a completely separate event involving Chipotle. In December, a norovirus outbreak at a Chipotle restaurant near Boston College sickened more than 140 students.

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