Police say a mass overdose at a house in Chico that killed one man and left four people in critical condition appears to have been largely caused by the unsafe opiate fentanyl, the Enterprise Record reports.
"Unfortunately one male individual was pronounced dead at the scene", O'Brien said, adding that the residence where the overdose occurred is being treated as a hazmat site.
A mass fentanyl overdose incident in Northern California on Saturday left one dead and at least a dozen others hospitalized.
The conditions of the non-critical victims were not released, and the person who died was not identified. Pacific time on Saturday at a home in Chico, said Chico Police Chief Mike O'Brien. Authorities suspect the overdoses were caused by ingestion of the risky drug and a separate substance that is yet to be determined.
A relationship between the victims has not been established, though police say they all knew each other to some extent.
And the drug was so strong, two police officers, who were responding to the emergency call, also became sick after coming onto contact with the victims.
Chico Fire Department Division Chief Jesse Alexander told the station it was the largest mass casualty incident he had seen in years.
Officers administered CPR and six doses of Naloxone, an opioid-reversal drug, when they arrived on the scene. It has not been confirmed, but police say signs point to poisoning from fentanyl, an opioid often mixed with heroin or cocaine.
Police officers in Chico County carry Naloxone, a medicine used to reverse overdoses, which they gave to the surviving victims.
The home is now being treated as a "hazmat site", but O'Brien said it is "not a danger to the public".
Fentanyl, a synthetic opioid pain reliever, is 50 to 100 times more potent than morphine.
In November, a new report from the Centers for Disease Control and Prevention (CDC) found that fentanyl was behind the increase of drug overdose deaths between 2016 and 2017. "That is changing unfortunately. and now we've have this MCI (mass casualty incident)...that concerns us all".