AUSTIN, Texas (AP) — Authorities in Texas are investigating at least nine deaths this week in connection with an unusual spike of opioid overdoses in Austin that health officials are calling the city’s worst overdose outbreak in nearly a decade.

Emergency responders in the Texas capital typically field only two to three calls per day, said Steve White, assistant chief of the Austin-Travis County Emergency Medical Service. But at least 65 people required overdose treatment between Monday and Wednesday, said Darren Noak, a spokesman for the agency.

“At this time, it is apparent that there is an deadly batch of illicit narcotics in our community,” Austin Police Department Assistant Chief Eric Fitzgerald said at a news conference Tuesday.

Preliminary testing showed that all nine people who died had traces of fentanyl in their system and the majority had other drugs present too, according to Travis County spokesman Hector Nieto.