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.

The victims ranged in age from 30s to 50s and spanned diverse ethnic backgrounds, said Keith Pinckard, Travis County’s chief medical examiner. Police say two people have been detained during the investigation but no charges related to overdoses had been filed as of Wednesday.

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Fitzgerald said officers administered an overdose-reversing drug, naloxone, at the scene of several cases as they awaited emergency services. He added that citizen bystanders in some cases stepped in to administer the life-saving drug themselves, and thanked them for intervening.

According to Travis County Judge Andy Brown, the county’s top elected official, kits for administering overdose antidote drug naloxone during emergency situations were distributed to locals in affected areas and training was provided by emergency personnel for those willing to carry the medication.

Brown said that the drug, which combats overdoses, had previously been proactively distributed across the area through city and county programs that attempt to fight increasing opioid overdoses. He said the efforts are conducted in coordination with local groups that often respond to overdose crisis.

It is the largest overdose outbreak in Austin since a synthetic drug referred to as K2 was distributed locally in 2015, Brown said.