(HealthDay News) — Addicts’ use of a powerful painkiller is driving a large HIV outbreak in Indiana, according to health officials.

Twenty-six new cases of HIV have been confirmed since mid-December, and there have been another four suspected cases. The outbreak is centered in five counties near Indiana’s border with Kentucky, CBS News reported.

Most of the cases are linked by addicts using tainted needles to inject the prescription opioid oxymorphone (Opana). Sexual transmission has been identified as the cause of some cases.

“We regularly investigate cases of HIV/AIDS, but this is the largest outbreak we have experienced,” said Amy Reel, of the state’s department of health, CBS News reported. “It’s also unique in that it’s primarily being transmitted through injection drug use,” she added.

Health Highlights: Feb. 26, 2015