Needle-sharing among people injecting the extended-release opioid Opana led to the spread of HIV in Indiana last year, according to a report in the New England Journal of Medicine.

Health officials in Scott County, Indiana, reported 181 HIV infections between November 2014 and November 2015, HealthDay reports.

“It was the largest outbreak that has occurred in the U.S. since the introduction of HIV treatment,” said lead author Dr. Philip Peters of the Division of HIV/AIDS Prevention at the U.S. Centers for Disease Control and Prevention. “And it occurred in a poor and rural community. We have not seen HIV outbreaks in these types of communities before.”