Four people accused of distributing a painkiller linked to the largest HIV outbreak in Indiana history have been arrested, and more arrests are expected, according to local and federal authorities.

Michael Elkins of Cartersville, Georgia, was arrested on June 16 in Clark County, a few miles north of Louisville, Kentucky, along with John Morgan, whose hometown wasn't available. The U.S. Drug Enforcement Administration says police searched the truck they were in and found about four ounces of methamphetamine, 19 Opana pills and an assault rifle.

DEA officials say Elkins had traveled to neighboring Scott County — where the outbreak is centered — numerous times over the last eight months to distribute methamphetamine, and that he obtained Opana in Alabama to distribute in Scott County, where the drug is being sold for as much as $160 per pill.

Indiana officials say needle-sharing among people injecting a liquefied form of Opana and other drugs has driven the HIV outbreak in southern Indiana. At least 170 people have tested positive for HIV this year in the region, mostly in Scott County, which typically sees only about five new HIV cases a year.

Two suspected couriers — Tyler Turner and William Thrower — were arrested four days later in the county with a half-pound of meth, according to the DEA. Their hometowns also weren't listed in court documents.

All four suspects are being held in the Clark County Jail on drug charges and $50,000 cash bond. Court documents don't list attorneys for any of the suspects, or indicate when they may appear in court.

Authorities say they expect additional arrests.