While heroin and prescription opioid abuse has been skyrocketing in suburban and rural areas of the U.S. in the last decade, needle exchanges and other “harm reduction” programs for drug users are far less available in these areas than in cities, according to a study published Thursday.

In the face of outbreaks of HIV among intravenous drug users in Indiana and elsewhere, scientists wanted to measure the availability in different states of needle and syringe exchanges, which have been shown to cut the transmission of HIV and hepatitis C.

Needle exchange programs allow intravenous drug users to drop off used needles and obtain sterile needles and syringes. By discouraging the use or sharing of dirty needles, the programs have been shown to slow the spread of HIV, the virus that causes AIDS.

Researchers from Mount Sinai’s Icahn School of Medicine in New York; the U.S. Centers for Disease Control and Prevention’s National Center for HIV/AIDS, Viral Hepatitis, SID and TB Prevention; and the North American Syringe Exchange Network in Tacoma, Washington issued a survey to the 204 needle exchange programs in the U.S.

Of the 75 percent of exchanges that responded, 69 percent were located in urban areas, 20 percent in rural areas and 9 percent in suburban areas.

In addition, only 37 percent of all needle and syringe exchanges located in rural areas were equipped with naloxone, a medication that can reverse the effect of opioid overdoses. That’s compared with 57 percent of exchanges in suburban areas and 61 percent of exchanges in urban areas.

The authors of the study, which was published online in the CDC’s Morbidity and Mortality Weekly Report, said that the “modest” number of rural and suburban exchanges — 20 and 14, respectively—raises the concern that many areas don’t have any access at all.

"Syringe service programs have been very effective in reducing HIV transmission in the U.S. and throughout the world," said Don Des Jarlais, a professor at Mount Sinai’s Icahn School of Medicine, and lead author of the study, in a release. "The biggest problem is simply that we do not have enough of them in rural and suburban areas."

For example, the authors found that there was only one needle and syringe exchange operating in the four-state region of Kentucky, Tennessee, Virginia and West Virginia. And they noted that, “large increases” in hepatitis C infections have been reported by the CDC in those four states between 2006 and 2012, largely connected to IV drug use.

Experts have warned that growing abuse of expensive prescription painkillers like Vicodin and OxyContin has created a new class of heroin users who switch over to the cheaper street drug and then get hooked. The result has been a national epidemic, with prescription drug overdoses now the leading cause of accidental death in the United States.

HIV infection among intravenous drug users dropped by 80 percent between 1990 and 2006, according to the CDC. But the uptake of IV drug use has been particularly concentrated in suburban and rural areas. That has been linked to outbreaks of hepatitis C and HIV.

In March, Indiana authorized a short-term needle exchange program via emergency order to head off an HIV outbreak that has infected 184 people in rural parts of the state, largely tied to IV drug use.

And several states including California, New York, North Carolina, Kentucky, Ohio and Vermont have relaxed restrictions on naloxone, allowing laypeople and first responders to carry it by prescription or standing order at health clinics and needle exchanges. The New York City Police Department moved to equip nearly 20,000 of its officers with naloxone kits in 2014.

Some 34 U.S. states and the District of Columbia have needle and syringe exchanges, according to amFar, the Foundation for AIDS Research, but such programs are banned from using federal funding.