ST. PAUL — After years of running Minnesota’s largest needle exchange, Brian Warden is beginning to see something new among the increasing numbers of suburban and rural heroin users coming to trade in used needles.

“What strikes me about it is they don’t seem to have had what’s traditionally called the gateway effect,” Warden said from his office at Minnesota AIDS Project’s Mainline exchange in Minneapolis. “I had a client here last week who has never smoked a cigarette, never smoked a joint, never taken a pill, she says, yet she knows how to shoot heroin.”

As communities across the state continue to struggle with rising rates of heroin abuse, these users, who are also younger, seem to be contracting the potentially liver-destroying disease hepatitis C at higher rates, according to state data. And health officials suspect dirty needles may be to blame.

Minnesota’s situation mirrors what’s happening in other states with booming heroin rates, from Massachusetts to Wisconsin, and it’s leading to what a report from the U.S. Department of Health and Human Services described as an “emerging epidemic” of hepatitis C.

Hepatitis C is the most common blood-borne pathogen nationally. At least 3.9 million Americans live with chronic hepatitis C, according to the federal Centers for Disease Control and Prevention.

Kristin Sweet, an epidemiologist at the Minnesota Department of Health, says it’s difficult to determine exactly how many people carry the virus. In 2012, 32 Minnesotans were newly diagnosed with hepatitis C. Sweet said the number of people being diagnosed with hepatitis C tends to lag behind the actual numbers of people contracting the disease because many people develop no symptoms and therefore aren’t tested.

There is no vaccine for hepatitis C. Treatment of acute hepatitis C can reduce the possibility that the condition becomes chronic. But that’s only if it’s diagnosed.

“People generally don’t know they have it unless they’ve been tested for it,” Sweet told Minnesota Public Radio. “Some people develop symptoms of infection, those people are more likely to go in and get tested, but since not everyone has symptoms, not everyone will go in and get tested for it.”

State data show young people make up an increasing share of new diagnoses. In 2001, only about 5 percent of new cases were in people under 30, but in 2012 that had risen to 13.5 percent.

“Certainly, hepatitis C is transmitted through injection drug use, so people who inject drugs are at high risk of getting hepatitis C,” Sweet said. “If we see increases in injection drug use, it makes sense that we’d see hepatitis C as well.”

Other states also have seen more young people being diagnosed with the disease.

A 2010 study in Massachusetts found that people between the ages of 15-24 were contracting hepatitis C at higher rates than in the past. Further studies in states like Wisconsin and Pennsylvania showed “rising rates of hepatitis C infection among young injectors, both male and female, primarily white, found in suburban and rural settings.”