In just five years, the number of new hepatitis C virus (HCV) cases reported to U.S. health authorities has nearly tripled, recently reaching a 15-year high, according to preliminary surveillance data released last week by the Centers for Disease Control and Prevention (CDC).

Specifically, the report shows that in 2015, the number of acute hepatitis C cases reported to the CDC’s National Notifiable Diseases Surveillance System (NNDSS) reached a total of 2,436 infections—a 2.9-fold increase from the 850 cases reported in 2010. But the CDC also estimates that owing to underreporting, the number of new hepatitis C infections was actually nearly 34,000 in 2015.

According to the report, new hepatitis C infections appear to be increasing most rapidly among young people ages 20 to 29 years old. The CDC says increasing injection drug use associated with the country’s ongoing opioid epidemic is largely to blame.

“We must reach the hardest-hit communities with a range of prevention and treatment services that can diagnose people with hepatitis C and link them to treatment,” said Jonathan Mermin, MD, director of the CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention in a press release about the findings.

The report also recommends a variety of comprehensive approaches to combat the country’s dual epidemics of opioid addiction and hepatitis C, including improving access to addiction treatment and recovery services, strengthening public health surveillance initiatives and supporting syringe exchange programs across the country. 

The CDC data also show that the majority (nearly three fourths) of the 3.5 million Americans estimated to be living with hepatitis C are baby boomers born between 1945 and 1965. Even with the influx of new injection-related infections, baby boomers remain nearly six times more likely to be living with hepatitis C than those in other generations and are also at a much greater risk of dying from the virus.

The CDC also notes that while new hepatitis C treatments can cure an infection in as little as two to three months, many Americans are still not able to get them. In 2015, nearly 20,000 people died from HCV-related causes, and the majority of those who died were age 55 and older.