Reports of new hepatitis C infections in the United States nearly tripled over five years, reaching a 15-year high, federal government data show.

The highest number of new infections were reported among 20- to 29-year-olds. Many stemmed from the growing use of injected drugs linked to the current opioid epidemic, officials said.

The number of reported cases rose from 850 in 2010 to 2,436 in 2015, according to the U.S. Centers for Disease Control and Prevention.

But nearly half of people who have the liver infection don't know it, so most new cases are never reported. The CDC estimated there were actually about 34,000 new hepatitis C infections nationwide in 2015.

"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. This wide range of services can also prevent the misuse of prescription drugs and ultimately stop drug use -- which can also prevent others from getting hepatitis C in the first place," said Dr. Jonathan Mermin in a CDC news release.

He is director of the agency's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention.

The virus can be spread by sharing drugs and needles, the stick of a contaminated needle, and through sex. A child can also catch it if born to an infected mother.

More Americans die from hepatitis C than any other infectious disease reported to the CDC. Nearly 20,000 Americans died from hepatitis C-related causes in 2015, and most were age 55 and older, according to the new report.

Three-quarters of the 3.5 million Americans infected with hepatitis C are baby boomers, born between 1945 and 1965. They are six times more likely to be infected than people in other age groups and have a much higher risk of death from the virus, the CDC said.

Recent CDC studies also show that hepatitis C infections are rising among women of childbearing age, putting a new generation at risk.

New medicines can cure hepatitis C in as little as two to three months, but many people who need treatment can't get it, according to the CDC.

"Stopping hepatitis C will eliminate an enormous disease and economic burden for all Americans," said Dr. John Ward, director of CDC's Division of Viral Hepatitis.

"We have a cure for this disease and the tools to prevent new infections. Now we need a substantial, focused and concerted national effort to implement the National Viral Hepatitis Action Plan and make effective prevention tools and curative treatment available to Americans in need," Ward said.

The federal action plan sets goals for improving prevention, care and treatment of viral hepatitis and eliminating new infections.