MIAMI: The number of hepatitis C infections have nearly tripled in the United States in the last five years, particularly among people in their 20s, researchers said Thursday. Hepatitis C is the top infectious disease killer in the nation, taking nearly 20,000 lives in 2015, said the Centers for Disease Control and Prevention. Experts say the rise of the opioid epidemic, with increasing numbers of people sharing needles to inject heroin and prescription painkillers, is driving the increase in cases. People with hepatitis C often have no symptoms, so they are unaware of their infection. The CDC said the number of new cases reported to the federal agency was 850 in 2010, and rose to 2,436 cases in 2015.