Epidemiology of Hepatitis C Virus: People Who Inject Drugs and Other Key Populations

Hepatitis C virus (HCV) infection is a serious public health problem, with globally 71 million people estimated to be chronically infected and at risk of long-term sequelae, including liver cirrhosis and hepatocellular carcinoma [1–3]. Acute infection is typically asymptomatic, and owing to HCV’s ability to evade the immune system, 70–80% of infections become chronic [4–6]. In those chronically infected, it may be decades after initial infection before significant sequelae develop. If left untreated, chronic liver disease will progress to cirrhosis in 5–20%, and 1–5% will die from decompensated cirrhosis or hepatocellular carcinoma [7]. HCV infection contributes to around 27% of liver cirrhosis cases and 25% of primary liver cancers, and resulted in an estimated 400,000 deaths worldwide from these complications in 2015 [1, 8]. Co-infections with HIV are an increasing problem in countries with HIV epidemics in people who inject drugs, and among men who have sex with men, and underlying viral hepatitis is becoming a major cause of death among people with HIV [1, 9].