Hepatitis C spreads through contact with infected blood. The routes are not equally efficient, and how they are distributed between populations shapes who is affected and where.
Transmission
The most efficient route is direct percutaneous exposure. Sharing needles, syringes or other equipment used to prepare or inject drugs is the dominant route in many countries today, because injecting delivers the virus straight into the bloodstream.
Transfusion of infected blood or blood products was once a major route and remains one wherever donated blood is not screened; in countries with universal blood screening it has become rare. Reuse or inadequate sterilisation of medical equipment, especially syringes and needles in health-care settings, is another important route.
As a bloodborne disease, HCV can also pass from mother to child and sexually, but both routes are less efficient than blood exposure. Perinatal transmission occurs in roughly 5-6% of pregnancies in mothers with HCV, and the risk rises when the mother is also infected with HIV or carries a high viral load. Sexual transmission is inefficient, though it is more likely where sexual practices lead to blood exposure, such as among men who have sex with men or people with multiple partners. HCV is not spread through breast milk, food, water or casual contact such as hugging, kissing or sharing food and drinks.
Epidemiology
The distribution of infection differs between regions and populations. About 47 million people worldwide have chronic HCV infection, with roughly 0.9 million new infections and about 239,000 deaths each year, mostly from cirrhosis and hepatocellular carcinoma.
The prevalence of antibody to HCV increases from the north of Europe to the southern regions. It is higher in older people, because those born between the 1940s and the 1960s were infected through blood products before screening became routine. Today, where blood supplies are screened, most new infections occur among people who inject drugs and in closed settings such as prisons.