This issue of Hot Topics in Viral Hepatitis is the first one of a series devoted to the transmission of the hepatitis C virus (HCV) infection. The first 4 articles discuss the transmission of HCV in the health care setting (both patients and health care workers), between sexual partners and in the community of injection drug users. All the articles are written by leading experts with specific expertise in public health issues.

An adequate appraisal of HCV transmission routes has 2 major benefits. First, molecular tracing of the worldwide HCV epidemic over the past decades may help in the effort to predict regional patterns of clinically significant endpoints, such as mortality due to hepatocellular carcinoma. Second, an assessment of the relative contribution of the different risk factors of transmission is a prerequisite to the implementation of targeted preventive measures.

Until the 1980s, the major route of HCV transmission in the developed world was iatrogenic, via blood transfusions and unsafe and invasive medical procedures. Today, with the introduction of screening procedures, blood transfusions have reached an unprecedented level of safety: the current risk of acquiring transfusion-transmitted HCV is less than 1 case per million blood units. In developed countries, iatrogenic transmission of blood-borne pathogens is likewise very rare and confined to situations where breaches in safety guidelines have occurred. However, the situation is completely different in many other countries. There, contaminated blood transfusions and the reuse of infected medical equipment remain an important mode of HCV transmission. The combination of limited resources, poorly educated health care workers and cultural prejudice all contribute to the spread of blood-borne agents such as HCV.

Among the other modes of transmission discussed in this issue, paraphernalia-sharing by injection drug users is now the main source of HCV infection in western countries, and is spreading at dramatic speed in many emerging countries. Finally, the risk of acquiring HCV via sexual intercourse or through participation in various health care professions has been scaled down, although the role of certain practices should not be overlooked when counseling individuals at risk.

As a result of the changing epidemiology of HCV in different regions of the world, Harvey J. Alter has correctly observed that "HCV infection is now a disease of two worlds". In the absence of a vaccine offering complete protection, we must emphasize prevention through education in every intervention. Countries with developed and resource-rich health care systems are the leading players in this global task.