Since the discovery of hepatitis C virus (HCV) in 1989, hundreds of studies and surveys have been conducted to characterize its occurrence in drug users. Several features of HCV epidemiology have been resolved, including its hyper-endemicity in injection drug users (IDUs), and its resistance to control by public health prevention programs. Since there has been so much HCV research in recent years, new questions have arisen - how to synthesize what is known, explain inconsistencies, find similarities, and determine what is still unknown. A meta-analysis is needed at this stage to reconcile contradictory research findings regarding factors that may influence transmission; the length of the period of susceptibility to HCV, when prevention can occur; the extent of HCV infection in those who smoke or sniff drugs; and the magnitude and future course of HIV/HCV co-infection in IDUs. We estimate that 800-1000 data reports (published articles, unpublished manuscripts, abstracts, presentations, and other reports) will be available for analysis in this study, to systematically address these specific aims: 1. Summarize HCV epidemiology and prevention in injection and other drug users in relation to person, place and time, using data from the US and abroad. 2. Examine whether observed HCV incidence and prevalence, and measures of association vary in relation to research methodology, such as study design, sampling method or length of follow-up. 3. Describe variation in HCV prevalence among HIV-positive IDUs in relation to characteristics of the population, the setting, or time period of the study. 4. Describe the state of research on HCV in drug users in terms of the number of studies completed or underway, the scope of their investigation, and other factors that suggest research gaps. HCV is the cause of a substantial burden of disease, disability and death in drug users and others, and in many regions of the world, IDUs are the primary reservoir of HCV in the community. Public health policy related to preventing HCV transmission, meeting the demand for medical management of HCV and HIV/HCV co-infection, and setting the HCV research agenda would be guided by the accomplishment of these aims.
