HCV synthesis project: preliminary analyses of HCV prevalence in relation to age and duration of injection.

Early acquisition of hepatitis C virus (HCV) infection appears to affect a substantial proportion of injection drug users (IDUs)--between 20 percent and 90 percent. Analysing the range of HCV prevalence estimates in new injectors may help identify factors that can be modified to reduce HCV transmission. The HCV Synthesis Project is a meta-analysis of studies of HCV epidemiology and prevention in drug users worldwide. In this preliminary analysis, we examined data from 127 studies of IDUs that reported HCV prevalence in relation to age or year since onset of drug injection, analysing heterogeneity and calculating summary statistics where appropriate. Six studies reported gender-specific HCV prevalence rates among young or new injectors; the group mean prevalence was 47 percent for men and 44 percent for women (NS). Group mean age for HCV-negatives was 24.7 years (range 24-28) and 26.1 years (range 21-31) for HCV-positives (n=8 studies). Data were examined from 13 studies that compared HCV prevalence among young injectors to older injectors using 5-year age categories; substantial variation was present within these categories such that measures of central tendency were not calculated. Similarly, among studies reporting HCV prevalence among IDUs in relation to 1-year intervals of duration of injection (<1 year, <2 years, and <3 years), considerable variability was observed. Notably, there were studies in each category that reported prevalence of 70 percent or higher among recent-onset drug injectors. Our findings confirm previous studies reporting high risk of acquiring HCV shortly after onset of injection; thus, HCV prevention programmes must emphasize methods to reach new injectors. Future research should (1) report data on time to infection in depth, (2) provide detailed information on study methodology, and (3) characterize the research setting with respect to underlying factors that affect injection practices and networks. This will permit synthesis of a greater number of studies and may lead to the identification of factors that impede HCV transmission.