Meta-analysis of hepatitis C seroconversion in relation to shared syringes and drug preparation equipment

Hepatitis C virus (HCV) infection is endemic among injection drug users (IDUs) [1], and is transmitted through shared injection syringes [2]. In addition, seroincidence studies have demonstrated transmission of HCV through the shared use of drug preparation equipment [3–6]. Estimation of infection risk is complicated by the frequent co-occurrence of sharing behaviors [7, 8]. A recent multi-site incidence study found that co-occurrence of sharing drug cookers, filtration cottons, rinse water, or of “backloading” (a syringe-mediated form of sharing prepared drugs) ranged from 86% to 96% [3]. In many IDU populations, syringe sharing has declined since HIV was first recognized, but shared use of drug preparation equipment has persisted, with 50–70% of IDUs reporting recent sharing of cookers or cotton, or backloading [3–6, 9–11]. Synthesizing knowledge on the relative risk of HCV infection associated with sharing behaviors, and estimating the relative importance of these behaviors is important, as it may be used to guide the development of more effective HCV prevention programs and information. Previous research syntheses of risk behaviors in regard to HCV acquisition have included an insufficient number of studies for quantitative analysis of distinct risk behaviors. One such synthesis grouped data from 10 studies regarding shared drug preparation equipment into a single meta-analysis [12]. Their analysis showed that risks associated with sharing drug preparation equipment generally ranged from 2.0 to 5.9, but that substantial heterogeneity precluded calculation of an overall effect. Heterogeneity of effects could have arisen for a number of reasons, including variability in the concentration of virus and amount of contaminated blood by equipment type. Such heterogeneity could be reduced by stratifying analyses by the specific type of equipment that was shared, but there were few studies included that reported effects with such detail. In this study, we examined the associations between shared syringes and drug preparation equipment with HCV seroconversion using data from the HCV Synthesis Project, a systematic review and meta-analysis of published and unpublished research studies of HCV epidemiology and prevention in drug users throughout the world [13]. Using pooled estimates, and data on the proportions of IDUs engaging in sharing behaviors, we calculated population attributable risk percentages reflecting the percentage of HCV seroconversions that could be prevented by eliminating specific sharing behaviors.