Prevention of hepatitis C virus in injecting drug users: a narrow window of opportunity.

Human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infections remain major public health problems among injecting drug users (IDUs). In 2007, it was estimated that there were 15.9 million IDUs worldwide, with 3 million living with HIV [1]. While similar data are not available for HCV, given an HCV prevalence of 65% [2], it is estimated that 10 million active IDUs have been exposed to HCV and 8 million have chronic infection. The global burden of HCV is even greater in former IDUs. Implementation of harm reduction strategies since the early 1990s among many IDU populations led to decreases in HIV incidence or sustained low-level HIV prevalence and incidence [3]. In contrast, the impact on HCV transmission within the same populations has been much less pronounced [4]. This is likely related to the higher HCV prevalence among IDUs and higher risk of HCV infection following injection with a contaminated syringe (2.5%– 5.0% for HCV [5–8] vs .5%–2.0% for HIV [8–11]). High HCV incidence and rapidly increasing HCV prevalence are observed among young IDUs in different settings [12]. Factors associated with HCV acquisition include recent initiation to injecting [13, 14], unstable housing [15], female gender [16], ethnicity [17, 18], survival sex work [13, 19], frequent injecting cocaine use [13, 16, 20, 21], imprisonment [21], having a partner who injects [20], injecting networks [22], requiring help injecting [20], and borrowing injecting equipment [13]. The high risk of HCV among younger and recent IDUs indicates a narrow window of opportunity for prevention, with estimates of the median time to HCV infection of 3 years [14, 23]. Among long-term IDUs (injecting for .6 years), HCV prevalence (64%–94%) remains high [12]. It is clear that microenvironmental and macroenvironmental physical, social, economic, and political factors are important in shaping risk behaviors for HIV and HCV acquisition among IDUs [24]. Social network characteristics may be important and are associated with drug injection risk behaviors [25]. Network correlates of drug equipment sharing are multifactorial and include structural factors (network size, density, position, and turnover), compositional factors (network member characteristics and role and quality of relationships with members), and behavioral factors (injecting norms, patterns of drug use, and severity of drug dependency) [25]. In Seattle, Washington, a drug injecting network was highly connected, dense, and cyclic [26], and similar risk behaviors between injectors with and without recent HCV acquisition indicated that infection was associated with network position; that is, injecting with more individuals who happened to be HCV infected [26]. This is consistent with injecting network data from Melbourne, Australia, demonstrating that HCV infection is independently associated with the HCV status of network members [22]. Environmental social changes may also act as drivers of infection. In Australia, the estimated number of current IDUs between 1990 and 2000 doubled from 60,000 to 120,000, accompanied by a near doubling in the number of new HCV infections from 8,000 to 14,000 per year, despite widespread introduction and availability of harm reduction programs (eg, needle syringe programs [NSP] and opiate substitution treatment [OST]) from the early 1990s [27]. Subsequently, a dramatic reduction in the availability of heroin in Australia from 2001 onward resulted in a decline in the estimated number of IDUs and a decline in the estimated number of new HCV Received 5 November 2010; accepted 23 November 2010. Potential conflicts of interest: none reported. Reprints or correspondence: Jason Grebely, PhD, National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, CFI Building, Corner of Boundary and West Streets, Darlinghurst, Sydney NSW 2010, Australia ([email protected]). The Journal of Infectious Diseases 2011;203:571–574 The Author 2011. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals [email protected] 1537-6613/2011/2035-0001$15.00 DOI: 10.1093/infdis/jiq111