importance of the social context of injecting

Injecting drug users (IDUs) are at high risk of hepatitis C (HCV) infection.1,2 In studies examining the prevalence of HCV in populations of IDUs, duration of injecting and the frequency of injecting each day are the factors most consistently associated with infection.3–13 Numerous studies measuring the incidence of HCV infection among IDUs have found that increased frequency of injecting is associated with seroconversion.9,14–16 Overall, this body of research confirms that an IDU’s risk of exposure to HCV increases as his or her number of lifetime injecting episodes increases.17 Injecting drugs does not in itself cause HCV infection. It is engagement in unsafe injecting practices which permits the parenteral spread of this virus. Specific injecting practices such as borrowing used syringes from other IDUs (recipient syringe sharing), backloading, and the sharing of ‘cookers ’ and filters constitute unsafe injecting practices. (Backloading involves the preparation of heroin in one syringe and subsequent transfer of half the contents to a different syringe.) Many studies have demonstrated an association between these practices and HCV infection.3–6,15 It has been proposed that engagement in these specific overt risk behaviours is the principal contributor to an individual’s risk of HCV infection.1 If this assertion is correct, accurate measurement of unsafe injecting episodes shoul