different populations (Käll, 2005). To address the possibility that the effect of NSEs can vary with the stage of epidemic, both Hurley et al. and MacDonald et al. analyzed cities where the initial measured seroprevalence among IDUs was less than 10 percent. In the Hurley et al. study, the authors did not find a significant association between NSE presence and the trajectory of the epidemic. However, MacDonald and colleagues did find a significant relationship: the mean annual weighted increase in HIV prevalence was 32.1 percent in cities that did not introduce NSEs, compared with a mean annual decrease of 7.8 percent in cities with NSEs (p=0.03).

Multiple studies show that NSEs do not reduce transmission of HCV, which has been attributed to the apparent failure of NSEs to provide enough ancillary injecting equipment such as sterile cotton, water, and alcohol wipes. While NSEs do reduce the frequency of reported needle and syringe sharing, they do not appear to reduce the sharing of other injecting equipment, such as cookers, cotton, rinse water, and drug solution (Hagan and Thiede, 2000; Sarkar et al., 2003; Taylor et al., 2000; Mansson et al., 2000). In contrast, a case-control study by Hagan et al. (1995) in Seattle found that NSE attendance was associated with a six-fold decrease in acquisition of hepatitis B virus (HBV), and a seven-fold decline in HCV acquisition. Given the high prevalence of HCV among IDUs, this represents an important area for future research.

Based on this evidence, the Committee concludes:

Conclusion 3-4: Four ecological studies have associated implementation or expansion of HIV prevention programs that include needle and syringe exchange with reduced prevalence of HIV in cities over time and after considering the local prevalence of HIV at the time of program implementation or expansion—although a causal link cannot be made based on these studies. The evidence of the effectiveness of NSE in reducing HIV prevalence is considered modest, based on the weakness of these study designs.

Conclusion 3-5: Moderate evidence indicates that multi-component HIV prevention programs that include needle and syringe exchange reduce intermediate HIV risk behavior. However, evidence regarding the effect of needle and syringe exchange on HIV incidence is limited and inconclusive.

Conclusion 3-6: Five studies provide moderate evidence that HIV prevention programs that include needle and syringe exchange have significantly less impact on transmission and acquisition of hepatitis C virus than on HIV, although one case-control study shows a dramatic decrease in HCV and HBV acquisition.

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