Effectiveness of needle-exchange programmes for prevention of HIV infection.

BACKGROUND: Needle-exchange programmes (NEPs) are potentially a key strategy for containing the spread of HIV infection among injecting drug users, but their implementation has been limited by uncertainty about their effectiveness. We used an ecological study design to compare changes over time in HIV seroprevalence in injecting drug users worldwide, for cities with and without NEPs.
METHODS: Published reports of HIV seroprevalence in injecting drug users were identified, and unpublished information on HIV seroprevalence for injecting drug users entering drug treatment in the USA between 1988 and 1993 was obtained from the Centers for Disease Control and Prevention. Details of the implementation of NEPs were obtained from published reports and experts. For each of the 81 cities with HIV seroprevalence data from more than 1 year and NEP implementation details, the rate of change of seroprevalence was estimated by regression analysis. The average difference in this rate for cities with and without NEPs was calculated.
FINDINGS: On average, seroprevalence increased by 5.9% per year in the 52 cities without NEPs, and decreased by 5.8% per year in the 29 cities with NEPs. The average annual change in seroprevalence was 11% lower in cities with NEPs (95% CI -17.6 to -3.9, p = 0.004).
INTERPRETATION: A plausible explanation for this difference is that NEPs led to a reduction in HIV incidence among injecting drug users. Despite the possibility of confounding, our results, together with the clear theoretical mechanisms by which NEPs could reduce HIV incidence, strongly support the view that NEPs are effective.