"We found that in cities with NEPs HIV seroprevalence among injecting drug users decreased on average, whereas in cities without NEPs HIV seroprevalence increased. A plausible explanation for this difference is that the NEPs led to a reduction in HIV incidence among injecting drug users.
"NEPs have the potential to decrease directly HIV transmission by lowering the rate of needle sharing and the prevalence of HIV in needles available for reuse, as well as indirectly through activities such as bleach distribution, referrals to drug treatment centres, provision of condoms, and education about risk behaviour. Although these mechanisms have strong theoretical support, the published evidence for NEP effectiveness is limited. Previous studies of the effect of NEPs on HIV incidence used observational designs or statistical models.
"Observational designs included case studies; crosssectional, serial cross-sectional, and cohort studies (often without comparison groups); and case-control studies.4,5 Only one study assessed the impact of NEPs on HIV incidence. Des Jarlais and colleagues7 estimated that the hazard for incident HIV infection was 3·3 for injecting drug users in four high-seroprevalence cities without NEPs, compared with continuous users of NEPs in New York City. One case study investigated HIV prevention activities for five cities with low seroprevalence, but did not formally compare these with other cities that had high seroprevalence.13 The most frequently cited statistical model for assessment of NEP effectiveness was developed by the New Haven NEP evaluators, and is based on the theory that NEPs decrease HIV transmission rates by lowering the time that needles are in circulation.14
"The conclusion of a 1993 review by a University of California team' was that NEPs are associated with decreased HIV drug risk behaviour and are not associated with negative outcomes, but that there is no clear evidence that they decrease HIV infection rates.5 Few new data were available for the most recent US review by the Panel on Needle Exchange and Bleach Distribution Programs,4 which concluded that NEPs are effective, but acknowledged that the evidence was weak.
"Our study is distinguished from previous work by its worldwide scope and its design, which compares changes in HIV seroprevalence in cities with and without NEPs, rather than changes within a single city."
Hurley, Susan F., Damien J. Jolley, John M. Kaldor, "Effectiveness of Needle-Exchange Programmes for Prevention of HIV Infection," The Lancet, 1997; 349: 1797-1800, June 21, 1997.