THE LANCET Summary

Background There have been no studies showing that participation in programmes which provide legal access to drug-injection equipment leads to individual-level protection against incident HIV infection. We have compared HIV incidence among injecting drug users participating in syringe-exchange programmes in New York City with that among non-participants. Methods We used meta-analytic techniques to combine HIV incidence data from injecting drug users in three studies: the Syringe Exchange Evaluation (n=280), in which multiple interviews and saliva samples were collected from participants at exchange sites; the Vaccine Preparedness Initiative cohort (n=133 continuing exchangers and 188 non-exchangers, in which participants were interviewed and tested for HIV every 3 months; and very-high-seroprevalence cities in the National AIDS Demonstration Research (NADR) programme (n=1029), in which street-recruited individuals were interviewed and tested for HIV every 6 months. In practice, participants in the NADR study had not used syringe exchanges. Findings HIV incidence among continuing exchange-users in the Syringe Exchange Evaluation was 1·58 per 100 person-years at risk (95 % CI 0·54, 4·65) and among continuing exchange-users in the Vaccine Preparedness Initiative it was 1·38 per 100 person-years at risk (0·23, 4·57). Incidence among non-users of the exchange in the Vaccine Preparedness Initiative was 5·26 per 100 person-years at risk (2·41, 11·49), and in the NADR cities, 6·23 per 100 person-years at risk (4·4, 8·6). In a pooled-data, multivariate proportional-hazards analysis, not using the exchanges was associated with a hazard ratio of 3·35 (95 % CI 1·29, 8·65) for incident HIV infection compared with using the exchanges. Interpretation We observed an individual-level protective effect against HIV infection associated with participation in a syringe-exchange programme. Sterile injection equipment should be legally provided to reduce the risk of HIV infection in persons who inject illicit drugs