impact of needle and syringe program coverage on hiv incidence in people who inject drugs

Background: the sharing of syringes by people who inject drugs (pwid) is an important factor for the transmission of hiv. needle and syringe programs (nsp) are widely used to reduce any harm associated with drug injection, however since the impact of these programs have not been systematically studied our objective is to model the impact of nsps on hiv incidences for pwid in kermanshah, iran. objectives: the aim of this study was to determine the effectiveness of nsp coverage in prevention of hiv incidence among pwids. patients and methods: we used wilson et al.’s mathematical model to predict the occurrence of hiv amongst pwid with sufficient and insufficient client-level coverage of nsps. we parameterized and calibrated the model using behavioral and epidemiological data collected in an empirical study of 470 active pwid and recruited them through two drop-in centers (dic) in kermanshah, iran from april to september, 2014. other parameters such as risk of hiv transmission through injection with a shared injection, and effectiveness of syringe cleaning were obtained from the literature. we applied monte carlo simulation (10,000 runs) to capture the uncertainty (simulation interval – si) in the model’s output. results: given the output of the model, we found that among the pwid with sufficient coverage of nsps the hiv rate is 1.02%, while those with insufficient coverage is increased to 4.04% (risk different = 3%, si 95% 2.7 - 3.4%). by reducing the percentage of sharing from 18% (in patients with insufficient nsps coverage) to 10%, the hiv incidence will be dropped to 0.9% (si 95%, 0.4 - 1.3%). conclusions: we found a large impact due to nsps for reducing the occurance of hiv among active drug injectors who have been provided sufficient needles and syringes. the coverage of nsps needs to be increased to observe such significant impact.