Human immunodeficiency virus (HIV) infection in parenteral drug users: evolution of the epidemic over 10 years

Background Evaluation of acquired immunodefidency syndrome (AIDS) preventio n strategies requires an on-going follow up of the frequency of human immun odeficiency virus (HIV-1) infection. The aim of this study was to examine t he trends in prevalence and incidence of HIV-1 infection among injecting dr ug users (IDU) during the period 1987-1996. Methods Transversal and cohort studies were designed which included a conse cutive sample of 7132 IDU who attended three AIDS Prevention and Informatio n Centres in the Region of Valencia (Spain) and voluntarily asked to be tes ted for HIV antibodies. The prevalence was estimated for each year based on the serological status of HIV-1 when the patient first visited the centre. The annual incidence rates were calculated based on the seronegative patie nts in which a new determination of HIV-1 was done. In order to control the possible effects on the estimations of age, sex and duration of addiction of the people studied, Poisson and logistic regression models were adjusted . Results Prevalence and incidence rates of HIV-1 infection showed parallel t rends over time. The overall prevalence found was 43.6% (95% confidence int ervals [CI] :42.4-44.7%). Of the 4023 seronegative individuals, 1746 were f ollowed up over the whole of the study period. The incidence rate observed was 6.85 x 100 persons/year (95% CI : 6.04-7.66). The prevalence figures sh ow a decrease, which is most marked from 1990 onwards and then they tend to stabilize over the past few years. The incidence rates increase slightly u p to 1991 (9.8 x 100 persons/year), and then begin to decrease. Conclusion Trends of prevalence of HIV-1 infection approximate trends of su bjacent incidence rate. Despite decrease in HIV-1 infection frequency obser ved over 10 years, both the prevalence and incidence figures continue to be high in absolute terms. It is necessary to intensify and adapt preventive measures to each subgroup at risk of infection and in the case of heterosex ual transmission ensure that the failure observed in the case of IDU is not repeated.