ABSTRACT
BACKGROUND: Evaluation of acquired immunodeficiency syndrome (AIDS) prevention strategies requires an on-going follow up of the frequency of human immunodeficiency virus (HIV-1) infection. The aim of this study was to examine the trends in prevalence and incidence of HIV-1 infection among injecting drug users (IDU) during the period 1987-1996. METHODS: Transversal and cohort studies were designed which included a consecutive sample of 7132 IDU who attended three AIDS Prevention and Information Centres in the Region of Valencia (Spain) and voluntarily asked to be tested 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 patients 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 trends over time. The overall prevalence found was 43.6% (95% confidence intervals [CI]: 42.4-44.7%). Of the 4023 seronegative individuals, 1746 were followed 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 show 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 up to 1991 (9.8 x 100 persons/year), and then begin to decrease. CONCLUSION: Trends of prevalence of HIV-1 infection approximate trends of subjacent incidence rate. Despite decrease in HIV-1 infection frequency observed 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 heterosexual transmission ensure that the failure observed in the case of IDU is not repeated.
