Estimating the Size of the HIV/AIDS Epidemic: Complementary Use of the Empirical Bayesian Back-Calculation and the Mover-Stayer Model for Gathering the Largest Amount of Information

Abstract

The HIV/AIDS epidemic has reached the end of its second decade, and estimations of its size and dynam ics are very important, particularly for developing and planning prevention and therapeutic interventions. Since the HIV infection is characterized by a long asymptomatic period and latency time, observational studies are not suitable to study the epidemic. Dy namic models and the Back-Calculation (BC) methods are two general methodologies which provide estimates and projections of HIV/AIDS incidence and prevalence, while focusing attention on different aspects of the epidemic. For example, the Mover-Stayer (MS) Model, a dynamic compartmental model developed to study the epidemic's spread among a general population, is a useful tool to perform scenario analysis, while the Empirical Bayesian Back-Calculation (EBBC) method allows investigation of the dynamics of the epidemic by risk category. Both methods, with timely updating to reflect changes in the natural history of the HIV/ AIDS epidemic, were recently applied within the EU Concerted Action on Multinational AIDS Scenario Analysis and the Italian Consensus Conference. An overview of some dynamic models and BC methods, and an application of the MS Model and EBBC method to the Italian HIV/AIDS epidemic, are presented here.