Acceso usuarios
C. Rossi
A modified version of a model for the human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic, proposed at the beginning of the 1990s and recently generalized, is presented as a representation of a problematic drug use epidemic. The model can be used both to estimate relevant epidemic macro-parameters and to carry out scenario analyses. The model is of the “mover-stayer” type and allows for heterogeneous risk behaviour among the susceptible population. Such models treat the “susceptibles” as subdivided into two groups: the “stayers”, that is, the individuals who are considered not to be at risk of infection, and the “movers”, who are at risk. Because of the interactions between infectious individuals (pushers) and the susceptibles, some of the latter may pass into the drug user “compartments” and begin a drug user “career”. The model described here comprises two different stages of hidden drug use. The first (light use) stage, which can be more strictly defined, is the initial (or non-problematic) stage of drug use, following which light drug users can either stop using drugs or pass to hard drug use (or death). Other relevant stages taken into account are the therapy stage, the recidivist use stage (either light or hard use) and the temporary non-use stage (the latter are the visible stages). A simpler version of the model is studied using a Markov hybrid approximation and some “what if” scenario analyses are obtained by simulation. A more complex and realistic model is also outlined for possible further development.
