The future of the HIV pandemic.

The emerging HIV epidemics in countries of Asia and Eastern Europe will contribute significantly to the future of the HIV pandemic. Forecasts of the scale of these epidemics are subject to massive uncertainty, however, mainly because of the sensitivity of predictions to small alterations in parameters that are difficult to estimate. In most of these countries, HIV is currently concentrated among vulnerable populations such as injecting drug users, sex workers and their clients, or men who have sex with men. This distribution suggests an alternative to disease forecasting based on the techniques of risk assessment routinely used by environmental epidemiologists. Exposure mapping, dose-response curves and the concept of acceptable risk are some of the tools that may be useful for HIV risk management. This approach is illustrated by a description of exposure in Indonesia and an assessment of currently accepted risk of death for different causes including HIV in the Russian Federation. Although inappropriate for forecasts of heterosexual HIV transmission, mathematical models are shown to be useful for making qualitative predictions about the relative importance of different behaviours for the spread of HIV over time and for interpreting observed trends in HIV prevalence from sentinel surveillance sites.