Process models offer opportunities to explore the effectiveness of different programme and policy alternatives by varying input behaviours and model parameters to reflect programmatic/policy effects. The Asian Epidemic Model (AEM) has been designed to reflect the primary groups and transmission modes driving HIV transmission in Asia. The user adjusts AEM fitting parameters until HIV prevalence outputs from the model agree with observed epidemiological trends. The AEM resultant projections are closely tied to the epidemiological and behavioural data in the country. In Thailand and Cambodia they have shown good agreement with observed epidemiological trends in surveillance populations and with changes in HIV transmission modes, AIDS cases, male:female ratios over time, and other external validation checks. By varying the input behaviours and STI trends, one can examine the impact of different prevention efforts on the future course of the epidemic. In conclusion, the AEM is a semi-empirical model, which has worked well in Asian settings. It provides a useful tool for policy and programme analysis in Asian countries.I n contrast to the curve fitting approaches used in the UNAIDS workbooks 1 and the Estimation and Projection Package (EPP), 2 the Asian Epidemic Model (AEM) is a full process model that mathematically replicates the key processes driving HIV transmission in Asia. As a result it has more extensive epidemiological and behavioural input requirements but offers the ability, which these other packages cannot, to examine future scenarios in which prevention and care efforts induce behaviour change. This paper will describe the AEM, explain its use, and discuss actual applications.In 1998, Chin et al proposed that three major factors determined the spread of HIV in Asia: the general pattern of heterosexual risk behaviours, the percentage of men visiting sex workers, and the partner exchange rates of female sex workers.3 With support from the United States Agency for International Development, the AEM was developed to test this hypothesis by implementing a process model focused primarily on the most important transmission routes for HIV in Asia-sex work, marital sex, and injecting drug use-and then testing it against actual epidemiological trends in Asian countries. 4 The goal was to develop a model of sufficient complexity to capture the essential dynamics of Asian epidemics, while keeping it simple enough that behavioural and epidemiological inputs could be obtained from existing data sources.Two key design decisions were made. Firstly, the model would be semi-empirical, not theoretical in nature. It would be patterned after the dominant transmission modes in Asia with appropriate behavioural inputs. However, values for parameters such as HIV transmission probabilities and cofactors would be set on a country specific basis by comparing HIV trends generated by the model directly against observed epidemiological trends, rather than by assuming the parameters to have specific values a priori. Furthermore, impor...
The new methods and data implemented in the 2016 version of Spectrum allow national programs more flexibility in describing their programs and improve the estimates of key indicators and their uncertainty.
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