The impact of HIV and other STDs on human populations. Are predictions possible?

This article presents an overview of the use of mathematical models to study the demographic impact of STDs. Written for the nonmathematician, the article introduces the basic concepts of mathematical epidemiology for infectious diseases, such as the mass-action principle, the threshold density concept, and the basic reproductive rate. Described are the main features that characterize the epidemiology of STDs and those features that differentiate them from other directly transmitted diseases, such as measles, rubella, and others. Also presented are major findings concerning the importance of sexual behavior on the dynamics of STD transmission, and the numerical analysis of the demographic impact on gonococcal and HIV infections using a mathematical model. The epidemiology of these two STDs is explored, as well as how the growth rate of the population can influence the epidemiology of these STDs. Finally, the authors demonstrate how, under some circumstances, early treatment of gonorrhea can reduce the demographic impact of HIV in regions most affected by both diseases.