In the legacy version of the population model, mortality from HIV/AIDs was treated separately from other mortality, which was related largely to income growth and increasing life expectancy.  HIV/AIDS was seen to be a special plague-like disease with a likely rise and fall in coming years that should be represented additionally to other mortality.  The HIV/AIDS formulation is still in the legacy code and would be activated in the health model switch ( hlmodelsw ) were turned off.  But normally HIV/AIDS is represented (with fundamentally the same logic) in the health model and those with interest should look at that documentation.