HIV prevalence at any given age is the difference between the cumulative numbers of people who have become affected with HIV up to this age and the number who died, expressed as a percentage of the total number alive at this age. The basis of measuring infection is the incidence of HIV among people aged 15-49. HIV/AIDS is one of the world’s most important killers and has its greatest impact on poor countries and poor people. This indicator relates to MDG number six to combat HIV/AIDS, malaria, and other diseases.