The percentage of adults and children currently receiving antiretroviral therapy according to nationally approved treatment protocols (or WHO/Joint UN Programme on HIV and AIDS standards) among the estimated number of people eligible for treatment. The numerator (the number of people receiving antiretroviral therapy) is derived from national programme reporting systems, aggregated from health facilities or other service delivery sites. The denominator (the total number of people eligible for antiretroviral therapy) is generated using a standardized statistical modelling approach. The human immunodeficiency virus (HIV) is a virus that weakens the immune system, ultimately leading to acquired immunodeficiency syndrome (AIDS). The number of HIV-infected adults with a CD4 count less than 350 cells/mm3 are considered to be eligible for treatment. WHO issued new recommendations in June 2013 encouraging all countries to initiate treatment in HIV-infected adults with a CD4 count less than 500 cells/mm3.