The human immunodeficiency virus (HIV) is the leading cause of infectious disease deaths worldwide. As of 2013, approximately 36 million patients died of HIV-related illnesses, and an estimated 35.3 million people were living with HIV infection/acquired immunodeficiency syndrome (AIDS). Although HIV exists everywhere, the vast majority of new infections (95%) occur in individuals living in low- and middle-income countries. As an example, in sub-Saharan Africa, which is the world's most affected region, nearly 1 in every 20 adults are living with HIV.