Infectious, life-threatening condition caused by Human Immunodeficiency Virus (HIV) that inhibits the body's protective immune system. Commonly transmitted through sexual contact, shared intravenous needles/syringes, and unscreened blood transfusions; may also be transmitted to the fetus during pregnancy and through breastfeeding. (Note: From 2004-2006, documents dealing with this concept may have been indexed under "Sexually Transmitted Diseases")