What Is AIDS?

AIDS (acquired immune deficiency syndrome) is caused by the human immunodeficiency virus (HIV), which kills or impairs cells of the immune system and progressively destroys the body's ability to fight infections and certain cancers. HIV is most commonly spread by sexual contact with an infected partner.

The term AIDS applies to the most advanced stages of an HIV infection. Official criteria for the definition of AIDS are developed by the Centers for Disease Control and Prevention (CDC), which is responsible for tracking the spread of AIDS in the United States. The 2008 CDC definition of AIDS includes all HIV-infected people who have fewer than 200 CD4+ T cells (healthy adults usually have CD4+ T-cell counts of 800 or more). In addition, the definition includes HIV-infected people who have been diagnosed with one or more of 26 clinical conditions (opportunistic infections) that affect people with advanced HIV disease.

According to the CDC, in 2010 more than 1.1 million persons aged 13 years and older were living with an HIV infection in the United States including 207,600 (18%) who were unaware of their infection. An estimated 2.7 million new HIV infections occurred worldwide during 2007, which equates to about five new infections every minute. This indicates that the AIDS epidemic still rages out of control. According to the World Health Organization (WHO), at the end of 2008, there were 33.4 million people living with AIDS globally.

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