What is HIV / AIDS?
Acquired immune deficiency syndrome (AIDS) is caused by infection with the human immunodeficiency virus (HIV).
HIV specifically targets CD4 T helper cells, which are lymphocytes (white blood cells) that protect the body against infection. Infection with HIV therefore results in depletion of CD4 cells and a fall in the CD4 count.
AIDS is defined as a CD4 count of less than 200/µl in the presence of an AIDS defining condition. AIDS defining conditions (ADC) are either infections that do not develop in people with healthy immune systems (opportunistic infections) or certain specified tumours. The list of AIDS defining conditions has been developed by The US Centres for Disease Control (CDC).