Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV),[9][10][11] a retrovirus.[12] Following initial infection a person may not notice any symptoms, or may experience a brief period of influenza-like illness.[4] Typically, this is followed by a prolonged period with no symptoms.[5] If the infection progresses, it interferes more with the immune system, increasing the risk of developing common infections such as tuberculosis, as well as other opportunistic infections, and tumors which are otherwise rare in people who have normal immune function.[4] These late symptoms of infection are referred to as acquired immunodeficiency syndrome (AIDS).[5] This stage is often also associated with unintended weight loss.[5]
The World Health Organization first proposed a definition for AIDS in 1986.[26] Since then, the WHO classification has been updated and expanded several times, with the most recent version being published in 2007.[26] The WHO system uses the following categories:
- Primary HIV infection: May be either asymptomatic or associated with acute retroviral syndrome[26]
- Stage I: HIV infection is asymptomatic with a CD4+ T cell count (also known as CD4 count) greater than 500 per microlitre (µl or cubic mm) of blood.[26] May include generalized lymph node enlargement.[26]
- Stage II: Mild symptoms, which may include minor mucocutaneous manifestations and recurrent upper respiratory tract infections. A CD4 count of less than 500/µl[26]
- Stage III: Advanced symptoms, which may include unexplained chronic diarrhea for longer than a month, severe bacterial infections including tuberculosis of the lung, and a CD4 count of less than 350/µl[26]
- Stage IV or AIDS: severe symptoms, which include toxoplasmosis of the brain, candidiasis of the esophagus, trachea, bronchi, or lungs, and Kaposi's sarcoma. A CD4 count of less than 200/µl[26]
Specific adverse events are related to the antiretroviral agent taken.[170] Some relatively common adverse events include: lipodystrophy syndrome, dyslipidemia, and diabetes mellitus, especially with protease inhibitors.[25] Other common symptoms include diarrhea,[170][171] and an increased risk of cardiovascular disease.[172] Newer recommended treatments are associated with fewer adverse effects.[29] Certain medications may be associated with birth defects and therefore may be unsuitable for women hoping to have children.[29]
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