HIV infection is spread by sexual contact with an infected person, by sharing needles or syringes (primarily for drug injection) with someone who is infected, or, less commonly (and now very rarely in countries where blood is screened for HIV antibodies), through transfusions of infected blood or blood clotting factors. Babies born to HIV-infected women may become infected before or during birth or through breast-feeding.
The end-stage of the infection, acquired immunodeficiency syndrome (AIDS), results from the destruction of the immune system. AIDS is defined by the presence of one or more “opportunistic” illnesses (other illnesses due to decreased immunity).
Effective combination therapies, introduced in the mid-1990s and widely used in industrialised countries, have had a profound effect on the course of HIV infection, improving the quality of life and delaying the onset of AIDS and death in HIV-infected individuals. However, intolerance to side effects and appearance of resistant strains remain causes for concern.