This is a syndrome that is based on evidence of human immunodeficiency virus (HIV) infection and the development of one or more of a list of opportunistic infections or malignancies for which there is no other explanation (1).
The most common of the defined diseases accounting for up to 80% of the defined AIDS cases are Pneumocystis carinii pneumonia and Kaposi's sarcoma.
The origin of HIV is unknown. The HIV-1 virus has been found in blood samples in Africa that date from the 1960's.
The incubation period from infection with the virus to development of AIDS is highly variable (approximately 1 year to 9 years).