AIDS is caused by a virus known as Human Immunodeficiency Virus (HIV), which may undermine the body's immune system, making hosts susceptible to infections and diseases that are not lifethreatening in healthy persons. An HIV-infected person may have no illness symptoms for an extended period. There is currently no cure for AIDS, and persons diagnosed as having end-stage AIDS usually die within 2 years. The test for HIV antibodies indicates whether or not a person was infected at some time in the past. The AIDS virus is transmitted through exposure to contaminated blood, semen, and vaginal secretions, such that it occurs primarily through intimate sexual relations and needle-sharing activities. Transmission from infected mother to newborn infant has also occurred. There is no evidence that AIDS is transmitted through casual social and occupational contact. Persons at high risk of exposure to the AIDS virus are male homosexuals and bisexuals, intravenous drug abusers, and persons who have intimate sexual contact with such individuals. 2 tables and 8 notes.