Acquired immune deficiency syndrome (AIDS), first identified in 1981, is an infectious disease characterized by a failure of the body’s immunologic system. As a result, affected individuals become increasingly vulnerable to many normally harmless microorganisms, eventually leading to severe morbidity and high mortality. The infection, spread sexually and through blood, has a high fatality rate, approaching 100 percent. Caused by a human retrovirus known as HIV-1, AIDS can now be found throughout the world – in both Western industrialized countries and also the developing nations of Africa and Latin America.

Although precise epidemiological data remain unknown, public health officials throughout the world have focused attention on this pandemic and its potentially catastrophic impact on health, resources, and social structure. Treatments for the disease have been developed, but there is currently no cure or vaccine.

Etiology and Epidemiology

Beginning in the late 1970s, physicians in New York and California reported the increasing occurrence of a rare type of cancer, Kaposi’s sarcoma, and a variety of infections including pneumocystis pneumonia among previously healthy young homosexual men. Because of the unusual character of these diseases, which are typically associated with a failure of the immune system, epidemiologists began to search for characteristics that might link these cases. AIDS was first formally described in 1981, although it now appears that the virus that causes the disease must have been silently spreading in a number of populations during the previous decade. Early epidemiological studies suggested that homosexual men, recipients of blood transfusions and blood products (especially hemophiliacs), and intravenous drug users were at greatest risk for the disease.