First recognized as a disease in 1981, AIDS now ranks high among the world's most urgent public health problems. AIDS is currently the fifth leading cause of death among adults between the ages of 25 and 44.(1) "Acquired Immune Deficiency Syndrome" is a severe depletion of the immune system that seriously weakens the body's defenses against infection. Death due to AIDS is not caused by the immune deficiency itself, but by infectious organisms that take advantage of the ravaged immune system. A normal, healthy immune system is fully able to fend off most of the diseases that kill people with AIDS.

Although infection by the HIV virus is the accepted cause of AIDS, HIV infection and AIDS are not one and the same. Just because someone tests "HIV positive," indicating their blood contains antibodies to the HIV virus, does not mean they have AIDS. People may not show symptoms of AIDS for many years following initial infection by HIV.

The HIV virus is transmitted from person to person by direct contact with blood or body fluids such as lymph, semen, and vaginal secretions. Intimate sexual activity is the most common route of exposure to the virus. HIV is not spread through kissing or household contact such as sharing a drinking glass with an infected family member. Needle sharing among IV drug users is a major route of transmission. Pregnant women infected with HIV can pass the virus to their unborn babies. Exposure to infected blood or blood products in the health care setting is another possible means of infection, although this accounts for a very small number of AIDS cases.

Once it invades the body, the HIV virus enters the "T4 helper cells," white blood cells that coordinate the various cellular functions of the immune system. The virus then penetrates the T4 cell nucleus and commandeers the cell's DNA, instructing it to make copies of the virus. In effect, HIV turns the T4 cells into virus-making factories. Eventually these cells are destroyed, leaving the immune system crippled. The HIV infected person now has AIDS.

In order to be diagnosed with AIDS, an HIV positive individual must have either: 1) Less than 200 T4 cells per cubic millimeter of blood (In a healthy person the T4 count ranges from 650 to 1200), or 2) One of a list of additional clinical conditions that includes: candidiasis, invasive cervical cancer, CMV virus disease, histoplasmosis, mycobacterium infection, recurrent pneumonia, salmonella bacteria infection, and wasting syndrome due to HIV. People with AIDS may also be inflicted with a rare form of cancer called Kaposi's sarcoma.