What is AIDS? AIDS stands for Acquired Immunodeficiency Syndrome. Acquired – means that the disease is not hereditary but develops after birth from contact with a disease causing agent (in this case, HIV). Immunodeficiency – means that the disease is characterized by a weakening of the immune system. Syndrome – refers to a group of symptoms that collectively indicate or characterize a disease. In the case of AIDS this can include the development of certain infections and/or cancers, as well as a decrease in the number of certain cells in a person’s immune system. A diagnosis of AIDS is made by a physician using specific clinical or laboratory standards.

HIV Causes AIDS

Before the discovery of human immunodeficiency virus (HIV), the virus that causes AIDS, epidemiologic studies of AIDS patients' sex partners and AIDS cases occurring in blood transfusion recipients before 1985 clearly showed that the underlying cause of AIDS was an infectious agent. Infection with HIV has been the only common factor shared by persons with AIDS throughout the world, including homosexual men, transfusion recipients, persons with hemophilia, sex partners of infected persons, children born to infected women, and health care workers who were infected with HIV while on the job, mainly by being stuck with a needle used on an HIV-infected patient.

Although we know that HIV is the cause of AIDS, much remains to be known about exactly how HIV causes the immune system to break down. Scientists are constantly discovering more information about HIV and AIDS. These discoveries help people learn how to stop transmission of the virus and help people infected with HIV to live longer, healthier lives. One important question to answer is why some people exposed to HIV become infected and others do not. Scientists believe it is most likely because of how infectious the other person is and how they are exposed. For example, more than 90 percent of persons who were exposed through an HIV-infected unit of blood became infected. So we know that blood-to-blood contact is a very efficient way that HIV is spread. On the other hand, many health care workers are splashed with blood or bloody body fluids and this type of exposure has caused very few occurrences of HIV infection. Researchers know how HIV is spread and the ways that people can help protect themselves from being exposed to HIV.

What body fluids transmit HIV?

These body fluids have been proven to spread HIV:

• blood
• semen
• vaginal fluid
• breast milk
• other body fluids containing blood

These are additional body fluids that may transmit the virus that health care workers may come into contact with:

• fluid surrounding the brain and the spinal cord
• fluid surrounding bone joints
• fluid surrounding an unborn baby

How does HIV cause AIDS?

HIV destroys a certain kind of blood cells--CD4+ T cells (helper cells)--which are crucial to the normal function of the human immune system. In fact, loss of these cells in people with HIV is an extremely powerful predictor of the development of AIDS. Studies of thousands of people have revealed that most people infected with HIV carry the virus for years before enough damage is done to the immune system for AIDS to develop. However, recently developed sensitive tests have shown a strong connection between the amount of HIV in the blood and the decline in CD4+ T cell numbers and the development of AIDS. Reducing the amount of virus in the body with anti-HIV drugs can slow this immune destruction.