Acquired immunodeficiency syndrome (AIDS) is an illness that weakens the body's immune system. The immune system of a person with AIDS is not able to fight off certain infections and cancers.

The Immune System

© 2009 Nucleus Medical Media, Inc.

AIDS is caused by the human immunodeficiency virus (HIV), which destroys important immune system cells. HIV is spread through contact with HIV-infected blood or other body fluids, including semen, vaginal fluid, and breast milk. Unprotected sex is the most common mode of transmission. Sharing needles for injecting drugs is another common way the virus is transferred.

More than one million people are living with HIV/AIDS in the United States, and an estimated 56,300 new HIV infections are expected to occur this year. Since the first cases of AIDS were reported in 1981, infection with HIV has grown to pandemic proportions—33 million people are living with the disease worldwide.

What are the risk factors for AIDS?
What are the symptoms of AIDS?
How is AIDS diagnosed?
What are the treatments for AIDS?
Are there screening tests for AIDS?
How can I reduce my risk of AIDS?
What questions should I ask my doctor?
What is it like to live with AIDS?
Where can I get more information about AIDS?