What Is It?
AIDS is one of the most serious, deadly diseases in human history.

More than 20 years ago, doctors identified the first cases of AIDS in San Francisco and New York. Now there are an estimated 42 million people living with HIV or AIDS worldwide, and more than 3 million die every year from AIDS-related illnesses.

AIDS is caused by the HIV virus (human immunodeficiency virus). HIV destroys a type of defense cell in the body called a CD4 helper lymphocyte (pronounced: limp-fu-site). Normally these lymphocytes are part of the body's immune system, the defense that fights infectious diseases. But as HIV destroys the lymphocytes, people with the virus begin to get serious infections that they normally wouldn't - that is, they become immune deficient. The name for this condition is acquired immune deficiency syndrome (AIDS).

Half of all new HIV infections in the United States occur in people under 25 years of age, and thousands of U.S. teens become infected with HIV each year. 

HIV can be transmitted from an infected person to another person through blood, semen (also known as "cum," the liquid containing sperm), vaginal fluids, and breast milk.

The virus is spread through high-risk behaviors including:

• unprotected oral, vaginal, or anal sexual intercourse ("unprotected" means not using a condom)
• sharing needles, such as needles used to inject drugs (including needles used for injecting steroids) and those used for tattooing 

People who have another sexually transmitted disease, such as syphilis, genital herpes, chlamydial infection, gonorrhea, or bacterial vaginosis are at greater risk for contracting HIV during sex with infected partners.

If a woman with HIV is pregnant, her newborn baby can catch the virus from her before birth, during the birthing process, or from breastfeeding. If doctors know an expectant mother has HIV, they can usually prevent the spread of the virus from mother to baby. All pregnant teens and women should be tested for HIV so they can begin treatment if necessary.

The HIV virus attaches to these CD4 cells, infects them, and uses them to replicate. In doing so, the virus destroys the ability of the infected cells to do the job of helping transmit messages to other cells of the immune system. The body then loses the ability to fight many infections.

Because their immune systems are compromised, people who have AIDS are unable to fight off many infections, particularly tuberculosis and other kinds of otherwise rare infections of the lung (pneumonia, such as Pneumocystis carinii), the surface covering of the brain (meningitis), or the brain itself (encephalitis). People who have AIDS tend to become progressively more sick, especially if they are not taking antiviral medications properly.

AIDS can affect every body system. The immune defect caused by the absence of CD4 cells also permits some cancers that are stimulated by viral illness to occur - some people with AIDS get forms of lymphoma and rare tumors of blood vessels in the skin called Kaposi's sarcoma. Because AIDS is fatal, it's important that doctors detect HIV infection as early as possible so a person can take medication to delay the onset of AIDS.

How Do People Know They Have HIV?
Once a person's blood lacks the number of CD4 cells required to fight infections, or the person has signs of specific illnesses or diseases identified with active HIV infection, doctors make a diagnosis of AIDS.

Severe symptoms of HIV infection and AIDS may not appear for 10 years, and for years leading up to that, a person may not have symptoms of AIDS. The amount of time it takes for symptoms of AIDS to become evident varies from person to person. Some people may feel and look healthy for years while they are infected with HIV. It is still possible to infect others with HIV, even if the person with the virus has absolutely no symptoms. You cannot tell simply by looking at someone whether he or she is infected.

When a person's immune system is overwhelmed by AIDS, the symptoms can include:

• extreme weakness or fatigue
• rapid weight loss
• frequent fevers that last for several weeks with no explanation
• heavy sweating at night
• swollen lymph glands
• minor infections that cause skin rashes and mouth, genital, and anal sores
• white spots in the mouth or throat
• chronic diarrhea
• a cough that won't go away
• short-term memory loss

Girls may also experience severe vaginal yeast infections that don't respond to usual treatment, as well as pelvic inflammatory disease.

• abstaining from sex (not having oral, vaginal, or anal sex)
• always using latex condoms for all types of sexual intercourse
• avoiding contact with the bodily fluids through which HIV is transmitted
• never sharing needles

How Is It Treated?
If you think that you may have HIV or AIDS or if you have had a partner who may have HIV or AIDS, you need to see your family doctor, adolescent doctor, or gynecologist. He or she will talk with you and perform blood tests. If you're not sure how to contact a doctor, you can contact the National AIDS Hotlines at (800) 342-AIDS (English) or (800) 344-7432 (Spanish) and a specialist there will explain what you should do next.

There is no cure for AIDS, which makes prevention that much more important. Combinations of antiviral drugs and drugs that boost the immune system have allowed many people with HIV to resist infections, stay healthy, and prolong their lives, but these medications are not a cure. Right now there is no vaccine to prevent HIV and AIDS, although researchers are working on developing one.