HIV is the virus that causes Acquired Immune Deficiency Syndrome (AIDS). It damages the body's defenses against infection. The virus first attacks specific lymphocytes, a type of white blood cell in the body's immune (infection-fighting) system that identifies and fights off invading germs. These lymphocytes, called T helper cells (also known as T-cells or CD4 cells), are invaded by the virus, and it multiplies inside the cells. HIV destroys the T-cell and invades other T-cells, damaging the body's ability to fight off invading germs and diseases.

When the number of CD4 cells falls to a very low level, people with HIV become more susceptible to infections and certain rare types of cancer because of a weakened immune response. This weakened immunity (or immune deficiency) is what we call AIDS. When the immune system becomes very weak, HIV can affect all the body systems, including the nervous system, the liver and the eyes.

Although AIDS is always the result of HIV infection, not everyone with HIV has AIDS. In fact, adults who become infected with HIV may appear healthy for many years before developing AIDS.

The first case of AIDS was reported in 1981, but the disease existed unrecognized for many years before being identified. Throughout the world, HIV infection leading to AIDS has been a major cause of illness and death among children, teens and young adults.

• In 2007, UNAIDS estimates that 33.2 million people were living with HIV/AIDS worldwide; new HIV infections are estimated to reach 2.5 million; and an estimated 2.1 million people will die of AIDS-related causes.
• In the United States, experts estimate that 40,000 people get infected with HIV each year. Based upon the latest reports, women, especially women of color, represent a group where the rates are increasing.
• Up to 25% of HIV-infected people are unaware of their infection.
• AIDS has been the sixth leading cause of death in the United States among 15- to 24-year-olds since 1991.
• For these reasons, the Centers for Disease Control and Prevention (CDC) has recommended that all individuals between the ages of 13-64 be tested for HIV annually.

• HIV can be spread through sexual intercourse if one of the partners has the virus. The virus can be found in an infected person's blood, semen and secretions from the cervix (part of a female's uterus) or vagina. A person infected with other sexually transmitted infections (STIs) is at greater risk for becoming infected with HIV, and if an HIV-infected person has another STI, he or she is a better transmitter of HIV. This means that infection with HIV and other STIs increase people's risk for getting HIV infection and passing the infection. All types of sexual contact have been associated with acquiring HIV: man to woman, woman to man, man to man, and woman to woman.
• People who inject drugs also risk becoming infected with HIV. Many people who use needles to inject drugs, including steroids, often share those needles and other injection materials (called works) with others. If a person with HIV shares a needle, he or she can also share the virus, because the virus has been found in the tiny amounts of blood inside the needle and in the cotton and other works used when injecting drugs. Individuals sharing needles and works can also pass hepatitis (liver inflammation caused by hepatitis viruses) and other serious infections to others.
• Can HIV be transmitted through casual contact (shaking hands, hugging, using a toilet, drinking from the same glass, or sneezing and coughing)?
  HIV is not an airborne or food-borne virus and does not live long outside the body, so HIV is not transmitted through day-to-day contact in workplaces, schools or social settings. HIV is not transmitted through shaking hands, hugging, or casual kissing. A person cannot become infected from touching a toilet seat, a drinking fountain, a door knob, dishes, drinking glasses, food or pets.

• It is not possible to reliably diagnose HIV infection or AIDS based on symptoms alone. People living with HIV may feel and look completely well but their immune systems are being damaged. It is important to remember that an infected person can pass HIV, even if they feel healthy.
• New treatments can help an HIV-infected person to maintain a healthy immune system for a much longer time.

• HIV is diagnosed using a combination of blood tests that show the antibodies to HIV in the blood. New rapid "Point-of-Care" tests that use oral fluids can also be used for screening purposes. These are popular for community settings, but like other screening tests, positive tests must be confirmed by a blood test.
• HIV testing is available in many settings (hospitals, neighborhood clinics, health department clinics, and doctors' offices). One of the most common tests is the HIV enzyme-linked immunosorbent assay (ELISA or EIA). This test is very good at detecting antibody to HIV, however, it may detect "look-alike" substances not associated with HIV. To be sure a positive test result is correct, a second test is required to confirm a positive result from an ELISA. For most HIV antibody testing in the United States, an ELISA test is used first, and a second test called the Western Blot is used to confirm a positive ELISA. The Western Blot test looks for antibodies to parts of the virus, and combining this test with the ELISA has been very accurate for identifying the presence or absence of HIV infection.
• A technician, nurse or doctor takes a sample of blood to be used for both parts of the test. Depending on where the test is done, it can take a few days to 2 weeks to get the results. Nearly all testing locations require that you return in person for your test results.
• People infected with HIV will also have their immune system tested. There are two tests that are commonly used: the CD4 count, which measures the T-cells; and the viral load, which measures the amount of virus in the blood. These tests are used to determine how well the immune system is functioning and if treatment is necessary.

• People with AIDS may have more than one opportunistic infection and/or HIV-related cancer at the same time. Certain types of lymphoma, Kaposi's sarcoma or invasive cervical cancer are often diagnosed in HIV-infected persons. Other bacterial and viral infections, such as tuberculosis, shingles, cytomegalovirus (CMV) retinitis, Pneumocystis pneumonia, and histoplasmosis can occur.
• When HIV directly infects organ systems, other complications can occur. In 60% of HIV-infected people, HIV digestive (gastrointestinal) disorders cause weight loss, diarrhea or loss of appetite. Thirty to 50% of patients have neurologic symptoms. These symptoms include headache and peripheral neuropathy (nerve pain or numbness and weakness in the hands and feet). Less often, the heart or the skin may be affected. Many HIV-infected persons suffer from depression or anxiety.

The best way to prevent HIV infection is to avoid behaviors that would involve exposure to infected body fluids, including unprotected sexual intercourse or sharing needles to inject drugs.

• Abstain from sexual intercourse; or,
• Use a latex condom properly, every time you have sexual intercourse, with every partner.
• Limit your sexual partners. The more sex partners you have, the greater your risk of encountering someone who has this or other STIs.
• Stop injecting drugs; or
• Stop sharing needles and works.
• If you are infected, your sexual and needle-sharing partner(s) should be tested.

Antiretroviral (ARV) or highly active antiretroviral therapy (HAART) are terms used to describe medications that inhibit the reproduction of HIV in the body. These medications are usually given as a combination of at least three drugs. If ARV/HAART is effective, the deterioration of the immune system and the onset of AIDS can be delayed for years. Even among people who respond well to HAART, the treatment does not rid the body of HIV. The virus continues to reproduce at a slower pace, so it is important for HIV-infected persons to recognize that they could still spread the infection even if the CD4 count and viral load show their immune system is healthy.