What is human immunodeficiency virus (HIV)?

Human immunodeficiency virus (HIV) is a virus that attacks the immune system, making it difficult for the body to fight infection and disease. HIV is the same virus that also causes acquired immunodeficiency syndrome (AIDS). However, having HIV does not mean you have AIDS. AIDS is the last and most severe stage of the HIV infection. Some people live with HIV for years or even decades before the condition progresses to AIDS.

Once HIV enters the body, it infects a type of white blood cell called CD4+ cells. These white blood cells are an important part of the immune system that helps you fight infections. As CD4+ white blood cells are attacked and destroyed by HIV, the immune system becomes less able to fight infection and disease.

See an illustration of how HIV reproduces.

What causes HIV?

The infection is caused by the human immunodeficiency virus (HIV).

HIV is spread when blood, semen, or vaginal fluids from an infected person enter another person's body, usually through sexual contact or from sharing needles when injecting illegal drugs. The risk of acquiring HIV from a blood transfusion is now extremely low because all donated blood in the United States is screened for HIV.

What are the symptoms of HIV?

Symptoms of early HIV infection include fever, sore throat, headache, muscle aches, and joint pain. A skin rash may develop, along with abdominal cramps, nausea, vomiting, or diarrhea. Symptoms usually disappear on their own within 2 to 3 weeks. Early symptoms are similar to other viral infections and can be mistaken for influenza or mononucleosis.

After recovering from early symptoms of the initial HIV infection, you may not have symptoms for many years. However, as HIV progresses, symptoms reappear and then remain. These symptoms usually include fatigue, unexplained weight loss, fever, night sweats, and swollen lymph nodes. A health professional may first suspect an HIV infection only when symptoms persist for no other reason.

How is HIV diagnosed?

Your health professional diagnoses HIV with antibody blood tests called the ELISA and the Western blot assay.

A diagnosis of HIV is made after 2 or more positive ELISA tests are confirmed by a positive Western blot assay. Because it may take up to 6 months after the original infection for antibodies to appear, it is important to repeat the tests 6 months after being exposed to the virus.

How is HIV treated?

Treatment for HIV depends on what stage of the infection you are in: early, established, or late (AIDS). If you are in the early stages of HIV, one or two antiretroviral medications (highly active antiretroviral therapy, or HAART) may improve the strength of your immune system and reduce the amount of HIV in your blood (viral load). However, if you have no symptoms and your viral load is low, no treatment may be needed for a time.

If you are in a later or established stage of HIV, using three or more antiretroviral medications (HAART)—sometimes called an anti-HIV "cocktail"—is usually recommended for managing the progression of the virus.

What is acquired immunodeficiency syndrome (AIDS)?

AIDS is a disease caused by the human immunodeficiency virus (HIV). AIDS occurs during the final stage of the HIV infection. AIDS is diagnosed when you have one or both of the following:

• Your CD4+ cell count is below 200 cells per microliter (µL) of blood.
• An opportunistic infection (such as pneumonia) or cancer develops due to an impaired immune system.

More than half of adults with HIV will develop AIDS within 12 or 13 years if their HIV infection is not treated. Young children or adults who rapidly progress through the stages of HIV may develop AIDS within about 3 years. When left untreated, AIDS is often fatal within 18 to 24 months after developing it.

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