Definition of HIV infection:

HIV infection is a condition caused by the human immunodeficiency virus (HIV). The condition gradually destroys the immune system, which makes it harder for the body to fight infections.

This article provides a general overview. For more detailed information, see:

• AIDS
• Acute HIV infection
• Asymptomatic HIV infection
• Early symptomatic HIV infection

Causes, incidence, and risk factors:

The human immunodeficiency virus (HIV) can be spread by the following:

• Through sexual contact -- including oral, vaginal, and anal sex
• Through blood -- through blood transfusions, accidental needlesticks, or needle sharing
• From mother to child -- a pregnant woman can transmit the virus to her fetus through their shared blood circulation, or a nursing mother can pass it to her baby in her breast milk

People who become infected with HIV may have no symptoms for up to 10 years, but they can still pass the infection to others. After being exposed to the virus, it can take up to 3 months for the HIV ELISA blood test to change from HIV negative to HIV positive.

HIV has spread throughout the U.S. The disease is more common in urban areas, especially in inner cities.

See also: AIDS for a more complete description of how HIV is spread.