The human immunodeficiency virus (HIV) is a retrovirus that infects cells of the human immune system, destroying or impairing their function. In the early stages of infection, the person has no symptoms. However, as the infection progresses, the immune system becomes weaker, and the person becomes more susceptible to so-called opportunistic infections.

The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS). It can take 10-15 years for an HIV-infected person to develop AIDS; antiretroviral drugs can slow down the process even further.

HIV is transmitted through unprotected sexual intercourse (anal or vaginal), transfusion of contaminated blood, sharing of contaminated needles, and between a mother and her infant during pregnancy, childbirth and breastfeeding.

AIDS stands for acquired immunodeficiency syndrome, a condition first reported in the United States in 1981, that has since become a major worldwide epidemic.

AIDS is caused by HIV (human immunodeficiency virus). By killing or damaging cells of the body's immune system, HIV progressively destroys the body's ability to fight infections and certain cancers. The term AIDS applies to the most advanced stages of HIV infection.

How is HIV spread?

There are several common ways that HIV can be passed from person to person, including:

• Having unprotected sex with someone who is infected
• Using needles or syringes that have been used by people who are infected
• Receiving infected blood products or transplanted organs (Since 1985, the United States actively tests all donated blood for HIV; therefore, the risk of getting HIV in this way in the United States is now extremely low.)
• Transmission from mother to child – An infected mother may pass the virus to her developing fetus during pregnancy, during birth, or through breastfeeding.

If you have a sexually transmitted disease, you may be at higher risk for getting infected with HIV during sex with an HIV-infected partner.

There is no evidence that HIV is spread by contact with saliva or through casual contact, such as shaking hands or hugging, or the sharing of food utensils, towels and bedding, swimming pools, telephones, or toilet seats. HIV is not spread by biting insects such as mosquitoes or bedbugs.