What is HIV?

HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). By killing or damaging cells of your body's immune system, HIV progressively destroys your body's ability to fight infections and certain cancers. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections, which are caused by microbes such as viruses or bacteria that usually do not make healthy people sick.

More than 700,000 cases of AIDS have been reported in the United States since 1981, and as many as 900,000 Americans may be infected with HIV. There are as many as 275,000 who may not know they are infected and can pass the virus on.

How is HIV transmitted?

HIV is spread most commonly in these ways:

• By having sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex.
• Through contact with infected blood. Before blood was screened for evidence of HIV infection and before heat-treating techniques were introduced to destroy HIV in blood products, such as factor 8 and albumin, HIV was transmitted through transfusions of contaminated blood or blood components. Today, because of blood screening and heat treatment of blood derivatives, the risk of getting HIV from such transfusions is extremely small.
• By sharing needles or syringes (such as during injection drug use), which can be contaminated with very small quantities of blood from someone infected with the virus. It is rare, however, for a patient to give HIV to a health care worker or vice-versa by accidental sticks with contaminated needles or other medical instruments.
• During pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother takes the drug AZT during pregnancy, she can significantly reduce the chances that her baby will be infected with HIV. If doctors treat mothers with AZT and deliver their babies by cesarean section, the chances of the baby being infected can be reduced to a rate of one percent.
• Having a sexually transmitted disease such as syphilis, genital herpes, chlamydia, gonorrhea, or bacterial vaginosis, which appears to make people more susceptible to and at higher risk for acquiring HIV infection during sex with infected partners.