Transmission of HIV 

HIV spreads by intimate contact with an infected person.  A person can carry and transmit the HIV virus for many years before any symptoms show themselves.  Forms of intimate contact that can transmit AIDS include the following:
Sexual contact;
Sharing contaminated intravenous needles;
Breastfeeding (mother to baby);
Infected mother to fetus during pregnancy or birth;
Blood transfusions (Rare in countries where blood is screened for HIV antibodies.)

Among adults, HIV is spread most commonly during sexual intercourse with an infected partner.  During intercourse, the virus can enter the body through the mucosal linings of the vagina, vulva, penis, or rectum or, rarely, via the mouth and possibly the upper gastrointestinal tract after oral sex.  The likelihood of transmission is increased by factors that may damage these linings, especially other sexually transmitted infections that cause ulcers or inflammation.

HIV can be transmitted by contact with infected blood, most often by the sharing of needles or syringes contaminated with minute quantities of blood containing the virus.  The risk of acquiring HIV from blood transfusions is extremely small in the United States, as all blood products in that country are screened routinely for evidence of the virus.  There are, however, many countries where not all or very few blood products are srceened.

Almost all HIV-infected children in the United States get the virus from their mothers before or during birth.  In the United States, approximately 25 percent of pregnant HIV-infected women not receiving antiretroviral therapy have passed on the virus to their babies.  In 1994, researchers showed that a specific regimen of the drug AZT (zidovudine) can reduce the risk of transmission of HIV from mother to baby by two-thirds.  The use of combinations of antiretroviral drugs and simpler drug regimens has further reduced the rate of mother-to-child HIV transmission in the United States.

In developing countries, cheap and simple antiviral drug regimens have been proven to significantly reduce mother-to-child transmission at birth in resource-poor settings.  Unfortunately, the virus also may be transmitted from an HIV-infected mother to her infant via breastfeeding.  Thus, development of affordable alternatives to breastfeeding is greatly needed.

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