Among adults, HIV transmission usually occurs through sexual contact. Transmission also occurs through contact with infected blood. In children, transmission usually occurs when a child is either nursing or born to a mother infected with HIV, states WebMD.
Damage to the mucosal lining in sex organs, such as the penis, vagina and vulva, can occur from other sexually transmitted diseases and results in inflammation or ulcers. Infected partners most likely transmit the HIV virus through the mucosal lining during sexual intercourse. If the mucosal lining is damaged, there is an increased risk of contracting the virus. In rare instances, sexual contact with the mouth results in transmitting HIV, advises WebMD.
Blood exposure from small amounts of blood present on drug needles and syringes typically occurs with sharing infected needles. Medical advancements have minimized the risk of exposure to the HIV virus from infected blood used in transfusions. The screening process for blood products allows identification and elimination of infected blood before use, according to WebMD.
Most children who contract the HIV virus are infected either before or during birth. About 25 percent of mothers infected with the virus in the United States pass it to their child if they are not on a regimen of antiretroviral medication, explains WebMD.