HIV is transmitted by direct contact with the bodily fluids of an infected person, including blood, breast milk, vaginal fluids, rectal secretions or semen, according to AIDS.gov. In order for transmission to occur, the fluids must either come into contact with damaged tissue or mucous membranes or be directly injected into the bloodstream.
Having vaginal or anal sex with a person who has HIV is the main mode of transmission for the virus, cautions AIDS.gov. This includes sex between a man and woman or sex between two men. Receptive anal sex is riskier than insertive anal sex, and having multiple sexual partners or other sexually transmitted diseases also heightens the risk of infection.
While sex is the main transmission mode, sharing syringes, needles or other items that are used to prepare injectable drugs is another way that HIV is spread, notes AIDS.gov. Other less common modes of transmission include birth mothers passing the virus to an unborn child during pregnancy, birth or while breastfeeding the child. Accidental pricks with a needle or other object contaminated with the virus is also a possibility for transmission, which is of particular concern for those working in a medical setting. Blood transfusions, bites from HIV-infected people, oral sex, and deep, open mouth kissing when the HIV-infected person has bleeding gums or sores are also possibilities for contracting the virus, although these are rarer transmission modes.