Transmission of HIV infection refers to the process by which the HIV virus invades a person's body. HIV is transmitted to an uninfected person when HIV-infected body fluids come in contact with the infectable cells (CD4+ cells) of an uninfected person. Body fluids that transmit HIV include blood and blood products, semen, preseminal fluid, vaginal and anal fluids, other body fluids that contain blood, breast milk, brain and spinal cord fluid, fluid around bone joints, and amniotic fluid (Chin, 2000; Mayer & Pizer, 2000; NIAID, 2003). These fluids may contain HIV particles and HIV-infected CD4+ cells, both of which can cause HIV infection.
HIV can reach the infectable cells of a person either through that person's blood or through his or her mucous membranes. Mucous membranes are the linings of certain cavities (such as the nose, mouth, vagina, and anus) that produce a protective layer of mucus. Blood and mucus are infectable because they contain the cells that HIV attacks—that is, CD4+ cells.
Unlike many other illnesses, HIV is not transmitted through routine casual contact, through the air, or through insect bites. This is because HIV does not survive well outside of people's bodies. HIV can be transmitted in the following ways:
HIV can be transmitted during sexual activities that involve direct contact between the HIV-infected person's bodily fluids (such as semen, vaginal secretions, and blood) and the uninfected person's blood or mucous membranes (such as in the vagina, rectum, and mouth). Two people with HIV also can infect each other with different strains of HIV through sexual contact.
Transmission of HIV can occur via skin-piercing instruments, such as needles for injecting drugs, razor blades, tattoo needles, piercing needles, or circumcision instruments, that are used on more than one person. This is because some infected blood may be left on these instruments when they are used on others. In healthcare settings, HIV is sometimes transmitted by accidental stabs from contaminated needles or other sharp objects.
HIV can be transmitted from mother to infant during pregnancy, childbirth, or breastfeeding. This is commonly referred to as mother-to-child transmission, parent-to-child transmission, or vertical transmission. Talk to your healthcare provider about ways to reduce the risk of transmission.
HIV can be transmitted from person to person through transfusions of blood and blood products, such as blood-clotting agents (platelets); organ, tissue, and bone transplants; and artificial insemination. Proper screening of these human products can reduce the risk of transmission through these routes to nearly zero (Donegan, 2003).
Transmission of HIV can occur by splashing mucous membranes (such as eyes) with infected blood or other HIV-infected body fluids (CDC, 2003).
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