HIV Transmission: Ultimate Guide To HIV Transmission

HIV Transmission - The ultimate guide to HIV Transmission, including facts and information about HIV Transmission.

HIV Transmission - The Ultimate Guide To HIV Transmission

People contract HIV when certain vulnerable cells are exposed to other people's HIV-infected body fluids. This article describes how HIV is transmitted through sex and drug use; from parent to child; through transfusions, transplants, and artificial insemination; and in health care settings.

Overview Of Transmission Of HIV Infection

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. 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:

Sexual activities: 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 HIV+ people also can infect each other with different strains of HIV through sexual contact.
Injection drug use and other activities in which the skin is pierced: HIV can be transmitted 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 health care settings, HIV is sometimes transmitted by accidental stabs from contaminated needles or other sharp objects.
From parent to child: HIV can be transmitted from mother to infant during pregnancy, childbirth, or breast-feeding. This is commonly referred to as mother-to-child transmission, parent-to-child transmission, or vertical transmission. There is strong evidence that use of antiviral medications during pregnancy markedly reduces the likelihood of vertical transmission of HIV (FHI, n.d.b).
Blood transfusions, transplants, and artificial insemination: 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.
Other contacts with mucous membranes: HIV can be transmitted by splashing mucous membranes (such as eyes) with infected blood or other HIV-infected body fluids.

Conditions for HIV Transmission

The following three conditions must be met for HIV to be transmitted:

HIV must be present. Infection can only happen if at least one of the people involved (e.g., a sexual partner, blood or organ donor, or user of injection drug use equipment) is infected with HIV. Certain behaviors alone, such as anal sex, do not cause HIV infection.
HIV must be present in sufficient quantity. The amount or concentration of HIV in the infected body fluid partly determines whether infection happens. The greater the concentration of HIV in the body fluid, the greater the chance that a person exposed to the body fluid will become HIV-infected. HIV is found in very low concentration—or is absent—in saliva, sweat, tears, and urine. It is found in medium concentration in anal secretions, and in high concentration in blood, semen, vaginal secretions, and breast milk. Thus, only a small amount of infected blood, semen, vaginal fluids, or breast milk is enough to infect someone, whereas much larger amounts of anal secretions are needed for HIV transmission. To date, there are no known cases of HIV transmission through saliva, tears, sweat, or urine. Different people also have different concentrations of HIV, depending, in part, on their stage of HIV disease. In the first, primary stage of infection, people have much higher concentrations of HIV in their blood than they do in the middle, asymptomatic stage of infection. Concentrations of HIV rise during the late stage and full-blown AIDS. It is therefore more likely that an HIV+ person will transmit HIV to an uninfected sexual or injecting partner during the primary stages of infection and when the infection has progressed to advanced HIV disease (AIDS) than during the middle, asymptomatic stage, which can last several years.
HIV must get into the bloodstream. It is not enough just to touch HIV-infected fluid to become infected. Healthy, unbroken skin is an excellent barrier that prevents HIV from getting into the body. HIV can only enter through an open cut or sore, or through contact with the mucous membranes of the anus, rectum, genitals, mouth, or eyes.

Drug-Associated Transmission OF HIV

When a person with HIV infection uses a syringe to inject drugs, the needle is contaminated with a small amount of infected blood. If the needle is shared, the next person to use it may inject the infected blood directly into his or her own bloodstream.

Injection drug use (IDU) accounts for only 5-10% of worldwide HIV infections since the beginning of the HIV/AIDS epidemic. Nevertheless, in some parts of the world, IDU is the major mode of HIV transmission. For example, it is estimated that in China, Malaysia, and Vietnam at least half of HIV infections have resulted from IDU. Rapid spread of HIV through shared use of contaminated IDU equipment also has been observed in parts of Central and Eastern Europe (FHI, n.d.a). Because injection drug users are often linked in tight social networks and commonly share their injecting equipment without properly cleaning it, HIV often spreads very quickly in these populations.

In the United States, IDU transmission accounted for more than 29% of all African American adults and adolescents estimated to be living with HIV/AIDS, and more than 31% of Hispanic adults and adolescents estimated to be living with HIV/AIDS. In contrast, more than 20% of estimated cases among White adults/adolescents were IDU-associated.

Injection drug use contributes to the epidemic's spread far beyond the circle of those who inject because people who have sex with an injection drug user also are at risk for infection through the sexual transmission of HIV. Children born to mothers who contracted HIV through sharing needles or having sex with an IDU may become infected as well.

VERTICAL TRANSMISSION OF HIV

HIV transmission commonly used to describe HIV transmission from parents to their children include mother-to-child transmission, parent-to-child transmission, perinatal transmission, and vertical transmission. Many advocates recommend abandoning the term "mother-to-child" transmission because this term implicitly blames women for infecting their unborn children. Indeed, women and their unborn children are often infected by their own husband/fathers.

HIV can be transmitted from an infected mother to her child during pregnancy, during labor and delivery, or through breastfeeding. Without intervention, such as antiretroviral therapy, the risk of transmission from an HIV+ mother to her child before or during birth is 15-25%. Breastfeeding by an HIV+ mother raises the risk by 5-20%, to a total risk of 20-45%.

Vertical transmission of HIV has been virtually eliminated in the developed world. But, rates remain high in resource-constrained countries, particularly sub-Saharan African countries, where the vast majority of HIV-infected women of childbearing age reside. These high rates are largely a result of these women's lack of access to existing prevention interventions.

HIV Transmission Via Transfusion, Transplantation & Artificial Insemination

HIV Transmission Through Transfusions

HIV transmission through blood transfusions and blood products (such as platelets or plasma) has become rare in developed countries since they began screening all donated blood for HIV antibodies. Outside of developed countries, however, blood safety is not as predictably guaranteed. Currently, 80% of the world's population has access to only 20% of the world's supply of safe blood.

Receiving HIV-infected blood or blood products through a transfusion is the surest way to get HIV. Among those who receive infected blood, 90% become HIV+.

HIV Transmission Through Transplants

A person also can be infected with HIV by receiving an organ, bone, or tissue transplant from an HIV+ person because these body parts have blood in them. HIV has been transmitted through transplantations of kidneys, livers, hearts, pancreases, bones, and skin. The majority of HIV transmission through transplantation happened before 1985, when HIV antibody testing became available.

HIV Transmission Through Artificial Insemination

As of late 2003, 15 women worldwide were known to have been infected with HIV through artificial insemination using sperm from anonymous donors. All but one of these instances of insemination-related infection happened before 1985, when HIV antibody testing became available. Six of those 15 cases occurred in the United States. Because an estimated 75,000 women are artificially inseminated annually in the United States, it seems that HIV transmission from unrelated semen donors was an infrequent event before the availability of HIV testing.

Currently, the U.S. Centers for Disease Control and Prevention (CDC) recommends screening semen donors for HIV antibodies two times: first on the day the semen is collected, and then 6 months later. The semen is frozen in the interim. If the donor is HIV+ 6 months after the donation or if the donor does not return for his 6-month checkup, his semen is not used.

HIV Transmission In Health Care Settings

Patients Transmitting HIV To Health Care Workers

In health care settings, such as hospitals and doctors' offices, workers have been infected with HIV after being stuck with needles containing HIV-infected blood. Less frequently, workers also have contracted HIV after infected blood gets into an open cut or comes in contact with a mucous membrane (such as the eyes or inside of the nose). Research suggests that infection after a needle stick injury is rare, happening about 3 times per 1,000 injuries involving HIV-infected blood.

Health Care Workers Transmitting HIV To Patients

As of 2003, there has been only one documented case of a health care worker giving HIV to patients in the United States. In this case, an HIV-infected dentist gave HIV to six patients. Investigations of 63 HIV+ physicians, surgeons, and dentists and their more than 22,000 patients found no other cases of this type of transmission in the United States.