Defining the Aids HIV Virus

AIDS was first defined by the CDC in 1982, when its cause was not yet known. This early definition focused on the presence of numerous diseases that indicated an immune system deficiency, and the absence of other causes for such immune deficiency (Centers for Disease Control, 1982). In 1985, following the discovery of the virus and the release of the HIV antibody test, this definition was revised to include both laboratory evidence of the presence of HIV infection and additional diseases being found in HIV-infected people. The definition was again revised in 1987, when additional diseases were added to the list.

All of the early AIDS definitions by the CDC were based on symptoms and opportunistic infections found in HIV-infected men. In the late 1980s it became increasingly clear that HIV was clinically quite different in women. Many women were sick and dying from diseases that resulted from HIV infection, yet were not categorized as having AIDS. Consequently, they either were not eligible for, or had a harder time obtaining, some of the benefits made available to people with AIDS, among them Supplemental Security Income (SSI) and Social Security Disability Insurance (SSDI). An AIDS diagnosis means automatic entitlement to SSI and SSDI, but HIV-infected people without an AIDS diagnosis are generally subject to an often lengthy, case-by-case determination of disability. Additionally, in many states qualification for SSI or SSDI is accompanied by eligibility for Medicaid. Thus a protracted determination of disability can mean a long wait and eventual denial of Medicaid benefits.

Basing AIDS definitions on the clinical symptoms of men also led to serious undercounting of AIDS cases in the U.S. In January 1993, primarily to remedy this situation, the CDC expanded its definition of AIDS to include all people' who have a CD4 count under 200 or a CD4 percentage under 14 (Centers for Disease Control, 1992). The CD4 count and percentage are important indicators of how much damage HIV has done to a person's immune system. The CDC also added 3 new illnesses to the 23 AIDS-defining diseases previously listed. These most recent changes were sought by advocates for women, IV drug users, and homeless people, and should make the official definition of AIDS more inclusive.
Modes of HIV Transmission

Thirteen years of clinical observations, field studies, and laboratory experiments have shown that HIV is relatively difficult to transmit. It is transmitted via only three routes: sexual contact; transfer of blood or blood products; and mother to child, through the placenta or breast milk. As the virus cannot pass through unbroken skin, it must gain access through a break in the skin, which allows it to enter the blood stream, or through mucous membranes that line the vagina, rectum, urethra, and mouth. Scientists once believed that a tear in the mucous membrane must be present for HIV infection to occur, but many now accept that infection is possible through intact membranes. Although HIV has been found in semen, vaginal secretions, blood, breast milk, saliva, tears, and urine (Centers for Disease Control, 1985; Friedland & Kline, 1987; Lifson, 1988), transmission has been documented only from the exchange of semen, vaginal secretions, blood, and, in rare cases, breast milk, perhaps because the concentration of HIV in the other body fluids is low.

A single exposure to HIV does not necessarily spread the infection. Although some people report infection after just one exposure, others have been repeatedly exposed to the virus with no subsequent signs of infection. For example, there are many cases of couples having sexual relationships over weeks, months, or even years, in which one partner is infected yet the other shows no signs of HIV. The reasons for this are unclear, but a number of factors may come into play:

    * HIV may be transmitted more effectively at certain times during the course of the infection. Infectiousness may, for example, increase as the immune system deteriorates.
    * Certain strains of HIV may be more easily transmitted than others.
    * Infection with another disease in either partner may make HIV easier to transmit.
    * Ease of transmission may depend upon how the person carrying the virus became infected.

Last updated Jan 4/07