About HIV: What is AIDS?

AIDS (Acquired Immunodeficiency Syndrome) is the end-stage of HIV disease, a disease process that begins long before people become physically ill. An individual is considered to have AIDS when their immune system is seriously damaged by HIV. In the United States, an HIV-infected person receives a diagnosis of AIDS following the onset of certain diagnostic opportunistic infections or when his/her CD4+ lymphocyte count is less than 200 cells/ml. (An average CD4 + lymphocyte count for a healthy person is ~1000 cells/ml.)

Symptomatic AIDS is only the tip of the iceberg or top of the pyramid of the total spectrum of HIV disease. Most infected individuals show no signs of illness, but will ultimately progress to the top of the pyramid with many more taking their place in the pool of infected individuals, represented here by the pyramid base.

AIDS was first described in June of 1981 as an unusual disease that was causing individuals - primarily young homosexual men - to lose their ability to fight off otherwise common and non-life-threatening infections. GRID (Gay Related Immune Deficiency), as it was first called, soon was given the name of Acquired Immune Deficiency Syndrome, or AIDS. Those most at risk for acquiring the disease were gay or bisexual men, injectors of illicit drugs, transfusion recipients and hemophiliacs.

The causative agent is a retrovirus discovered at about the same time by Dr. Robert Gallo, an American and Dr.Luc Montagnier, a Frenchman. The virus isolates described by each were determined ultimately to be variants of the same virus, later named the Human Immunodeficiency Virus, or HIV. Not long after the discovery of the virus an antibody test was developed which could detect its presence in blood or body fluids. The test was licensed in 1985.

Through the study of blood samples saved for other reasons, we have glimpses of what the HIV epidemic looked like prior to recognition of the first cases in June 1981. The most important of those studies was the Hepatitis B Cohort of San Francisco. In 1978, the public health community enrolled 6,800 homosexual men in San Francisco to study the spread of hepatitis B and the efficacy of newly developed vaccines for Hepatitis B. The saved serum samples were later examined for antibody to HIV following development of the HIV antibody test. Their findings were remarkable.

Retrospectively, three percent of that cohort was already infected with HIV by 1978. The pool of infection had grown to 12 percent in 1979, and by 1981 when the first AIDS cases had been discovered, 36 percent of that group were already infected. By the early '90s, nearly 80 percent of the study cohort had become infected with HIV. While many still showed no symptoms, the number developing AIDS continued to increase.

Next: How is HIV Diagnosed?