The disease that came to be called acquired immunodeficiency syndrome
(AIDS) was first identified in the summer of 1981. By that time, nearly
100,000 persons in the United States may have been infected with human
immunodeficiency virus (HIV). By the time the routes of transmission
were clearly identified and HIV was established as the cause of AIDS in
1983, over 300,000 people may have been infected. That number has
continued to increase, with approximately 1,000,000 Americans believed
to be infected in 1991. The epidemic is of great public health concern
because HlV is infectious, causes severe morbidity and death in most if
not all of those infected, and often occurs in relatively young persons.
In addition, the cost of medical care for a person with HIV disease is
high, and the medical care needs of HIV-infected persons place a severe
burden on the medical care systems in many areas. Understanding and
controlling the HIV epidemic is a particularly difficult challenge. The
long and variable period between HIV infection and clinical disease
makes it difficult both to forecast the future magnitude of the
epidemic, which is important for health care planning, and to estimate
the number infected in the last several years, which is important for
monitoring the current status of the epidemic.