In 1987, the U.S. Centers for Disease Control and Prevention (CDC) released the results of a study on the prevalence of HIV infection in the U.S., indicating a shifting emphasis toward defining AIDS as infection with HIV rather than by defining particular indicator disease that characterized late-stage AIDS.

Persons exposed to HIV usually develop detectable levels of antibody against the virus within 6-12 weeks of infection. The presence of antibody indicates current infection, though many infected persons may have minimal or no clinical evidence of disease for years. Counseling and testing persons who are infected or at risk for acquiring HIV infection is an important component of prevention strategy.

Most of the estimated 1.0 to 1.5 million infected persons in the United States are unaware that they are infected with HIV. The primary public health purposes of counseling and testing are to help uninfected individuals initiate and sustain behavioral changes that reduce their risk of becoming infected and to assist infected individuals in avoiding infecting others.