Prevalence and Incidence of HIV Infection in the United States

Trends in reported AIDS cases do not provide a complete picture of the prevalence of the public health problem that HIV infection poses for a population group, community, or nation, because HIV infection per se precedes the clinical diagnosis of AIDS by many years. In some groups, reported AIDS continues to increase after HIV infection has declined. For example, despite very dramatic declines in HIV incidence associated with blood and plasma transfusions after 1985, when antibody screening of blood donations was instituted in the United States, reported cases of AIDS associated with transfusions and in persons with hemophilia continued to increase through the end of the decade. Conversely, reported AIDS case rates may underestimate greatly the future impact of HIV infection, especially in communities or populations more recently affected by the epidemic.

Most notable are the emerging HIV infection epidemics in Thailand, India, Viet Nam, and other areas of Asia, where few cases of AIDS have reached the clinical horizon. For this reason, AIDS surveillance must be accompanied by carefully conducted HIV serosurveys to accurately monitor the public health problem.

Estimates of the prevalence of HIV infection in the United States by the U.S. Public Health Service (USPHS) in 1997 are between 750,000 and 900,000. In addition, it is estimated that approximately 0.6% of men and 0.1% of women are infected; however, the prevalence is much higher for blacks, where 2% of men and 0.6% of women are estimated to be infected. These estimates were based on both available HIV seroprevalence data and on statistical models using AIDS surveillance data and information on the natural history of infection.

National data on HIV prevalence have been directly measured from HIV testing of first-time blood donors, military recruit applicants, job corps applicants, and surveys of antibody status of newborn infants. The prevalence of HIV infection in both military recruit applicants and blood donors grossly underestimates true HIV prevalence rates because homosexual men, IDUs, and persons with hemophilia are discouraged from applying for military service and actively deferred from donating blood.

The highest HIV prevalence rates detected have been among homosexual or bisexual men, IDUs, and persons with hemophilia who received untreated factor concentrates. Prevalence rates in these groups ranged widely in studies-homosexual/bisexual men, 10 to 70%; IDUs, 1 to 50%; and persons with hemophilia, 15 to 90%. Because most surveys in homosexual men and IDUs were conducted among persons seeking medical care for sexually transmitted diseases (STDs) or treatment for drug abuse, the data may not be completely representative of these populations. HIV prevalence rates in persons with hemophilia A and B were directly related to the amount of clotting factor received prior to 1985. HIV seroprevalence rates among female prostitutes varied widely, from 0 to >50%, with the differences largely attributed to the extent of injecting drug use in the population surveyed and the HIV prevalence among IDUs in the community at that time. HIV prevalence rates among male prostitutes parallel rates in homosexual and bisexual men seen in STD clinics in the same communities.