HIV infection/AIDS in the United States during the 1990s

Estimates derived by backcalculation indicate that 628,000 to 988,000 Americans had become infected with human immunodeficiency virus (HIV) as of 1 January 1991. In persons exposed heterosexually, the incidence of HIV infection is still increasing, but in other groups, it is stable or decreasing from peak rates that occurred in the early and mid-1980s. If one assumes a 9-year median incubation period between the time of HIV infection and AIDS in untreated persons, our models yielded a best-fit estimate of 637,000 ever-infected persons as of 1 January 1991. From this population, we projected a plateau of about 55,000 incident cases of AIDS per year between 1991 and 1994, with more cases occurring among drug users than among homosexual men after 1994. Backcalculation models that use a 10-year median incubation period yielded a plausible upper-bound estimate of 988,000 ever-infected persons, and projections of AIDS incidence increased to approximately 70,000 new cases per year by 1994, the majority in homosexual men. Using either model, we project that the number of AIDS cases attributed to heterosexual exposure will increase steadily.