National AIDS incidence trends and the extent of zidovudine therapy in selected demographic and transmission groups.

After mid-1987 fewer than the expected number of cases of AIDS were reported in the United States in some demographic and transmission groups but not in others. Gay men (regardless of intravenous drug use), adults with hemophilia, and transfusion recipients exhibited fewer cases than expected based on previously reliable models. These favorable trends could not be explained by assuming earlier cessation of human immunodeficiency virus (HIV) infection. Favorable AIDS incidence trends were not found in heterosexual intravenous drug users or in persons infected through heterosexual contact. White gay men from New York City, Los Angeles, and San Francisco experienced markedly favorable trends, whereas little changes was observed for nonwhite gay men from nonurban areas. AIDS incidence trends were quantitatively consistent with the fraction of AIDS-free persons with severe immunodeficiency who received zidovudine in three cohorts. Gay men in San Francisco used zidovudine more frequently than did adults with hemophilia, while little was used by intravenous drug users in New York City. Data describing the initial national distribution of zidovudine (March 31-September 18, 1987) indicated relatively high use by patients with severe immunodeficiency in those groups, such as urban white gay men, that subsequently experienced fewer cases of AIDS than expected. Available data suggest that zidovudine, perhaps in combination with other therapies, has been one factor contributing to favorable AIDS incidence trends in some groups. Broader application of therapy might further retard the incidence of AIDS, especially in intravenous drug users, persons infected through heterosexual contact, minorities, women, and persons diagnosed outside major metropolitan areas.