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Update: Acquired Immunodeficiency Syndrome -- United States, 1991

During 1991, state and territorial health departments reported 45,506 cases (17.9 per 100,000 population) of acquired immunodeficiency syndrome (AIDS) to CDC. As in previous years, most cases (52.7%) were attributable to human immunodeficiency virus (HIV) transmission among homosexual/bisexual men. The proportion of cases among these men during 1991 decreased from that in 1990, while the proportions among women and heterosexual men who were injecting-drug users (IDUs) increased, representing nearly one fourth of reported cases in 1991. This report summarizes the characteristics of persons reported with AIDS in 1991 and compares these data with 1990 (Table 1). *

The number of reported AIDS cases increased by 5%, from 43,352 in 1990 to 45,506 in 1991. Because cases reported in one year may have been diagnosed in earlier years, the number of cases can also be counted based on year of diagnosis with adjustment for reporting delays (1); based on this analysis, the number of diagnosed cases increased an estimated 10% from 1990 to 1991.

Larger proportionate increases in reported cases occurred among women compared with men and among blacks and Hispanics compared with non-Hispanic whites (Table 1). Among regions, the South ** reported the largest number of cases in 1991, as well as the greatest proportionate increase in cases from 1990 (Table 1). However, rates remained highest in the Northeast *** and in the U.S. territories (in which 99% of cases were reported from Puerto Rico).

Among the 10 metropolitan areas **** with the largest number of AIDS cases diagnosed in 1991 (adjusted for reporting delays), the two areas with the greatest percentage increase were the District of Columbia (24.3%) and Miami (22.9%). Other metropolitan areas with large increases were Philadelphia (19.2%), Chicago (11.3%), Newark (10.4%), Atlanta (7.9%), and San Francisco (7.3%).

During 1988-1991, the largest number of cases and the most rapid increase in cases among homosexual/bisexual men occurred in the South (Figure 1). In contrast, in the Northeast, the annual number of diagnosed cases among homosexual/bisexual men remained relatively stable or decreased. The most rapid rate of increase in cases among women and heterosexual men who are IDUs occurred in the South, although the number of AIDS cases among IDUs remained highest in the Northeast (Figure 2). In other regions, cases among IDUs increased more moderately or were stable (Figure 2). Cases among persons exposed to HIV through heterosexual contact increased in all regions (Figure 3) and almost all ethnic groups. The largest number of such cases in 1991 and the most rapid increase in cases during 1988-1991 occurred among persons from the South.

Reported by: Local, state, and territorial health departments. Div of HIV/AIDS, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The findings in this report reflect the evolving nature of the HIV epidemic in the United States, which is a composite of multiple epidemics in different regions and among different groups. During 1991, the proportions of reported AIDS cases increased most among women, blacks and Hispanics, persons exposed to HIV through heterosexual contact, and persons in the South. In contrast, small declines occurred in the number of reported cases among whites, persons in the Northeast, and persons exposed to HIV through homosexual/bisexual contact. Cases attributed to homosexual/bisexual contact still account for more than half of all AIDS cases nationally.

Trends in the occurrence of AIDS reflect earlier trends in HIV infection in various populations and regions. Reductions in HIV transmission by blood and blood products as a result of screening and other procedures implemented in 1985 are now reflected by decreases in AIDS cases among persons with hemophilia and transfusion recipients. Furthermore, reports of HIV infection and other sexually transmitted diseases (STDs) -- a proxy marker for behaviors associated with sexual HIV transmission -- have declined among homosexual/bisexual men in some regions (2-4). These declines in the incidence of HIV infection, beginning in the mid-1980s, contribute to the current slower rate of increase in AIDS cases among homosexual/bisexual men (2). In comparison, STD rates have increased for women, certain racial/ethnic minorities, and persons in younger age groups (5-7). Syphilis rates are highest in the Northeast and South, the regions with the largest number of AIDS cases -- especially cases associated with heterosexual contact (6).

A variety of other factors may also influence national and regional trends in the number of AIDS cases reported, including temporal differences in the introduction of HIV, the extent of use of therapies that delay the onset of AIDS-indicator diseases among HIV-infected persons (8), migration of HIV-infected persons before diagnosis with AIDS, and variations in local reporting practices. Adjustments for estimated reporting delays result in an increase in diagnosed cases of AIDS among homosexual/bisexual men and among persons in the 13-19- and 20-29-year age groups in 1991, when compared with 1990.

Ongoing investigation suggests that differences in reporting practices may be the major cause for the apparent decrease in perinatal cases. Because the incidence of AIDS in women has increased steadily (9), and approximately 6000 births per year are to HIV-infected women (10), it is unlikely that the number of cases of perinatal transmission that occurred in 1991 was less than in 1990.

AIDS cases initially reported as resulting from undetermined means of exposure to HIV are investigated by local or state health officials to determine a possible means of exposure. The increased proportion of such cases during the most recent reporting periods (Table 1) reflects the large number of cases still under investigation.

The results of public health surveillance for AIDS, combined with HIV surveillance and reporting and other measures of the HIV epidemic, illustrate the increasing diversity of persons affected by the HIV epidemic. Persons with AIDS reflect the larger population of HIV-infected persons who are asymptomatic or have other HIV-associated diseases. Trends in AIDS cases highlight the continuing need for HIV prevention and care.


  1. Karon JM, Devine OJ, Morgan WM. Predicting AIDS incidence by extrapolating from recent trends. In: Castielo-Chavez C, ed. Mathematical and statistical approaches to AIDS epidemiology: lecture notes in biomathematics. Vol 83. Berlin: Springer-Verlag, 1989.

  2. Karon JM, Berkelman RL. The geographic ethnic diversity of AIDS incidence trends in homosexual/bisexual men in the United States. J Acquir Immune Defic Syndr 1991;4:1179-89.

  3. CDC. Declining rates of rectal and pharyngeal gonorrhea among males -- New York City. MMWR 1984;33:295-7.

  4. Winkelstein W, Wiley JA, Padian NS, et al. The San Francisco Men's Health Study: continued decline in HIV seroconversion rates among homosexual/bisexual men. Am J Public Health 1988;78:1472-4.

  5. Hahn RA, Magder LS, Aral SO, Johnson RE, Larsen SA. Race and the prevalence of syphilis seroreactivity in the United States population: a national sero-epidemiologic study. Am J Public Health 1989;79:467-70.

  6. Rolfs RT, Nakashima AK. Epidemiology of primary and secondary syphilis in the United States, 1981 through 1989. JAMA 1990;264:1432-7.

  7. Quinn TC, Groseclose SL, Spence M, Provost V, Hook EW. Evolution of the human immunodeficiency virus epidemic among patients attending sexually transmitted disease clinics: a decade of experience. J Infect Dis 1992;165:541-4.

  8. Rosenberg PS, Gail MH, Schrager LK, et al. National AIDS incidence trends and the extent of zidovudine therapy in selected demographic and transmission groups. J Acquir Immune Defic Syndr 1991;4:392-401.

  9. CDC. AIDS in women -- United States. MMWR 1990;39:845-6.

  10. Gwinn M, Pappaioanou M, George JR, et al. Prevalence of HIV infection in childbearing women in the United States: surveillance using newborn blood samples. JAMA 1991;265:1704-8.

    • Single copies of this report will be available free until July 3, 1993, from the CDC National AIDS Clearinghouse, P.O. Box 6003, Rockville, MD 20849-6003; telephone (800) 458-5231. ** South Atlantic, East South Central, and West South Central regions. *** New England and Middle Atlantic regions. **** Metropolitan statistical areas typically include the main city as well as the surrounding urban and suburban areas.

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