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Current Trends Update: Acquired Immunodeficiency Syndrome in the San Francisco Cohort Study, 1978-1985

Between 1978 and 1980, a cohort of approximately 6,875 homosexual and bisexual men who had sought evaluation for sexually transmitted diseases at the San Francisco (California) City Clinic was enrolled in a series of studies of the prevalence, incidence, and prevention of hepatitis B virus infections (1,2). In 1981, six of the first 10 men reported with acquired immunodeficiency syndrome (AIDS) in San Francisco were discovered to be members of the City Clinic cohort. Subsequently, the Department of Public Health and CDC began a study of cohort members for AIDS and for infections with human T-lymphotropic virus type III/ lymphadenopathy-associated virus (HTLV-III/LAV), the cause of AIDS.

In a representative sample of cohort members, prevalence of antibody to HTLV-III/LAV, measured by an enzyme immunosorbent assay (EIA), increased from 4.5% in 1978 to 67.3% in 1984 (3). From January through August 1985, HTLV-III/LAV antibody prevalence further increased to 73.1% (Figure 1). The number of AIDS cases reported among cohort members increased from 166 in 1984 to 262 in August 1985 (Figure 2).

Thirty-one members of the sample who consented to have their earliest specimens tested had antibody to HTLV-III/LAV at the time they enrolled in studies between 1978-1980. By December 1984, two (6.4%) (95% confidence bounds 0.8%-21.4%) had developed AIDS, and eight (25.8%) had AIDS-related conditions, as defined elsewhere (3). Symptomatic infections with HTLV-III/LAV thus had occurred in 10 (32.2%) (95% confidence bounds 16.7%-51.4%) of the 31 men after a follow-up period averaging 61 months. No further cases of AIDS have been reported in the 29 men through the first 8 months of 1985.

Sixty members of the cohort who were seronegative in 1984 were tested again in 1985, an average of 14 months (range 9-18) after their last specimens were collected; nine (15.0%) were found to have developed antibodies to HTLV-III/LAV. Five of the nine had reduced their numbers of sexual partners since their last visit; two had not changed; and two had increased their numbers slightly. Each man who seroconverted had engaged in sexual activities that resulted in the exchange of semen and other body fluids. Two seroconverters who reported sexual exposures with only one steady partner since their last negative test had engaged in receptive anal intercourse with ejaculation by their respective partners.

Men who remained seronegative were not shown to differ significantly in sexual practices from those who seroconverted, but the number of seroconverters available for comparison is small. Reported by D Echenberg, MD, G Rutherford, MD, P O'Malley, T Bodecker, San Francisco Dept of Public Health; AIDS Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The cumulative incidence of AIDS in City Clinic cohort members is now 3,825 per 100,000, the highest of any reported population (4,5). Almost three-quarters of cohort members now have serologic evidence of HTLV-III/LAV infections. The long-term prognoses for these men is unknown. The fact that two-thirds of men infected for over 5 years have not developed AIDS or AIDS-related illness is an encouraging indication that infection with this virus is not necessarily followed by rapid development of symptoms and death.

Studies from New York City, San Francisco, and elsewhere suggest that many gay men have changed their sexual lifestyles (5). Between 1980 and 1983, rates of rectal and pharyngeal gonorrhea in men in Manhattan decreased 59% (6). Surveys of self-reported behavior of gay men in San Francisco have shown decreases in both the average number of sexual partners and sexual practices known to transmit HTLV-III/LAV infection (7,8). However, as the prevalence of HTLV-III/LAV infection in a population increases, substantial changes in both the numbers of sexual partners and types of sexual practices will be necessary to reduce the risk that susceptible gay men may become infected.


  1. Schreeder MT, Thompson SE, Hadler SC, et al. Hepatitis B in homosexual men: prevalence of infection and factors related to transmission. J Infect Dis 1982;146:7-15.

  2. Francis DP, Hadler SC, Thompson SE, et al. The prevention of hepatitis B with vaccine. Report of the Centers for Disease Control multi-center efficacy trial among homosexual men. Ann Intern Med 1982;97:362-6.

  3. Jaffe HW, Darrow WW, Echenberg DF, et al. The acquired immunodeficiency syndrome in a cohort of homosexual men: a six-year follow-up study. Ann Intern Med 1985;103:210-4.

  4. Hardy AM, Allen JR, Morgan WM, Curran JW. The incidence rate of acquired immunodeficiency syndrome in selected populations. JAMA 1985;253:215-20.

  5. Curran JW, Morgan WM, Hardy AM, Jaffe HW, Darrow WW, Dowdle WR. The epidemiology of AIDS: current status and future prospects. Science 1985;229:1352-7.

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

  7. Bye L. Designing an effective AIDS prevention campaign strategy for San Francisco: results from the first probability sample of an urban gay male community. San Francisco, California: Research and Decisions Corporation, 1984.

  8. McKusick ML, Horstman W, Coates TJ. AIDS and sexual behavior reported by gay men in San Francisco. Am J Public Health 1985;75:493-6.

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