Epidemiology of Human Immunodeficiency Virus Type 1 Infection among Homosexual Men Participating in Hepatitis B

and San Francisco, California, were entered into trials of the efficacy of hepatitis B vaccine shortly before the acquired immunodeficiency syndrome (AIDS) epidemic was recognized (1978-1980). The authors analyzed data, including serial blood samples tested for antibody to human immunodeficiency virus type 1 (HIV-1) as well as demo-graphic and behavioral information, to characterize the spread of HIV-1 infection within the cohorts. By the end of 1982, the cumulative incidence of HIV-1 infection was 7.5% in Amsterdam, 26.8 % in New York City, and 42.6 % in San Francisco. Covariate analysis showed that differences in sexual activity (number of male sexual partners) and correlates of sexual activity (age and hepatitis B incidence) accounted for the differences in incidence of HIV-1 infection between the New York City and San Francisco cohorts. These covariates did not explain the lower incidence in the Amsterdam cohort. In conclusion, significant differences were found in the spread of HIV-1 in cohorts of homosexual men in Amsterdam, New York City, and San Francisco. These dissimilarities were probably due to a combination of differences in sexual activity at the time the epidemic began and a later introduction of HIV-1 in Amsterdam. Am J Epidemiol 1993; 137:909-15. acquired immunodeficiency syndrome; hepatitis B virus; HIV; homosexuality; sex be-havior Beginning in the late 1970s, several clini-cal trials were conducted to test the efficacy of recently developed plasma-derived hepa-titis B vaccines. Three of these trials were carried out among large groups of homosex-ual/bisexual men in Amsterdam, the Neth-Received for publication June 5, 1992, and in final for