The City Clinic Cohort Study: Hepatitis B, HTLV-III/LAV, and CDC AIDS Project 24.

Anticipating the availability of a safe vaccine, scientists at the Center for Disease Control (CDC) planned for a multicenter study of the prevalence, incidence, and efficacy of an experimental vaccine for hepatitis B in 1977, conducted the study among homosexual male volunteers in five collaborating sexually transmitted infection (STI) clinics in the United States from April 1978 through 1980, and concluded that the candidate vaccine was highly efficacious in preventing infections with the hepatitis B virus. Then something completely unexpected and portentous happened. Some successfully vaccinated as well as other homosexual and bisexual men began to show signs and symptoms of a rare cancer, Kaposi's sarcoma, and opportunistic infections typically associated with severe immunodeficiency. As early as October 1983, members of the Hepatitis B study cohort in San Francisco were invited to return to the city STI clinic for further examinations, testing, and confidential interviews about their sexual and other practices. CDC AIDS Project 24 was designed to help describe the natural history of AIDS, define risk factors, and predict future trends. It produced some of the earliest and most convincing scientific evidence about the seriousness and extent of the AIDS epidemic among homosexual and bisexual men in the United States. How the City Clinic Cohort Study came about and evolved is the focus of this commentary.