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The authors studied the historical spread of human immunodeficiency virus type 1 (HIV-1) infection in homosexual/bisexual men and projected its future spread in these men using data from an AIDS-free cohort recruited during late 1984 in Baltimore, Maryland; Chicago, Illinois; Los Angeles, California; and Pittsburgh, Pennsylvania. Dates of preentry seroconversion in HIV-1 seroprevalent men were estimated using study entry values of hematologic variables influenced by HIV-1 infection. The authors used survival methods incorporating truncation to determine numbers/dates of seroconversion for men with a pre-1984 AIDS diagnosis who were selectively excluded by design from the 1984 AIDS-free cohort. Overall, the annual seroconversion hazard rose progressively from 0.4% in 1978 to 13.8% in 1983, dropped to 4.6% in 1985, and remained relatively stable at 1.1-2.2% from 1986 to 1990. By January 1990, almost 46% of men who were seronegative in 1978 had seroconverted. The authors estimated historical rates of spread by city, age, education, and ethnicity to examine the effects of these factors in the early and continuing stages of the HIV-1 epidemic. There were striking differences among cities with respect to pre-1985 seroconversion rates but not with respect to post-1985 seroconversion rates. Age, education, and ethnicity were all associated with 1978-1990 seroconversion rates. Future seroconversion among homosexual men was predicted assuming that the "stabilized" 1986-1990 hazards (stratified by age) observed here will be representative of future rates. Truncated Kaplan-Meier methods gave the probability of a seronegative 20-year-old man's remaining seronegative in subsequent years. Such a man has a 20.2% chance of seroconverting before reaching the age of 25 years (a 4.4% yearly hazard). The annual hazard drops to 2.5% between 25 and 30 years, to about 1.5% between 30 and 45 years, and to 1.0% between 45 and 55 years. The overall probability of seroconversion prior to age 55 years is about 50%, with seroconversion still continuing at and after age 55. Given that this cohort consists of volunteers receiving extensive anti-HIV-1 transmission education, the future seroconversion rates of the general homosexual population may be even higher than those observed here.

To determine whether the excess prevalence of human immunodeficiency virus type 1 (HIV-1) infection in US black and Hispanic homosexual men relative to white men can be explained by differences in sociodemographic factors, history of sexually transmitted diseases, or sexual and drug-use behaviors, the authors conducted a cross-sectional analysis of baseline HIV-1 seroprevalence and HIV-1 risk factors among 4,475 non-Hispanic white, 234 Hispanic white, and 194 black homosexual men from four centers in the United States (Baltimore/Washington, DC, Pittsburgh, Chicago, and Los Angeles). HIV-1 seroprevalence was significantly higher in Hispanic men (50%; odds ratio (OR) = 1.83, 95% confidence interval (CI) 1.41-2.39) and black men (47%; OR = 1.62, 95% CI 1.21-2.16) compared with white men (35%). Both Hispanic and black men more frequently reported a history of sexually transmitted diseases. Overall, Hispanics had the highest risk profile and blacks the lowest risk profile with respect to certain high-risk sexual behaviors (e.g., receptive anal intercourse and use of anonymous sexual partners) and recreational drug use. After multivariate adjustment, black race remained a significant independent risk factor for HIV-1 seropositivity (OR = 1.60, 95% CI 1.13-2.26), but Hispanic ethnicity was no longer statistically significant (OR = 1.17, 95% CI 0.82-1.69). Most of the excess HIV-1 prevalent infection among Hispanics was explained by their predominant recruitment from Los Angeles--the study center with the highest HIV-1 seroprevalence--and their greater prevalence of a history of sexually transmitted diseases and certain high-risk sexual practices. By contrast, adjustment for these same risk behaviors failed to explain the observed black-white differences in HIV-1 seroprevalence, and further studies are needed to elucidate the reasons for these unexplained racial differences. HIV-1 educational programs for homosexual men should take into account the behavioral differences that exist between white and minority racial/ethnic groups.

This paper focuses on 76 human immunodeficiency virus type 1 (HIV-1) seroconverters who concurrently participated in the Chicago, Illinois, component of the Multicenter AIDS Cohort Study (MACS) and the Coping and Change Study (CCS) of homosexual/bisexual men between 1984 and 1992. A nested case-control analysis was performed to assess the critical behavioral risk factors associated with incident HIV-1 infection and the consistency of these relations in early (1984-1988) versus later (1989-1992) phases of the study. Univariate results revealed strong early period associations between seroconversion and various measures of receptive anal intercourse (RAI) that became considerably weaker in the study's later period. The weaker associations reflected the overall decline in levels of RAI among the cohort during the 9 years of observation. In contrast, univariate results revealed stronger later period associations between seroconversion and measures of receptive oral intercourse and insertive anal intercourse. Subsequent multivariate testing did not support the hypothesis that receptive oral intercourse and/or insertive anal intercourse have replaced unprotected RAI as important risk behaviours in the homosexual transmission of HIV-1. In conditional logistic regression models combining intercourse measures with indices of drug and condom use, only the latter variables were consistently associated with HIV-1 seroconversion in both early and later study periods. Adjusted odds ratios (ORs) for nonuse of condoms during RAI were consistently significant throughout the study (ORs = 3.7-4.8), while adjusted odds ratios for recreational drug use variables rose dramatically during the latter half of the study (e.g., for use of cocaine, OR = 81.3 (95% confidence interval 8-824) [corrected], and for use of nitrite "poppers," OR = 9.1 (95% confidence interval 1.8-45.5)). The behavioral intervention applications of these findings, as well as their relation to data from other recent cohort studies of HIV-1 seroconversion among homosexual/bisexual men, are discussed.

To estimate the time interval between human immunodeficiency virus type 1 (HIV-1) seroconversion and acquired immunodeficiency syndrome (AIDS) diagnosis in homosexual men, prospective incident cohorts are difficult to obtain and, if assembled, provide few events owing to the long incubation time. Although seroprevalent cohorts are numerous in size and events, the information is limited due to the unknown times since seroconversion. To combine the information provided by 1,628 seroprevalent men (304 AIDS cases) and 233 seroconverters (12 AIDS cases) being followed in a multicenter study since 1984, the postseroconversion changes in hematologic variables occurring in the incident cohort were used to develop a model that allowed for the imputation of the unknown times since seroconversion for the seroprevalent cohort. Nonparametric life table methods incorporating truncation and censoring were applied for the estimation of the probability distribution of the AIDS-free time after seroconversion. The precision of the estimates was evaluated using bootstrap methods. The analysis suggested that AIDS is unlikely (less than 0.5%) in the first year; 78% of seropositive homosexual men remain AIDS-free 60 months after seroconversion; and the AIDS incidence increases for months 12-36 and levels off at 38 per 1,000 person-semesters for months 42-60. The nonparametric estimate of the incidence rate suggests a median AIDS-free time of 11 years, which is longer than previous estimates based on parametric models.

Interviews regarding medical history, life-style, specific drug taking and sexual activities, and physical examinations were administered to 4,955 homosexual men who volunteered for the Multicenter AIDS Cohort Study in Baltimore, Chicago, Los Angeles, and Pittsburgh. Overall, the prevalence of antibodies to human immunodeficiency virus (HIV) in these men was 38.0%. The factor most strongly associated with prevalent HIV infection according to a multiple logistic regression model was rectal trauma, a composite variable which included receptive anal fisting, enemas before sex, reporting of blood around the rectum, and the observation of scarring, fissures or fistulas on rectal examination. Receptive anal intercourse also was strongly associated with HIV infection in the model. The multivariate relative odds for HIV antibody positivity was 7.72 for the highest level of rectal trauma and 3.04 for receptive anal intercourse. Symptoms reported to occur in some persons who subsequently develop acquired immunodeficiency syndrome (AIDS) were frequent among HIV seropositive men (12.9%) but were reported in 8.4% of seronegative men as well. Generalized lymphadenopathy was observed significantly more often in seropositive men (48.8%) compared with seronegative men (11.4%). The prevalence of HIV antibodies was inversely related to the number of T-helper cells and directly related (to a lesser extent) to the number of T-suppressor cells. The results suggest that disruption of the rectal mucosa provides access by HIV to the blood stream and to specific immunologic cells. Since symptoms and generalized lymphadenopathy were often reported among seronegative men, they probably also occur among some seropositive men not currently progressing to AIDS.