摘要：Objectives. We estimated HIV prevalence rates among young adults in the United States. Methods. We used survey data from the third wave of the National Longitudinal Study of Adolescent Health, a random sample of nearly 19000 young adults initiated in 1994–1995. Consenting respondents were screened for the presence of antibodies to HIV-1 in oral mucosal transudate specimens. We calculated prevalence rates, accounting for survey design, response rates, and test performance. Results. Among the 13184 participants, the HIV prevalence rate was 1.0 per 1000 (95% confidence interval [CI] = 0.4, 1.7). Gender-specific prevalence rates were similar, but rates differed markedly between non-Hispanic Blacks (4.9 per 1000; 95% CI=1.8, 8.7) and members of other racial/ethnic groups (0.22 per 1000; 95% CI=0.00, 0.64). Conclusions. Racial disparities in HIV in the United States are established early in the life span, and our data suggest that 15% to 30% of all cases of HIV occur among individuals younger than 25 years. The estimated incidence of both AIDS and HIV in the United States is believed to be fairly stable after having fallen for several years subsequent to the initial crest of the epidemic. 1 , 2 In contrast, the prevalence of AIDS continues to rise as treatment extends survival rates among individuals with HIV. According to Centers for Disease Control and Prevention (CDC) estimates, more than 174000 people in the United States were living with HIV (without AIDS) as of December 2003, and another 400000 were living with AIDS. 1 On the basis of the age distribution of cases identified through AIDS surveillance systems, estimates suggest that as many as half of all infections occur among individuals younger than 25 years. 3 , 4 CDC data indicate a relatively balanced gender ratio but a large racial disparity among young people with HIV: 41% of 13- to 24-year-olds reported to the CDC HIV surveillance system in 2001 were young women (no other age group exhibited a larger female share of infection); 56% were non-Hispanic Blacks, as compared with 15% of the general population. 5 The current data available on HIV prevalence rates among young people are subject to several limitations. CDC surveillance data on HIV prevalence in the United States are steadily improving but remain incomplete, and they are not well suited to estimating prevalence rates among young adults. The CDC surveillance system identifies only those who choose to be tested for HIV and those who fit screening profiles. Surveys indicate that the testing rate outside of the populations at highest risk remains below 50%. 6 Testing also appears to occur late in the course of infection: 20% of patients are diagnosed with HIV and AIDS in the same calendar month and approximately 40% in the same year. 7 Because HIV infection typically precedes AIDS by about 10 years, this suggests that many individuals are infected well before their HIV diagnosis is recorded and that young people may be underrepresented in surveillance data. Finally, the system does not include all states or regions and thus may not provide representative data. Alternative sources of data on HIV infection among young people include back calculation (imputing dates of infection from dates of AIDS diagnosis) and surveys. Back calculation from incident AIDS cases has become less feasible with the increasingly widespread use of antiretroviral therapy, and the most recent reliable back-calculation estimates are now a decade old. 8 Population-based surveys require very large samples to provide reliable estimates for low-prevalence populations. Data are available from only one such US survey, the National Health and Nutrition Examination Survey (NHANES). NHANES was primarily designed to estimate HIV prevalence rates among adults and thus involved a relatively small sample of young people (approximately 1500 cases). Wave III of the National Longitudinal Study of Adolescent Health (Add Health), a nationally representative, population-based survey, was designed to provide estimates of HIV prevalence rates among 19- to 24-year-olds in the United States. The third wave of Add Health, conducted in 2001–2002, surveyed approximately 14000 young adult men and women. These data, which we examined in this study, provide the first general population estimates of the prevalence of HIV by gender and race among US young adults. In addition, Add Health’s longitudinal design offered a unique opportunity to prospectively assess the nature of nonresponse in a survey context, in that people who dropped out in later waves had information available from earlier waves that could be used in such assessments.
