The Centers for Disease Control and Prevention (CDC), in collaboration with other public health agencies and institutions, conducts standardized unlinked prevalence surveys of human immunodeficiency virus (HIV) infection in designated subgroups of the population as part of a sentinel surveillance system to monitor the HIV epidemic in the United States. This system also includes systematically collected national data from ongoing mass HIV screening programs, which are periodically sent without personal identifiers to CDC. These complementary surveys provide standardized information to local and national public health officials on the extent of HIV infection in geographic areas and population subgroups so that education and prevention programs can be developed and evaluated. The information can also be used to estimate the number of people who may benefit from HIV-related care and treatment.

Of persons who know or suspect that they are infected with HIV or who are at high risk for HIV infection, some may be more likely to participate in studies of HIV prevalence and others may be less likely to do so. Unlinked surveys are conducted to obtain estimates of HIV prevalence that are unbiased by self-selection. Residual blood from specimens originally collected for routine diagnostic purposes are tested for HIV antibodies after all personal identifying information has been permanently removed. Neither HIV test results nor risk information routinely obtained from medical records can be linked to individuals. Thus, no interaction with survey participants can take place solely for the purpose of the unlinked surveys. All clinic sites that conduct unlinked surveys either provide or offer referral for voluntary HIV counseling and testing.

In 1987, CDC began providing technical and financial assistance to state and local health departments to conduct unlinked HIV prevalence surveys in selected clinics serving populations at high risk for HIV infection. Surveys were supported in 17 metropolitan areas during 1997 (Figure 1). Settings included sexually transmitted disease (STD) clinics, drug treatment centers, and adolescent medicine clinics. Clinics were chosen for participation in the surveys by state and local health department personnel on the basis of projected sample size, client demographic and behavioral characteristics, and the ability and willingness of the staff to conduct surveys in accordance with standardized protocols.

In addition to the unlinked surveys, CDC monitors results from HIV-antibody mass screening programs. Since 1987, the U.S. Department of Labor has provided CDC with HIV screening results for entrants to the Job Corps, a federally funded job training program for economically and educationally disadvantaged youth. The U.S. Department of Defense has provided CDC with HIV screening results for civilian applicants to the military service since 1985. Personal identifiers are not sent to CDC.

This report summarizes 1997 data from unlinked prevalence surveys in selected STD clinics, drug treatment centers, and adolescent medicine clinics, as well as screening results for entrants to the Job Corps and applicants for military service in the United States and Puerto Rico. The appendix contains 1994 and 1995 summary data from the Survey of Childbearing Women and the Sentinel Hospital Surveillance System for HIV Infection (both of these surveys were concluded at the end of 1995).