When anonymous unlinked HIV serosurveys were initiated by CDC in 1988 to document the extent of the epidemic in the United States, information about HIV epidemiology was limited. The surveys were conducted at sentinel sites throughout the country to characterize more fully the leading edge of the epidemic. Participating clinic settings have included STD clinics, DTCs, adolescent and young adult clinics, women’s reproductive health clinics, tuberculosis clinics, sentinel hospitals, clinics serving homeless populations, clinics in correctional facilities, and newborn screening programs. Data from these surveys have provided important information on national and regional HIV prevalence trends within groups defined by age, race/ethnicity, and HIV risk behavior. These data have been instrumental in describing populations with the highest need for preventive services and future care. 

Until the mid-1990s, AIDS case surveillance was the best measure of the magnitude and direction of the HIV epidemic because the time between infection with HIV and the development of AIDS was believed to be relatively consistent. However, since the introduction of new medical treatments that can delay the progression of HIV disease, AIDS case surveillance has not been as representative of HIV epidemiology. Because the characteristics of this delayed progression are variable, AIDS case reporting is much less useful in estimating HIV incidence or monitoring trends in the epidemic. The limitations of AIDS case surveillance have increased the need for accurate estimates of HIV incidence. Recently developed technology that can distinguish recent HIV infections from longstanding infections with the use of a single specimen has led to the ability to conduct cross-sectional serosurveys of HIV incidence. Because incidence is indicative of recent infection, it is an important epidemiologic measure for allocating resources and evaluating prevention programs. 

Uses of Anonymous Survey Data

Anonymous serosurvey data have been used for the following purposes: (1) to provide national and local estimates of the number of persons living with HIV infection; (2) to develop evidence to assist in making decisions on the allocation of resources for prevention activities through HIV prevention community planning; (3) to assist in projecting the number of people who may benefit from HIV-related care and treatment; and (4) to advocate HIV prevention activities such as voluntary testing and counseling services, treatment services, education, safe practices for health care workers, and applied public health research.

An important advantage of anonymous unlinked surveys is that they markedly reduce participation bias in seroprevalence and seroincidence estimates. Numerous studies in different risk populations have shown that HIV prevalence estimates obtained from consented testing underestimate HIV prevalence by differing degrees. This underestimate could occur either because high-risk persons who do not want to know their serostatus or persons who know they are HIV-positive are less likely to participate in voluntary testing. Because testing behavior may differ considerably in racial and ethnic, socioeconomic, and behavioral risk groups, anonymous serosurveys are especially important in providing data that are representative of specific subgroups of the population. HIV Prevalence Trends in Selected Populations in the United States 

Principles of Anonymous Unlinked Surveys

• Methods

  Unlinked surveys use residual sera from blood specimens originally collected for routine clinical purposes. There is no contact between persons whose specimens are included in the surveys and the investigators conducting the surveys. Before the specimens are tested for HIV, demographic and risk information is abstracted from routine medical records and intake forms, and then linked to the residual specimens through a unique study number. After the permanent removal of all personal identifiers, residual specimens, which otherwise would be discarded, are anonymously tested for antibodies to HIV. Neither the HIV test results nor the information obtained from medical records and intake forms can be linked to specific persons (Figure 33). Residual specimens collected for routine medical purposes are tested for HIV type-1 (HIV-1) antibodies by using an HIV-1 or HIV-1/HIV-2 enzyme immunoassay screening kit licensed by the Food and Drug Administration (FDA). Sera that are reactive according to the manufacturer’s instructions are retested in duplicate by using fresh samples from the original unlinked specimen. Repeatedly reactive sera are tested with a Western blot assay licensed by the FDA. Software provided to the sites by CDC automatically generates Western blot interpretations from recorded band patterns according to the recommendations of the Association of Public Health Laboratories and CDC. 

• Ethical considerations

  The Office for Human Research Protections, to which the Secretary of Health and Human Services has delegated the protection of the rights and welfare of human research subjects, has determined that anonymous unlinked surveys are ethical if no interaction takes place with the survey participant solely for the purpose of the surveys and if information that may inadvertently identify a person is not retained. In June 1998, the Office of the Director of CDC and the Division of HIV/AIDS Prevention–Surveillance and Epidemiology, National Center for HIV, STD, and TB Prevention, convened an external panel to conduct an ethical review of HIV anonymous unlinked surveys to address the ethics of these surveys since the introduction of effective therapies. The members of the panel considered the unlinked surveys both ethical and necessary to provide unbiased, accurate data on the current status and direction of the HIV epidemic in specific populations and also to provide reliable information for prevention planning and the allocation of resources. 

  State and local health departments consult with, and submit their protocols for approval to, their local institutional review boards before conducting the surveys. Protocols for the unlinked surveys are submitted annually to the CDC Institutional Review Board for review and approval. 

  The results of anonymous unlinked HIV testing can provide data that can be used to estimate HIV infection in a given population but give no information on individuals. The CDC surveys discussed in this report were conducted in settings that directly provided (or offered referral for) voluntary counseling and testing and provided other referral services. Therefore, each person in the survey had the opportunity to learn his or her HIV status and receive appropriate counseling and referral services.

Figure 33. HIV Seroprevalance Survey

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