Population Estimates and Projections Incorporating AIDS
The estimation and projection procedure for countries seriously affected by HIV/AIDS is somewhat complex. For these countries, the Census Bureau models mortality levels and trends under the hypothetical scenario of no epidemic, then adds estimated AIDS mortality based on measured HIV prevalence, ensuring that the "with-AIDS" mortality levels are consistent with empirical, population-based estimates. The starting point for the procedure is the Census Bureau's HIV/AIDS Surveillance Data Base.
The International Programs Center, Population Division, U.S. Census Bureau, maintains the HIV/AIDS Surveillance Data Base. This database is a compilation of aggregate data from HIV seroprevalence and incidence studies in developing countries. Currently it contains over 100,000 records from various publications, presentations, surveillance reports, and conference proceedings. HIV prevalence points taken from this database are the basis for projecting HIV prevalence and estimating AIDS mortality in countries that have generalized HIV/AIDS epidemics. A generalized epidemic is an epidemic that is widespread in the general population. The U.S. Census Bureau explicitly models AIDS-related mortality for those countries where HIV prevalence is consistently above one percent in pregnant women.
The impact of AIDS mortality is currently modeled explicitly in the estimates and projections for selected countries located in Asia, Latin America and the Caribbean, Sub-Saharan Africa, and Europe.
In 2004, a new application (RUPHIVAIDS) was developed at the Census Bureau which incorporates estimates of HIV prevalence from the Estimation and Projection Package (EPP), an epidemiologically realistic model developed and used by the World Health Organization (WHO) and the Joint United Nations Programme on AIDS (UNAIDS). EPP produces a national "best fit" curve of adult HIV prevalence using sentinel surveillance data pertaining to pregnant women visiting antenatal clinics. In order to model AIDS-related mortality, country-specific adult HIV prevalence estimates from EPP are generated for years from the beginning of the epidemic to 2010 or 2012. The RUPHIVAIDS model projects HIV incidence implied by the EPP estimates of HIV prevalence through 2010 or 2012, and then assumes a decline in HIV incidence of 50 percent by 2050.
In conjunction with these adult HIV prevalence estimates, RUPHIVAIDS applies assumptions from the UNAIDS Reference Group on Estimates, Modelling and Projections about the age and sex distribution of HIV incidence, sex ratios of new infections, the mother-to-child transmission rate, and disease progression in both adults and children. This reference group provides the relevant technical basis for the UNAIDS/WHO global estimates and projections of HIV prevalence. They represent the consensus reached at meetings held with representatives from the United Nations Population Division, U.S. Census Bureau, United Nations Children's Fund (UNICEF), WHO, and UNAIDS among others. Further, the model allows for competing risk of death from AIDS versus other causes.
RUPHIVAIDS works in conjunction with the Census Bureau's cohort component Rural-Urban Projection (RUP) program, which is used to prepare population estimates and projections. RUP is used to produce a "Without-AIDS Scenario" and a "With-AIDS Series."
A hypothetical "Without-AIDS Scenario" is created to model what would have happened if a country had not been affected by the HIV/AIDS epidemic. This scenario is developed by removing preliminary estimates of AIDS mortality from observed mortality data. The resulting non-AIDS mortality is then projected into the future. The "With-AIDS Series" is then generated showing what has happened and what is projected to happen in a country as a result of AIDS mortality and its demographic consequences.
The mortality estimates currently in the IDB include the impact of antiretroviral therapy (ART) for selected countries. The number of adults receiving ART comes from the U.S. Office of the Global AIDS Coordinator, the WHO, and other sources.
Ghys P, N Walker, W McFarland, et al. 2008. Improved data, methods and tools for the 2007 HIV and AIDS estimates and projections. Sexually Transmitted Infections, Vol. 84 (supplement I), i1-i4.
Stover J, P Johnson, B Zaba, et al. 2008. The Spectrum projection package: improvements in estimating mortality, ART needs, PMTCT impact and uncertainty bounds. Sexually Transmitted Infections, Vol. 84 (supplement I), i24-i30.
UNAIDS/WHO. 2007. The UNAIDS/WHO Estimation and Projection Package (EPP 2007). Version 3.0.
WHO. 2008. "Towards Universal Access: Scaling up Priority HIV/AIDS Interventions in the Health Sector, Progress Report 2008."