Care and support for people living with HIV/AIDS

Report on the global HIV/AIDS epidemic – June 2000Annex 1.How reliable are estimates of HIVinfection and AIDS deaths?It is important to stress that the estimates given in the table in Annex 2 (see pages124-135) and many of the country- and regional-level figures given elsewhere in thisreport are estimates rather than exact counts of infections or deaths. Every time newestimates of HIV infections or AIDS deaths are released, questions are asked aboutthe source and validity of the data, the methods used to arrive at estimates, andwhether the figures reflect the “reality” of the epidemic.These questions arise for all diseases, especially those common in developing countries,where reporting systems are poor and many births and deaths – and most illnesses– go unrecorded. In fact, in many countries, the information on which HIVestimates are based is better than the information available for most other diseases.The approach to estimating HIV prevalence and AIDS deaths varies according towhether the HIV epidemic has reached the general population, or whether it is stilllargely concentrated in groups with high-risk behaviour.In largely heterosexually driven epidemics where there is evidence that men andwomen in the general population have become infected with HIV in significant numbers,HIV surveillance is based mostly on tests performed among pregnant womenattending antenatal clinics that have been selected as sentinel surveillance sites.Anonymous specimens of blood left over from tests performed as part of routinecare for pregnant women are tested for antibodies to HIV. Many countries with heterosexualepidemics in sub-Saharan Africa and a few countries in Asia and theCaribbean have conducted HIV prevalence studies in selected antenatal clinics moreor less regularly since the end of the 1980s. The more regular the studies, the clearerthe picture of current prevalence. Where data are not available for the current year,all available data points are plotted on a curve, and an estimate for the current yearis made according to what is known about the course of epidemics with predominantlyheterosexual transmission. To account for differences in the spread of HIV,this is generally done separately for urban and for rural areas.Pregnant women seeking antenatal care are chosen for HIV surveillance becausethey provide easy access to left-over blood samples, and because they are fairlyrepresentative of the general population. Even in the least developed countries thecoverage of antenatal care is high. In recent years a series of population-based stud-116