STUDYING DYNAMICS OF THE HIV EPIDEMIC - POPULATION-BASED DATA COMPARED WITH SENTINEL SURVEILLANCE IN ZAMBIA

Objectives: To establish population-based HIV survey data in selected populations, and to assess the validity of extrapolation from HIV sent inel surveillance amongst antenatal clinic attenders (ANC) to the gene ral population. Methods: in a population survey, adults aged greater t han or equal to 15 years were selected by stratified random cluster sa mpling (n = 4195). The survey was carried out in catchment populations of clinics used for national HIV surveillance. The methodology allows detailed comparisons of HIV infection patterns to be made in two area s (urban and rural). Whereas the sentinel surveillance used serum-base d HIV testing, the population survey used saliva (93.5% consented to p rovide a saliva sample). Results: Surveillance of ANC tended to undere stimate the overall HIV prevalence of the general population, but diff erences were not statistically significant. In the urban area, the adj usted overall HIV prevalence rate of ANC (aged 15-39 years) was 24.4% [95% confidence interval (CI), 20.9-28.0] compared with 26.0% (95% CI, 23.4-28.6) in the general population. The respective rural estimates were 12.5% (95% CI, 9.3-15.6) versus 16.4% (95% CI, 12.1-20.6). Age-sp ecific prevalence rates showed ANC to overestimate infection in teenag ers (aged 15-19 years), whereas in the reverse direction of those aged greater than or equal to 30 years. Teenagers analysed by single year of age revealed both ANC and women in the general population with abou t the same steep increase in prevalence by age, but the former at cons istently higher rates. Extrapolations might be biased substantially du e to the higher pregnancy rates amongst uninfected individuals. Conclu sions: ANC-based data might draw a rather distorted picture of current dynamics of the HIV epidemic. Even though representing an obvious ove rsimplification, extrapolations of overall prevalence rates may correl ate with that of the general population. (C) 1998 Lippincott-Raven Pub lishers.