Reductions in risk behaviour provide the most consistent explanation for declining HIV-1 prevalence in Uganda

Objective: To monitor the HIV-1 epidemic in Western Uganda and the possible impact of interventions. Design: Results from sentinel surveillance of HIV-1 seroprevalence were com pared with cross-sectional serosurvey data and model simulations. Methods: Age-specific trends in HIV-1 prevalence between 1991 and 1997 amon gst antenatal clinic (ANC) attenders in the town of Fort Portal, where a co mprehensive AIDS control programme has been implemented since 1991, were an alysed. Results were compared with outputs from a mathematical model simula ting the HIV-1 epidemic in Uganda. Two scenarios were modelled. one without and one with behaviour change. Sentinel surveillance data were compared wi th data from a population-based HIV-1 serosurvey at the study site, which w as carried out in early 1995. Results: Data from 3271 ANC attenders identified greater education and bein g single as risk factors for HIV-1 infection. A significant decrease of ris k for women with secondary school education over time was observed, whereas the risk for illiterate women remained high. Among women aged 15-19 years (n = 1045) education and marital status-adjusted HIV-1 prevalence declined steadily from 32.2% in 1991 to 10.3% in 1997. For 20-24-year-old women (n = 1010) HIV-1 prevalence increased until 1993 from 19.9% to 31.7% and decrea sed thereafter (21.7% in 1997). These trends closely follow the prediction of the model simulation assuming behaviour change, and for 1995-1997, confi dence intervals of the HIV-1 prevalence estimate exclude the model output f or an uninfluenced epidemic. No clear trends of HIV-1 prevalence were found in older women (n = 1216) and comparisons with the model were ambiguous. S entinel surveillance data at the time of the population survey closely refl ected results for the female general population sample for the two younger age-groups (15-19 and 20-24 years). In contrast, pregnant women aged 25-29 years showed significantly lower rates than the population sample (20.8% ve rsus 45.1%). Conclusion: HIV-1 prevalence amongst ANC attenders aged 15-24 years can be used to monitor the HIV-1 epidemic in the given setting. Declining trends o f HIV-1 prevalence in women aged 15-19 and 20-24 years most likely correspo nd to a reduced HIV-1 incidence attributable to changes in behaviour. Our d ata also show that sentinel surveillance data need to be age-stratified to give useful information. (C) 1999 Lippincott Williams ei Wilkins.