Incidence of HIV-1 Infection among Adults in the Kagera Region of Tanzania

Abstract

The results of a population-based follow-up study are presented. The baseline study which started in August 1987, was carried out to determine the prevalence of human immunodeficiency virus HIV-1) infection in the Kagera region of Tanzania. A multistage cluster sampling technique was adopted in the selection of the study population. In the followup survey which started in June 1988. members of the same study population were revisited and studied in order to determine the incidence of HIV-1 infection among those who ware HIV seronegative in the initial survey. HIV serology was conducted by using enzyme-linked immunosorbent assay and all positive sera were confirmed by the Western blot technique. A total population of 1316 adults aged 15–54 years was studied, constituting an average follow-up response rate of 69% in the rural areas and of 59% in the urban area. The overall incidenca of HIV-1 infection among the adult population sample was 13.7 per 1000 person-years at risk with the highest incidence in the urban zone 147.5 per 1000 person-years at risk) and the lowest incidence in one of the three rural zones 14.9 per 1000 person-years at risk). The age-specific annual incidence was highest in the age group 25–34 years for males and in the age group 15–24 for females. From these results it was estimated that the number of newly infected adults in the region each year is about 8200 with a range between 5400 and 11 000 corresponding to the 95% confidence limits on the overall incidence. This observation indicates a serious level of continued transmission of HIV-1 infection in the region. It therefore calls for more intensified control measures against the epidemic at all levels in the country since a similar picture may exist in the other regions.