The AIDS Epidemic in Tanzania: Rate of Spread of HIV in Blood Donors and Pregnant Women in Dar es Salaam

Publisher Website
Google Scholar
Abstract
The prevalence of antibodies to HIV in population groups in Dar es Salaam, Tanzania has been monitored from late 1984 through 1991. In the pregnant women and blood donors the doubling time was about 2 years. If, however, the doubling time is calculated from reported cases of AIDS of the whole country, an average doubling time of 10 months is obtained. We point out factors that may bias calculations of the rate of spread of the virus and thus give rise to erroneous projections for the nearest years, especially the so-called transient effect. It is recommended that serosurveys of representative population groups are carried out at regular intervals.Based on test results from blood samples of blood donors, pregnant women, and children (ages 5 to 15 years), data on reported acquired immunodeficiency syndrome (AIDS) cases, and the calculated influence of the "transient effect" (an effect caused by the variability of individual incubation periods), the prevalence of human immunodeficiency virus (HIV) in the total population of Tanzania is approximately 2.8% (650-700,000 cases in 24 million people). For pregnant women, the prevalence of HIV rose evenly from 1.3% in 1984-85 to 14% in 1991, a tenfold increase with an average doubling time of about 24 months. The prevalence in blood donors rose from 2.0% in 1984-85 to 10.0% in 1988, with an average doubling time of about 21-32 months. No children tested positive. The cumulative number of AIDS cases in Tanzania reported to the World Health Organization (WHO) rose from 462 in July 1986 to 27,396 in September 1991, resulting in an average doubling time of 10 months. However, based on information from the Epidemiology Unit of the Tanzanian National AIDS Control Programme, the doubling time for reported AIDS cases, calculated annually, rose from less than half a year to 2 years. In view of this, estimates of rates of spread and future projections should not be based on the number of reported AIDS cases in the first 5 years of the epidemic when the "transient effect" is greatest (a large number of cases will have a short incubation period). Since the doubling times calculated from seroprevalence studies agree with those calculated from AIDS case data in 6-8 year old epidemics, projections should be made based on the former. Epidemiological studies involving sexual behavior would identify target populations for intervention.