An estimate of the future size of the tuberculosis problem in sub-Saharan Africa resulting from HIV infection

Abstract

The impact of the human immunodeficiency virus (HIV) on tuberculosis is well documented. Its effect in populations with a high proportion of dually infected individuals is likely to be significant. Sub-Saharan Africa is one such region and to better document the effect of HIV infection on tuberculosis there we developed a mathematical model to predict the likely extra numbers of tuberculosis cases due to it. A mathematical model was developed using a variety of scenarios giving a range of risks for the period 1980-2000. The four scenarios included (1) a low rate of 1% risk of tuberculosis infection in year 0 (1980) with 45% tuberculosis infection prevalence, and an HIV prevalence of 2% in 1989; (2) a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence, and a 2% HIV prevalence in 1989; (3) a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence, and a 10% HIV prevalence in 1989; and (4) a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence and a 20% HIV prevalence in 1989. Under scenarios 1 and 2, a 50-60% increase in smear-positive rates in the subpopulation (15-45 years old) is predicted for the year 2000, under scenario 3, smear-positive rates in the subpopulation in the year 2000 are expected to increase four-fold from the 1980 baseline. Under scenario 4, a 10-fold increase in smear-positive rates in 2000 is expected in the subpopulation. Under this scenario, total disease will have increased 12-fold in the subpopulation.(ABSTRACT TRUNCATED AT 250 WORDS)

PIP: The impact of human immunodeficiency virus (HIV) on tuberculosis is well-documented. Its effect on populations with a high proportion of dually infected individuals is likely to be significant. Sub-Saharan Africa is one such region and in order to better document the effect of HIV infection on tuberculosis in that region, the authors developed a mathematical model to predict the likely extra numbers of tuberculosis due to it. A mathematical model was developed using a variety of scenarios which provided a range of risks for the 1980-2000 period. The 4 scenarios included: a low rate of 1% risk of tuberculosis infection in the year 0 (1980) with 45% tuberculosis infection prevalence and a HIV prevalence of 2% in 1989; a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence and a 2% HIV prevalence in 1989; a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence and a 10% HIV prevalence in 1989; and a 2% risk of tuberculosis infection in year 0 with 60% tuberculosis infection prevalence and a 20% HIV prevalence in 1989. In scenarios 1 and 2, a 50-60% increase in smear-positive rates in the subpopulation (ages 15-45 years old) is predicted for the year 2000; in scenario 3, smear-positive rates in the subpopulation in the year 2000 are expected to increase 4-fold from the 1980 baseline; and in scenario 4, a 10-fold increase in smear-positive rates in the year 200 is expected in the subpopulation. Total disease will have increased 12-fold in the subpopulation in this scenario. These data suggest that there will be a dramatic increase in the number of tuberculosis cases due to HIV infection in sub-Saharan Africa which will likely strain the already fragile health care system in this region. (author's modified)