Background: Young adult mortality is very significant in South Africa due to the influence of HIV/AIDS, Tuberculosis (TB), Injuries and Non-Communicable Diseases (NCDs). Previous analyses have mainly focused on assessing the time effect of age and period separately. However, health outcomes often depend on three-time scales, namely age, period, and cohort, which are linearly interlinked. Using Age-Period-Cohort (APC) models, this study estimated the time effects of age, period, and cohort on HIV and TB mortality among young adults in South Africa.
Methods: HIV and TB mortality data and mid population estimates were obtained from Statistics South Africa for the period 1997 to 2015. Mortality data are based on deaths reported to the Department of Home Affairs where the underlying cause of death was HIV or TB based on the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) definition. Observed HIV/AIDS deaths were adjusted for under-reporting, misclassification, and systematic proportion from ill-defined natural deaths. Three-year age, period, and birth cohort intervals for 15-64 years, 1997-2015 and 1934-2000 respectively were used. The Age-Period-Cohort (APC) analysis using the Poisson distribution was used to compute the effects of age, period, and cohort on mortality due to TB and HIV.
Results: A total of 5, 825,502 adult deaths were recorded from the period 1997 to 2015 of which, 910,731 (15.6%) and 252,101 (4.3%) were attributed to TB and HIV, respectively. For both observed mortality rate and estimated relative effects, concave down associations were found between TB, HIV mortality rates and period, age with peaks, at 36-38 and 30-32 years, respectively. A downward trend and inverted V-shape between TB and HIV mortality by birth cohort was found, respectively.
Conclusions: The study found an inverse U-shaped association between TB-related mortality and age, period, and general downward trend with a birth cohort for deaths reported between 1997 and 2015. A concave down relationship between HIV-related mortality and age, period, and inverted V-shaped with birth cohort was found. Our findings have shed more light on HIV and TB mortality rates across different age groups, the effect of changes in the overall TB and HIV management and care on the mortality rates, and whether the mortality rates depend on the year an individual was born.