Age, period and cohort analysis of young adult mortality due to HIV and TB in South Africa: 1997-2015.

Abstract

Young adult mortality is very important in South Africa with the impact of Human Immunodeficiency Virus /Acquired Immune deficiency Syndrome (HIV/AIDS), Tuberculosis (TB), injuries and emerging non-communicable diseases (NCDs). Investigation of temporal trends for adult mortality associated with TB and HIV has often based on age, gender, period and birth cohort separately. The overall aim of this study was to estimate age effect across period and birth cohort; period effect across age and birth cohort; and birth cohort effect across age and period on TB and HIV-related mortality. Mortality data and mid population estimates were obtained from Statistics South Africa for the period 1997 to 2015. Observed HIV/AIDS deaths were adjusted for under-reporting while adjustments for the misclassification of AIDS deaths and the proportion of ill-defined natural causes were made. Three-year age, period and birth cohort intervals for 15-64 years, 1997-2015 and 1934-2000 respectively were used. Age-Period-Cohort (APC) analysis using the Poisson distribution was used to compute effects of age, period and cohort on mortality due to TB and HIV.A total of 5, 825,502 adult deaths from the period 1997 to 2015, of which 910,731 (15.6%) were TB deaths while 252,101 (4.3%) were HIV deaths. A concave down association between TB mortality and period was observed while an upward trend was observed for HIV-related mortality. The estimated TB relative mortality showed a concave down association with age, a peak at 36-38 years was found. There was a concave down relationship between TB relative risk between 1997 and 2015. Findings showed a general downward trend between TB mortality and birth cohort, which 1934 cohort had higher rates of mortality. There was an inverse flatter U-shaped association between age and HIV-related mortality, where 30-32 years was more pronounced. An inverse U-shaped relationship between HIV-related mortality and period from 1997 to 2015 was estimated. An inverted V-shape relationship between birth cohort and HIV-related mortality was estimated. The study has found an inverse U-shaped association between TB-related mortality and age, period and general downward trend with 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. The association between HIV-related mortality and period differs from the officially reported trend with adjustment, which shows an upward progression. Our findings are based on a slight advanced statistical model using Age-Period-Cohort. Using APC analysis, we found a secular trend in TB and HIV-related mortality rates which could contribute certain clues in long-term planning, monitoring and evaluation.