TB morbidity estimates overlook the contribution of post-TB disability : evidence from urban Malawi

Introduction

Despite growing evidence of the long-term impact of tuberculosis (TB) on quality of life, Global Burden of Disease (GBD) estimates of TB-related disability-adjusted life-years (DALYs) do not include post-TB morbidity, and evaluations of TB interventions typically assume treated patients return to pre-TB health. Using primary data, we estimate years of life lost due to disability (YLDs), years of life lost due to premature mortality (YLL), and DALYs associated with post-TB cardio-respiratory morbidity in a low-income country.

Methods

Adults ≥15-years who had successfully completed treatment for drug-sensitive pulmonary tuberculosis in Blantyre, Malawi (February 2016–March 2020) were followed-up for three-years with 6- and 12-

monthly study visits. In this secondary analysis, St George’s Respiratory Questionnaire data were used to match patients to GBD cardio-respiratory health states and corresponding disability weights (DWs) at each visit. YLDs were calculated for the study period and estimated for remaining lifespan using Malawian life-table life expectancies. Years of life lost due to premature mortality (YLL) were estimated using study mortality data and aspirational life expectancies, and post-TB DALYs derived. Data were disaggregated by HIV-status and gender.

Results

At treatment completion 222/403(55·1%) participants met criteria for a cardio-respiratory DW, decreasing to 15·6% after three-years, at which point two-thirds of the disability burden was experienced by women. Over 90% of projected lifetime-YLD were concentrated within the most severely affected 20% of survivors. Mean DWs in the three-years post-treatment were 0·041(HIV-) and 0·025(HIV+), and beyond three-years estimated as 0·025(HIV-) and 0·010(HIV+), compared to GBD DWs of 0·408(HIV+) and 0·333(HIV-) during active disease. Our results imply that the majority of TB-related morbidity occurs post-treatment.

Conclusion

TB-related DALYs are greatly underestimated by overlooking post-TB disability. The total disability-burden of tuberculosis is likely undervalued by both GBD estimates and economic evaluations of

interventions, particularly those aimed at early diagnosis and prevention.