Rethinking tuberculosis morbidity quantification: a systematic review and critical appraisal of TB disability weights in cost-effectiveness analyses

Background: The disability-adjusted life year (DALY), a key metric for health resource allocation, encompasses morbidity through disability weights. Widely used in tuberculosis cost-effectiveness analysis (CEAs), DALYs play a significant role in informing intervention adopt/reject decisions. This study reviews the values and consistency of disability weights applied in TB-related CEAs.

Methods: We conducted a systematic review using the Tufts CEA database, updated to July 2023 with searches in Embase, Scopus, and PubMed. Eligible studies needed to have included a cost-per-DALY ratio, and additionally either evaluated a tuberculosis intervention or included tuberculosis-related weights. We considered all tuberculosis health states: with/without HIV-coinfection, TB-treatments, and treatment side-effects. Data were screened and extracted independently by combinations of two authors.

Findings: 105 studies spanning 2002-2023 across 50 countries (mainly low- and middle-income) were extracted. Disability weights were sourced primarily from the Global Burden of Disease (GBD) (100/165;61%) with 17 non-GBD studies additionally referenced, along with primary derivation. Inconsistencies in the utilisation of weights were evident: of the 100 usages of GBD-sourced weights, only in 47 instances (47%) had the weight value been explicitly specified with an appropriate up-to-date reference cited (constituting 28% of all weight usages, 47/165). Sensitivity analyses on weight values had been conducted in 30% of studies (31/105). Twelve studies did not clearly specify weights or their sources; nine further calculated DALYs without morbidity. The review suggests methodological gaps in current approaches for representing important aspects of TB, including TB-HIV coinfection, treatment, drug-resistance, extrapulmonary-TB, and psychological impacts. We propose a set of best-practice recommendations.

Interpretation: There is a need for increased rigour in the application, sensitivity testing and reporting of TB disability weights.

Furthermore, there appears a desire among researchers to reflect elements of the tuberculosis experience beyond those allowed for by GBD disability weights.