Global inequality in the burden of tuberculosis: findings from the Global Burden of Disease Study 2021

Introduction

Tuberculosis (TB) is one of the main causes of death in infectious diseases (1-4). In order to curb the development of TB, World Health Organization (WHO) established the End TB Strategy (5), which aims to reduce TB incidence by 90% and mortality by 95% by 2035, compared to 2015. The second milestone of the End TB Strategy requires that by 2025, the incidence rate of TB should be reduced by 50% and the mortality of TB should be reduced by 75% (5). However, the current report shows that these goals may not be achieved. According to the WHO’s “Global TB report 2025”, until 2024, the global incidence rate of TB was reduced by 12%, and the death of TB was reduced by 29% (6). This is related to the burden inequality of TB disease among countries worldwide. The inequality of the burden of TB is particularly evident worldwide, especially in low-income and middle-income countries. A study showed that the difference in socio-economic status directly affects the incidence rate and mortality of TB, especially among the poor and marginalized groups, who often face higher infection risk and worse treatment results (7). For example, in some countries, income inequality is positively related to the incidence rate of TB. In areas with large income gaps, the risk of TB transmission is significantly increased (8). One of The Sustainable Development Goals of the United Nations aimed to reduce inequality among countries, including the burden inequality of TB (6). Only one published letter to the editor has briefly reported the level of inequality in the global TB burden across groups defined by the socio-demographic index (SDI) (9). It reflects the inequality related to SDI. However, factors related to the inequality of TB burden are not limited to SDI and policies aimed at changing the trajectory of TB are often implemented at the national level. Yet the inequality in TB burden among countries remains unclear.

Therefore, in order to observe the inequality of TB burden more comprehensively and systematically, this study used the slope index of inequality (SII) and Gini index based on data from the Global Burden of Disease (GBD) database to describe the global burden inequality of TB at different periods, regions, and ages, to provide reference and basis for future TB control policies. We present this article in accordance with the GATHER reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0894/rc).

Methods

Data source

We extracted data from the GBD 2021 study, which is accessible at GBD Results (https://vizhub.healthdata.org/gbd-results/). The GBD 2021 study compiles nationally representative surveys, censuses, and meta-analysis results, offering a comprehensive epidemiological assessment of 371 diseases and injuries, as well as 88 risk factors across 21 GBD regions and 204 countries/territories from 1990 to 2021 (10,11). Detailed descriptions of these data sources and their validation processes can be found through the Global Health Data Exchange web tool (http://ghdx.healthdata.org/). The disease burden of TB was measured in disability-adjusted life year (DALY). The DALY is a composite measure for population health, calculated by summing years of life lost to premature death and years of healthy life lost due to disability. In GBD 2021, TB is an infectious condition resulting from the bacterium Mycobacterium TB. It encompasses various manifestations, such as pulmonary and extrapulmonary TB, and can be identified through bacteriological confirmation or clinical diagnosis (12). For TB, the ICD-10 codes are A10–A19.9, B90–B90.9, K67.3, K93.0, M49.0, P37.0, and ICD-9 codes are 010–019.9, 137–137.9, 138.0, 138.9, 139.9, 320.4, 730.4–730.6. We extracted the age-standardized rates (ASRs) of DALY and population for 204 countries and territories for every year in the time period 1990 to 2021 from the Global Health Data Exchange. In addition, we also extracted the annual DALY rate and population of each country in 15 age groups (<5, 5–9, 10–14, 15–19, 20–24, 25–29, 30–34, 35–39, 40–44, 45–49, 50–54, 55–59, 60–64, 65–69, and >70 years). The rates expressed as age-standardised are based on the GBD reference population. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Statistical analysis

Although the SII and Gini index were commonly applied to a socioeconomic or ordered categorical variable, the mathematical formulation does not require the ranking variable to be non-health-related. Here, we rank countries directly by their DALY rates to examine the absolute and relative inequality in disease burden across the country distribution. The resulting SII and Gini index therefore reflects a purely health-based gradient, not a socioeconomic gradient. The SII and Gini index in this study should be interpreted as the measure of inequality across ordered country-level DALY rates, not as a measure of health inequality across socioeconomic strata. The SII and Gini index were calculated as standardised metrics to quantify burden inequalities in TB at different periods, regions, and ages globally. The derivation of the SII is based on a linear regression. All countries and territories were ranked by their DALY rate from lowest to highest, with their share of the world’s population as the width of a ‘step’ on the horizontal axis (13). The regression line was estimated by the observation of the midpoint the step and DALY rate of each country or territory. The slope of this line, which is the coefficient of linear regression, is the SII. It represents a measure for the average absolute difference in DALY rates between countries and territories. For SII, 95% confidence intervals (CIs) were derived directly from the linear regression model. The Gini index is based on the Lorenz curve, which plots the cumulative share of global DALY for each country or territory against the cumulative share of world population, ranked by increasing DALY rates. The Gini index is the ratio of the area between the Lorenz curve and the diagonal to the area below the diagonal. It represents the average relative difference in DALY rate between any two of the 204 countries and territories included. The 95% CIs of the Gini index were obtained based on bootstrap. The estimated annual percentage changes (EAPCs) of SII and Gini index were used to evaluate their trends from 1990 to 2021. The EAPC is a measure that estimates the annual percentage rate of change over a specific period using a linear regression model (14). The natural logarithm of SII or Gini index is assumed to vary linearly with time; in the formula Y = α + βX + ε, where Y is the natural logarithm of SII or Gini index, X is the calendar year, and ε is an error term. From this formula, β determines whether there is a positive or negative trend in SII or Gini index. EAPC is calculated as 100×(exp(β)–1). And its 95% CIs were also obtained from the linear regression model. If EAPCs and the lower limit of the 95% CI are both >0, then trend is considered to be increasing. In contrast, if both EAPC estimation and the upper limit of the 95% CI are <0, there is a downward trend. For other values the trend is considered stable. All statistical analyses were performed in R version 3.4.3.

Results

The SII of TB reached an estimated 3,107.34×10⁻⁵ globally in 2021, which decreased by 56.32% than that in 1990 (Figure 1, Table 1). The SII exhibited a decreasing trend (EAPC =−2.73, 95% CI: −2.92 to −2.54) (Figure 1, Table 1). However, the global Gini index of TB shows an increasing trend (EAPC =0.21, 95% CI: 0.18 to 0.23) from 0.57 in 1990 to 0.60 in 2021 (Figure 1, Table 1).

Figure 1 The global trends of inequalities of tuberculosis burden from 1990 to 2021. (A) SII (units: 10⁻⁵). Shaded bands around the trend line represent the 95% confidence intervals for the SII. (B) Gini index. Shaded bands around the trend line represent the 95% confidence intervals for the Gini index. SII, slope index of inequality.

Regarding the geographical regions, the SII increased in three regions: Tropical Latin America, Central Sub-Saharan Africa, Southern Sub-Saharan Africa (Table 1); it decreased in the remaining 18 regions. The highest SII was observed in Central Sub-Saharan Africa in 2021, followed by Southern Sub-Saharan Africa and Eastern Sub-Saharan Africa (Table 1). The trend of Gini index of 21 GBD regions varies with 9 increasing (Central Latin America, North Africa and Middle East, Andean Latin America, Central Europe, Central Sub-Saharan Africa, East Asia, South Asia, Southern Sub-Saharan Africa and Tropical Latin America), 8 decreasing (Southern Latin America, Australasia, Eastern Europe, Oceania, Southeast Asia, high-income Asia Pacific, Western Europe and Caribbean), and 4 remaining stable (high-income North America, Western Sub-Saharan Africa and Eastern Sub-Saharan Africa) (Table 1). The top 3 regions with the highest Gini index in 2021 were North Africa and Middle East, Caribbean and Western Europe (Table 1).

Both SII and Gini index in 2021 generally increased with age, but in the population under 15 for SII and the population under 20 for Gini index, there was a decreasing trend as age increases (Figure 2). For the SII trend from 1990 to 2021, the SII of all age groups showed a decreasing trend (Table 2). However, the Gini index showed different trends in different age groups. The trend was increasing in the age groups of less than 10 years old and over 45 years old. In the age group of 15 to 29 years old, its trend is decreasing, while the trend is stable in the remaining age group (Table 2).

Figure 2 The inequalities of tuberculosis burden in different age groups in 2021. (A) SII (units: 10⁻⁵). Shaded bands around the trend line represent the 95% confidence intervals for the SII. (B) Gini index. Shaded bands around the trend line represent the 95% confidence intervals for the Gini index. SII, slope index of inequality.

Discussion

TB remains a major global public health challenge, despite significant progress in diagnosis, treatment, and prevention over the past few decades (15,16). As one of the top infectious causes of death worldwide, TB disproportionately affects low- and middle-income countries, as well as marginalized populations within high-income regions (17-19). Monitoring health inequalities in TB burden is critical for evaluating the effectiveness of global health strategies and ensuring equitable progress toward elimination. However, there is currently no study that systematically summarizes global TB health inequality among countries. As for the theme of health inequality in TB, only a previous letter reported TB burden inequalities. The letter used SDI as the ranking variable to calculate the SII and concentration index. Their findings reflect socioeconomic-gradient-based inequality (i.e., how TB burden differs across SDI-defined groups). In contrast, our study ranks countries directly by DALY rates (from lowest to highest) and applies SII and Gini index to quantify pure outcome-based distributional inequality across countries, independent of any socioeconomic ordering. In other words, our objective is to measure health inequality per se, as opposed to the association between health and other socioeconomic resources. And our study assessed trends of inequalities in TB burden at country/territory level from 1990 to 2021 to capture both absolute and relative inequalities across 21 GBD regions and different age groups. These are important supplements to the contents not involved in previous studies.

Globally, the SII for TB exhibited a substantial decline of 56.32% from 1990 to 2021, with an EAPC of −2.73. This suggests that absolute inequalities in TB burden have improved over time. However, the Gini index, which measures relative inequality, showed an increasing trend (EAPC =0.21). The SII measures the gradient level of health outcomes, while the Gini index measures the inequality of health distribution. In a study on the inequality of Scotland’s child dental health, there was also a phenomenon of inconsistency between the SII and Gini index (20). According to previous study (12), the TB burden declined in almost all countries in 1990–2021 due to advancements in TB diagnosis, treatment, and public health interventions. Therefore, the inconsistency in the trends of the SII and Gini index should stem from that the high-burden countries experienced a more substantial reduction in TB burden, leading to a narrowing absolute gap in DALYs between high- and low-burden countries, and that the unequal distribution of TB DALYs across populations has intensified. This paradoxical finding, where absolute inequality decreases while relative inequality increases, may reflect uneven progress in TB control, with some regions or countries making faster strides than others. This implies that although the absolute achievements of global TB prevention and control have benefited more vulnerable groups, the systematic uneven distribution of resources still leads to a widening relative gap. A strategy that balances fairness and efficiency needs to be developed by combining two types of indicators.

The study presented reveal significant shifts in TB health inequalities across global regions from 1990 to 2021, measured by SII and Gini index. Globally, most regions show encouraging progress in reducing absolute inequalities (SII), evidenced by largely negative EAPC in SII, suggesting that TB control strategies have gradually benefited countries with high TB burden. Despite global progress in SII, profound regional heterogeneity persists, facing a severe challenge of TB health equity. Sub-Saharan Africa warrants focused attention regarding health inequalities in TB. Central Sub-Saharan Africa experienced significant increase in SII (EAPC: 0.69%), recording the world’s highest 2021 SII (7,084.58×10⁻⁵). Southern Sub-Saharan Africa showed the fastest SII growth (EAPC: 4.27%). Although Eastern and Western Sub-Saharan Africa saw SII reductions, their absolute inequalities remain among the highest globally. While our study did not directly examine the drivers of these inequalities, previous literature suggests a possible explanation, According to previous literature, TB is the main complication of human immunodeficiency virus (HIV) infection. About 12.6% of TB cases and 21.3% of TB deaths are attributed to HIV infection (21). This is more serious in southern Africa, where 60.6% of TB patients are HIV infected, accounting for 12.1% of global TB deaths (21). HIV is a leading cause of morbidity and mortality in sub-Saharan Africa (22,23). Its prevalence varied widely in sub-Saharan Africa and treatment gaps persist (24). Thirty-four percent of people living with HIV in eastern and southern Africa and 60% in western and central Africa remain untreated (24). It is important to note that, tempting as such speculation might be, we emphasize that the interpretations are speculative at this stage. Nevertheless, further research directly analyzing these associations is needed before any firm conclusions can be drawn. Although the SII for TB burden in Tropical Latin America also shows an increasing trend, this SII remains relatively low compared to most other regions. Additionally, it should be noted that the SII estimates for Tropical Latin America and Australasia lack 95% CIs in our results, as each region comprises only two countries, making the calculation unfeasible. The relative health inequalities in TB remain a significant concern across many regions. Among the 21 regions analyzed, nine exhibited an increase in the Gini index, indicating a worsening disparity in the population distribution of TB burden within these regions. Evidence indicates that income inequality and poverty serve as key drivers exacerbating the unequal distribution of TB (25,26). Therefore, future strategies may include targeted interventions in high-burden regions, equity-oriented socioeconomic policies (27), and enhanced monitoring of SII and Gini index to evaluate distributional fairness. Eliminating these health disparities may be critical for achieving equitable global TB control.

The analysis reveals a consistent and significant global decline in TB health inequalities, as measured by SII, across all age groups between 1990 and 2021. This reflects broad improvements in the absolute inequalities of TB burden in all age groups. This reduction likely stems from global TB control initiatives, such as WHO’s End TB Strategy, which expanded vaccination coverage and early interventions (28-30), particularly benefiting younger cohorts. For example, the <5-year group exhibited the steepest SII decline, with an EAPC of −4.39. However, Gini index trends revealed nuanced disparities. While the relative inequalities narrowed among youth and working-age adults (e.g., ages 15–29 years), likely due to employment and education-based interventions, it widened in children aged 0–14 years. This suggests uneven resource allocation or inadequate reach to vulnerable subpopulations. Notably, older adults (≥45 years) experienced concurrent SII declines but rising Gini index values, highlighting gaps in elderly-oriented healthcare and social protection. These findings underscore progress in global TB burden inequality of different age, yet call for targeted measures to address persistent disparities, especially among high-risk groups like children and the elderly. Future study should explore long-term dynamics and interactions with social determinants.

This study has several limitations. First, the data rely on estimates from the GBD study, with some missing data coming from modeling calculations. Second, the analysis focuses on country-level disparities and may not capture subnational variations. Third, this current analysis did not propagate uncertainty from the original GBD estimates (e.g., the uncertainty intervals around each country’s DALY rate). We used the reported point estimates of DALY rates as fixed inputs when calculating both the Gini index and the SII. Finally, the study does not explore the underlying drivers of inequality, such as healthcare systems or socioeconomic factors, which could provide deeper insights for targeted interventions.

Conclusions

This study provides a comprehensive assessment of TB inequalities globally, revealing both progress and persistent challenges. While absolute inequalities have decreased, relative inequalities remain a concern, particularly in certain regions and age groups. The findings underscore the importance of tailoring TB control strategies to consider and address both absolute and relative inequalities. Future research should explore the specific factors driving these inequalities to inform more effective and inclusive TB control strategies.

Acknowledgments

We would like to thank the researchers and participants in the GBD.

Footnote

Reporting Checklist: The authors have completed the GATHER reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0894/rc

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0894/prf

Funding: This study was supported by the National Science Fund for Distinguished Young Scholars (No. 82404762), the Natural Science Basic Research Program of Shaanxi (No. 2020JQ-929), the Research Fund of Health Bureau of Xi’an (No. 2013029), and the Research Fund of Xi’an Children’s Hospital (No. 2021G03).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0894/coif). Z.P. reports support from the Natural Science Basic Research Program of Shaanxi, the Research Fund of Health Bureau of Xi’an, and the Research Fund of Xi’an Children’s Hospital. T.Z. reports support from the National Science Fund for Distinguished Young Scholars. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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