Abstract:
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Background: The World Health Organization (WHO) and the Global Burden of Disease
(GBD) study at the Institute for Health Metrics and Evaluation (IHME) periodically provide
global estimates of tuberculosis (TB) mortality. We compared the 2015 WHO and GBD
TB mortality estimates and explored which factors might drive the differences.
Methods: We extracted the number of estimated TB-attributable deaths, disaggregated
by age, HIV status, sex and country from publicly available WHO and GBD datasets for
the year 2015. We ‘standardized’ differences between sources by adjusting each country’s difference in absolute number of deaths by the average number of deaths estimated
by both sources.
Results: For 195 countries with estimates from both institutions, WHO estimated
1 768 482 deaths attributable to TB, whereas GBD estimated 1 322 916 deaths, a difference of 445 566 deaths or 29% of the average of the two estimates. The countries with
the largest absolute differences in deaths were Nigeria (216 621), Bangladesh (49 863)
and Tanzania (38 272). The standardized difference was not associated with HIV prevalence, prevalence of multidrug resistance or global region, but did show correlation with
the case detection rate as estimated by WHO [r ¼ 0.37, 95% confidence interval (CI):
049; 0.24] or, inversely, with case detection rate based on GBD data (r ¼ 0.44, 95% CI:
0.31; 0.54). Countries with a recent national prevalence survey had higher standardized
differences (higher estimates by WHO) than those without (P ¼ 0.006). After exclusion of
countries with recent prevalence surveys, the overall correlation between both estimates
was r ¼ 0.991. Conclusions: A few countries account for the large global discrepancy in TB mortality
estimates. The differences are due to the methodological approaches used by WHO and
GBD. The use and interpretation of prevalence survey data and case detection rates
seem to play a role in the observed differences. |