Attributable is preventable: Corrected and revised estimates of population attributable fraction of TB related to undernutrition in 30 high TB burden countries

Abstract

Introduction: The Global TB Report 2020 estimated the population attributable fractions (PAF) for the major risk factors of TB. Undernourishment emerged as the leading risk factor accounting for 19% of the cases. The WHO however used the terms undernourishment and undernutrition interchangeably in its computation of PAF. Undernourishment is an indirect model derived estimate of decreased per capita energy availability, while undernutrition is defined by direct anthropometric measurements of nutritional status. An estimate of PAF for a risk factor should use the prevalence and the risk ratio of the same risk factor, which is not the case with the current methodology.

Methods: We re- estimated the PAF of undernutrition (instead of undernourishment) in 30 high TB burden countries as defined by WHO for the period 2016-2020, using the prevalence of undernutrition (age standardized estimate of BMI < 18.5 kg/m² in adults for both sexes), and the relative risk (RR) of 3.2. Further, we revised PAF estimates of undernutrition with an RR of 4.49 (95% CI: 2.28, 8.86), in light of recent evidence.

Findings: In 30 high TB burden countries, 24.1% (95% CI: 17.6,30.0) of incident TB is attributable to undernutrition. The PAF of undernutrition was highest in Asian countries, unlike the PAF of undernourishment that was highest in Africa. The corrected estimate led up to 65% increase in number of cases attributable to undernutrition in Asian countries. If a revised relative risk was used, 33.0% (95% CI: 10.1, 60.1) of incident TB cases in the selected countries could be attributable to undernutrition. More than one-third to nearly half of incident TB cases in India could be attributable to undernutrition.

Interpretation: Estimation of the PAF of TB related to undernutrition is methodologically valid and operationally relevant, rather than PAF related to undernourishment, and should be used for future Global TB reports by WHO. Addressing undernutrition, the leading driver of TB in high TB burden countries (especially Asia) could enable achievement of END TB milestones of TB incidence for 2025.

Keywords: Global TB report; Population attributable fraction; Tuberculosis; Undernourishment; Undernutrition.

Fig. 1

Differentiating undernourishment and undernutrition. Legend: Undernourishment is defined by FAO as chronic food insecurity with food intake insufficient to meet basic energy requirements. Undernutrition is a physiological state resulting from insufficient intake or utilization of food, reflected in heights and weights below the lower limits of the ranges established for healthy people.

Fig. 2

Steps in arriving corrected and revised estimates of Population Attributable Fraction of undernutrition for TB.

Fig. 3

Number of cases of tuberculosis (in thousands) based on current, corrected and revised population attributable fraction (PAF) related to undernourishment and undernutrition in 30 high TB burden countries. TB incidence: Reported incidence in the Global TB Report 2020. Current: Number of cases of TB based on prevalence of undernourishment (by Food and Agriculture Organization) and relative risk of 3.2 as per the Global TB Report 2020. Corrected: Number of cases of TB based on prevalence of undernutrition (Global Health Observatory) and relative risk of 3.2. Revised: Number of cases of TB based on prevalence of undernutrition (Global Health Observatory figures) and revised relative risk of 4.49.