Tuberculosis (TB) remains a significant global public health challenge and is the largest cause of infectious disease death globally. Poverty and undernutrition are strongly linked to TB burden, and low-middle income countries (LMICs), such as India, suffer a greater global proportion of TB incidence and mortality. Unfortunately, efforts to reduce the TB burden can be hampered by events impacting the global food system, including, in more recent times, infectious disease pandemics and international wars which can cause changes to energy prices and restrictions to exports. Clark and colleagues from the London School of Hygiene and Tropical Medicine used mathematical modelling to predict and simulate the changes in TB incidence and mortality in India as a consequence of nutritional shocks to the food system generated from such global events.
What inspired the study?
The World Health Organisation (WHO) developed an End TB Strategy that aims to reduce TB incidence by 80%, TB deaths by 90%, and to eliminate catastrophic costs for TB-affected households by 2030 [1]. Currently, most countries are not on track to meet these goals. A small, but not insignificant factor contributing to this may be nutritional shocks to the global food system from indirect environmental and social events. These often distal nutritional shocks can have rippling effects and ramifications on TB incidence and mortality, by increasing the proportion of the population with undernutrition, leading to an increase in the risk of developing TB. [2,3] The authors used a TB infection transmission model coupled with the LandSyMM food system model [4] to estimate the consequences of such nutritional shocks on the burden of TB to highlight their impact and the importance of considering additional preventative measures to reduce the TB burden.
Why is it important?
The findings help policy-makers and researchers to better appreciate that the impact of external, uncontrollable factors (for example, changes in energy prices and export restrictions resulting from external events such as global pandemics or war) can be wide reaching. In the case of TB, it is important to consider how impacts on food systems may influence undernutrition in a population, and the need for additional interventions to prevent the negative consequences. Importantly, in the worst-case scenario where the nutritional shock to the global food system is more severe (as modelled by Clark et al), the consequences on TB-related incidence and mortality in India could be significant over the next decade.
Did this study show anything unexpected?
Model estimates demonstrated that the TB burden may be influenced by nutritional shocks from environmental and social events. The impact of nutritional shocks on the TB burden is perhaps not unexpected, yet the authors empirical approach to the question has revealed alarming consequences. The findings indicated that nutritional shocks in the worst-case scenario, with both increases in energy prices and export restrictions, could increase the TB incidence and mortality rates by 5.0% and 4.9%, respectively, in India in 2035, and lead to an additional 1.1 million TB episodes and 177.5 thousand deaths between 2022–2035.
What is the wider significance of the study findings?
These findings highlight the importance of worldwide interactions and cascading risks on food security, which potentially have detrimental influences on attempts to end TB in India and globally through increasing undernutrition. The authors indicate that the impact of crises on TB may be underappreciated if the impact on nutrition is not considered. The implications are significant for guiding future research efforts and for informing policy makers in high TB burden countries about the importance of nutritional shocks when monitoring TB incidence and mortality.
References:
World Health Organization. WHO | WHO End TB Strategy. 2015.
World Health Organization. Global tuberculosis report. 2024.
Bhargava A, et al. Attributable is preventable: corrected and revised estimates of population attributable fraction of TB related to under-nutrition in 30 high TB burden countries. J Clin Tuberc Mycobact Dis.2022;27:100309.
Landsymm. https://landsymm.earth/. Accessed 19 Dec 2023.