Understanding the mechanisms of climate change impact on tuberculosis: a complex systems approach

Tuberculosis (TB) is a leading cause of disability and mortality in many countries and is the leading cause of death from an infectious agent worldwide. While TB is a curable and preventable disease, health systems' ineffectiveness in case finding and appropriate treatment results in 10 million new cases and 1.5 million deaths annually around the globe. Climate change is expected to have a major impact on TB and other infectious diseases, although the mechanisms for this are still poorly understood.

We undertook a systematic review of Literature published up to September 2024 about the effects of climate Change on TB incidence. The review identified 35 papers that described possible mechanisms for the impact of climate change on TB. We used a complex systems approach called causal loop diagramming to integrate the identified mechanisms into a system map of climate change effects on TB. A panel of experts on TB, epidemiology, and climate change reviewed the map's structure and content.

The final map shows 6 reinforcing feedback loops and associated chains of complex bio-socio-technical interrelations through which climate change can affect TB risk. The loops included reciprocal relationships between heatwave - energy use, indoors time - airborne disease risk, food access - price, malnutrition - infectious disease, healthcare cost - detection delay, and infectious contact - TB risk that translate to TB infection, directly or indirectly, when activated.

The presented map illustrates and highlights the need for coordinated, multisectoral and complex interventions across that bio-socio-technical system to tackle the nexus of climate change and TB risk. In this context, identifying key leverage points and implementing strategic actions on these points are essential to effectively mitigate climate change-related risks and their impact on TB transmission and incidence.