Cascade of tuberculosis transmission

Overview

Tuberculosis (TB) remains a global health problem with an immense disease burden, estimated at 10.4 million new cases in 2015. To stop the tuberculosis epidemic, we must interrupt TB transmission. Further, the interventions needed to interrupt TB transmission must be targeted to high-risk groups and environments. 

Tuberculosis Transmission Cascade 

In this article, a simple cascade for tuberculosis transmission is proposed. A source case of tuberculosis generates infectious particles that survive in the air and are inhaled by a susceptible individual who may become infected and then can develop tuberculosis. Interventions that target bacterial, host, or behavioural catalysts of transmission will interrupt tuberculosis transmission and accelerate the decline in tuberculosis incidence and mortality. A simple cascade for tuberculosis transmission is proposed in which a source case of TB generates infectious particles that remain in the air and are inhaled by a receptive individual who may get infected and who then has the potential to develop TB. Interventions that target such events will interrupt TB transmission and accelerate the decline in TB incidence and mortality. The purpose of this article is to provide a high-level overview of what is known about TB transmission, using the TB transmission cascade as a framework. In addressing and understanding these topics, we can understand what it will take to stop TB transmission.

The cascade of tuberculosis transmission proceeds in steps as follows:

1. Source the case: Individual with tuberculosis 

2. Aerosolization: Release of viable airborne bacilli

3. Airborne survival: Characteristics and factors associated with survival of Mycobacterium tuberculosis in air

4. Exposure and inhalation: Contact- name, duration, intensity, location

5. Infection, with the potential to progress the disease

It goes back to step1, and the cycle goes on.

Conclusion

In his Nobel Lecture, Robert Koch said that "amidst the persistently wide variety in the means and ways of combating tuberculosis, it is still necessary to ask what measures do indeed best satisfy the scientific requirements". Over 100 years later, and we are still asking the same question. Although our understanding of TB transmission has improved substantially, many gaps remain. 

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