Our work has shown not just that there are different states of TB disease, but also how important these states are, with around half of infectious individuals not reporting symptoms (Figure 1), what happens after people become infected (Figure 2), and how relevant these states are for transmission (Figure 3).
To do this, we looked at all relevant data from 1905 until now, and put those together in a single modelling framework. We looked at what were the most likely states and disease pathways to fit the data, and then put it all together in a single framework to understand how people experience TB disease. Our results show that only 10% of people who are infected develop TB, and the majority of those who do not progress to disease actually clear their infection instead of remaining at risk lifelong (Figure 2). If someone gets disease, only a third will develop classic disease where an individual both has symptoms and is infectious. The remainder will have tissue damage and may be infectious, but either remain in that state or recover after a long period. Because of that, around half of transmission comes from people who either never develop classic disease, or are yet to do so.
In our final pieces of work we are looking at how these new insights change the likely impact and cost of current and potential future TB policies, in terms of finding and treating people with TB. We found that current approaches, where people with TB have to report to clinics before they receive care, do not interrupt transmission, which explains why we still see so much TB, even if fewer people die from the disease. Instead, if we screen people regardless of symptoms, we can quickly reduce new infections occurring.
We also contributed our experience to the COVID-19 response by estimating how much of SARS-CoV-2 transmission was due to non-symptomatic individuals using data from the outbreak on the Diamond Princess cruise ship (Figure 4). We showed that non-symptomatic transmission was a major issue during the pandemic, which was confirmed by other work.
To make our results as useful as possible, we have presented our work at scientific conferences, but also focussed on discussions with those who decide on global policy (World Health Organisation), funding for product development and research (Bill and Melinda Gates Foundation, Wellcome Trust) and global research groups. We also organised a large consensus meeting with people from across professions, countries and lived TB experience to set a new framework for describing and researching TB.
For more information and related publications, please see:
https://erc-tbornottb.github.io/(opens in new window)
