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15 September 2020

With tuberculosis the biggest infectious disease killer in the world, countries often need to better target scarce funding to combat the disease effectively.

Travelling to nations ranging from Bulgaria to Bhutan, members of the Australian Tuberculosis Modelling Network (AuTuMN) provide information that is helping guide national policies for managing and treating the highly infectious disease.

Prof Emma McBryde, Director of AuTuMN and an infectious diseases physician, explains they are assisting the Global Fund inform managers of national TB control programs about how the money can most effectively be spent. The five main countries the network is working with include Mongolia, Fiji and the Philippines.

Prof McBryde says in those countries they work directly with national TB program managers, who are the experts and become co-producers of the documents. Through third parties, the network also contributed to multi-modelling exercises for TB control in India, China, South Africa, Papua New Guinea and Uzbekistan.  

A Professorial Research Fellow in infectious diseases and epidemiology at AITHM, Prof McBryde says: ‘So it's partly health economics, but it's also party understanding a bit more about TB dynamics, because most countries think that they can reach their end TB goals, by continuing business as usual, maybe doing it a little bit better. But we often have to show them that in fact that they're not going to reach their targets doing the same things that they've always done, even if they do them extremely well.

Across the world around 1.45 million people died of TB in 2018.The Global Fund reported that despite ‘remarkable improvements’ in efforts to find and treat infected people, the percentage of people with TB who are ‘missed’ by health systems still stood at around 30 percent.

The Global Fund provides almost 70% of all international funding for TB, including US$9.5 billion for TB/HIV programs. Prof McBryde says each country has to prepare a business case for how the money will be spent. AuTuMN is employed by the fund to do modelling which can assist countries evaluate and improve the efficiency of current spending and better allocate future funding for TB control.

Prof McBryde’s modelling group turned its attention to tuberculosis in 2012, with the first transmission dynamic model of TB for the Asia Pacific in 2012. Recently the core model was refined to ‘include all sorts of different risks – so we’ve now got a really flexible, modular system depending on what the country is interested in.’

For example, in Papua New Guinea it was important to focus on multi-drug resistant TB. ‘But then in Uzbekistan we had to think about [extensively drug resistant] XDR-TB, that was resistant even to second-line agents, because that was what they were trying to avoid.’

They can factor HIV into the model for countries such as South Africa or trim it right back in countries like Fiji, where HIV is not a major driver of TB

In some countries the AuTuMN team have suggested extending coverage to latent TB cases. She explains: ‘in terms of bang for your buck reducing morbidity, you can go a lot further treating latent TB, because there’s so much more of it.’

To cross-validate that they may suggest a prevalence survey where they test thousands of people to work out what proportion of people have active TB that is either dormant or undiagnosed. Sometimes prevalence surveys come along and countries realise they’re missing half their cases.

‘Often, sadly our models suggest there's quite a bit more mortality from TB than the country expected.’ In Fiji, they cross triangulated death register information with the National TB Register and confirmed that there was a lot of under reporting.

Ironically when effective TB programs are implemented, considerably more people with the TB are detected and treated. Prof McBryde says: ‘Initially it makes the TB statistics look worse… It's not until between five and 10 years that you'll actually see a dent in TB epidemic and start having reduced burden on the TB program.’

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