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Can a Risk Prediction Tool Eliminate Tuberculosis from Canada?

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In 2018, the UN convened its first ever conference to discuss the global tuberculosis (TB) epidemic. TB remains the leading cause of single-infection deaths in the world, with approximately 1.5 million deaths and 10 million new infections globally, surpassing both HIV and Malaria. Leading scientists from around the world gathered in New York City in 2018 to develop an action plan to eliminate this entirely treatable disease. They called for a 95% reduction in TB deaths by 2035.

Drs. Joseph Puyat and James Johnston

In response to this call to action, Dr. James Johnston from the BC Centre for Disease Control (BCCDC) and CHÉOS Scientist Dr. Joseph Puyat are working to develop a risk prediction tool to better screen populations in Canada at high risk of developing TB. To understand their novel approach, let’s look first at the underlying causes of TB and the best course of action to address it.

TB is a bacterial infection caused by Mycobacterium tuberculosis. This bacterium is highly contagious and typically manifests in the lungs through air-borne transmission. The bacteria replicate very slowly — for some, symptoms do not start to appear until years after the initial infection, while others are able to suppress it and can live with it their whole lives without any complications. Experts estimate that up to 20% of the global population are living with a latent TB infection, while 10% of those case develop into an active infection. Only those with an active infection, however, are able to pass it on.

Certain populations present a higher risk of developing active TB. The World Health Organization (WHO) lists certain diseases, especially HIV, diabetes and kidney disease, that put patients at a higher risk of developing an active infection. Yet, the majority of new infections occur in the developing world, indicating that proper sanitation, hygiene and access to medical care are the best preventative measures against the disease.

Canada has done extremely well at slowing the number of TB cases since the end of the second world war. With the introduction of antibiotics, as well as the development of better screening techniques, TB rates fell to only 1,200 cases across the country in 2017. The majority of these cases, approximately 70%, presented in newcomers who likely contracted the disease in their country of origin before arriving in Canada. With over 1 million foreign-born residents in BC alone, testing that many people would be a herculean task. Moreover, screening can cost up to $500 per test and requires several follow-up appointments. By properly determining who should be screened and who should not, we may well be able to work towards eliminating active TB infections in Canada.

With these statistics in mind, Dr. Johnston and Dr. Puyat are working to develop a risk prediction tool that will help health authorities know who is most at risk. “It’s not that we aren’t testing enough people,” says Dr. Johnston, “it’s that we’re testing the wrong ones.” These experts believe that TB testing for people arriving from high-incidence countries who present certain other risk factors, such as diabetes or close contact with someone who had an infection, could significantly reduce the number of cases in Canada. If a newcomer tests positive they can immediately be put on a course of preventative therapy, which reduces the instance of an active infection by 95%.

With big data, Dr. Puyat and Dr. Johnston believe they can better direct resources towards those who need it. Using linked health administrative data sets from BC between 1985 and 2015, they analyzed historical trends to determine the characteristics of someone at risk. This includes demographic data, such as age, sex and country of origin, as well as the risk factors identified by the WHO. This historical data are being used to develop a risk prediction tool, and once it proves to be reliable and accurate they will be able to put it into action to instantaneously determine who falls within the ‘high risk’ category and should be tested upon arrival.

More and more, big data is becoming a tool for assessing health outcomes and predicting into the future. As scientists at CHÉOS and the BCCDC continue to develop tools like TB risk prediction, they move us one step closer towards seeing the eradication of diseases that have affected humans throughout history.

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