Focused screening of new residents, key to fight TB in Canada

New study provides unique data on tuberculosis infection rates among foreign-born Canadian residents and citizens

Montreal, December 13, 2023—According to the World Health Organization (WHO), tuberculosis (TB) caused 1.3 million deaths in 2022 and is still very much present in many countries. In Canada, where foreign-born residents bear 80 per cent of the burden of TB, the annual incidence rate is close to 5 cases per 100,000 persons, far from the WHO’s goal to reduce it to one case per million inhabitants.

A new study by researchers at the Research Institute of the McGill University Health Centre (RI-MUHC) found that approximately one in four foreign-born Canadian residents is infected with TB, but very few of them were infected within the last two years, the period of highest risk for progression to the active form of the disease. The authors of the study funded by the Canadian Institutes of Health Research and newly published in CMAJ suggest that prevention strategies should prioritize infection screening for new permanent residents from countries where the incidence of TB is high. It would be costly and ineffective to test people who have been in the country for more than two years.

“According to the World Health Organization, 5–10 per cent of people infected with TB develop the disease in their lifetime. However, the risk of developing TB disease is 25–50 times higher within the first two years of acquiring the infection compared to when more years have elapsed,” explains Dr. Kevin Schwartzman, senior scientist in the Translational Research in Respiratory Diseases Program at the RI-MUHC, professor of Medicine at McGill University and co-senior author of the study. “Our study suggests that among all foreign-born Canadian residents infected with TB in 2021, only 1 in 488 were infected in the two years prior, with increased risk of developing TB disease.”

“Preventive treatment of tuberculosis is highly effective in preventing the development of the disease in infected individuals. However, implementing widespread screening and treatment programs for TB infection would likely be prohibitively expensive and would mean treating a very large number of people at very low risk of developing disease,” adds Jonathon Campbell, PhD, junior scientist in the Translational Research in Respiratory Diseases Program at the RI-MUHC, assistant professor in the Department of Medicine at McGill University and co-senior author of the study. “We conducted this study to help identify groups for whom screening would be more effective and would likely detect greater proportions of infections.”

A clearer picture of the situation

Based on the results of the study, the estimated overall prevalence of TB infection among foreign-born people in Canada was 25 per cent for the 2001 census year, 24 per cent for 2006, 23 per cent for 2011, 22 per cent for 2016 and 22 per cent for 2021, close to the global average of 23 per cent. The researchers also observed that prevalence increased with age at migration and the incidence of TB in the country of origin.

Provincially, the estimated prevalence of infection in 2021 among foreign-born residents was lowest in Quebec (19%) and highest in Alberta (24%) and British Columbia (24%).

To produce these results, the researchers synthesized information about TB disease and infection rates in all countries of the world, over the past 90 years, to estimate how likely it is that people living in any given country were exposed to and infected with TB at any given year. They linked this data to information from Canadian censuses, including the number of people living in Canada who came from each country, as well as their age and time spent in Canada. Their work revealed that foreign-born Canadian residents with TB infection were likely infected long before they migrated, and therefore most are at low risk of developing the disease.

Progressing towards TB elimination

The authors of the study point out that, despite Canada’s previous target of reducing the incidence of TB in Canada to 3.5 cases per 100,000 population by 2015, it remained at 4.8 per 100,000 in 2021. This, despite the fact that Canada and the global community have agreed to end TB by 2030, as part of United Nations’s Sustainable Development Goals. The authors attribute the lack of progress towards TB elimination over the last decade to epidemiological changes and the lack of prevention strategies.

 “Our study provides much needed estimates and information on TB infection among foreign-born people living in Canada. We hope that it informs clinical and policy-level decision-making,” says Aria Jordan, first author of the study and former master’s student under Dr. Schwartzman.

About the study

The study The prevalence of tuberculosis infection among foreign-born Canadians: a modelling study was conducted by Aria Ed Jordan, Ntwali Placide Nsengiyumva, Rein M. G. J. Houben, Peter J. Dodd, Katie D. Dale, James M. Trauer, Justin T. Denholm, James C. Johnston, Faiz Ahmad Khan, Jonathon R. Campbell and Kevin Schwartzman.

DOI: https://doi.org/10.1503/cmaj.230228

About the Research Institute of the McGill University Health Centre

The Research Institute of the McGill University Health Centre (RI-MUHC) is a world-renowned biomedical and healthcare research centre. The institute, which is affiliated with the Faculty of Medicine of McGill University, is the research arm of the McGill University Health Centre (MUHC)—an academic health centre located in Montreal, Canada, that has a mandate to focus on complex care within its community. The RI-MUHC supports over 450 researchers and around 1,200 research trainees devoted to a broad spectrum of fundamental, clinical and health outcomes research at the Glen and the Montreal General Hospital sites of the MUHC. Its research facilities offer a dynamic multidisciplinary environment that fosters collaboration and leverages discovery aimed at improving the health of individual patients across their lifespan. The RI-MUHC is supported in part by the Fonds de recherche du Québec—Santé (FRQS). rimuhc.ca

Media contact

Fabienne Landry
Communications coordinator, Research, MUHC
[email protected]