Model says Canada will miss TB reduction goal among foreign-born

Tuberculosis remains concentrated among people born outside Canada: although foreign-born individuals make up about a quarter of the country’s population, they account for roughly three-quarters of active tuberculosis cases. New arrivals to Canada are screened for active TB disease but are generally not screened for latent TB infection (LTBI), so the hidden pool of people with LTBI living in Canada has been difficult to measure. To examine this problem, researchers led by corresponding author Jeremy Chiu developed a mathematical, population-level model that separates people into categories of actively infected, latently infected, and uninfected. Their approach uses reported data on TB incidence and prevalence in Canada to tune unknown parameters, and then compares model outputs to independent estimates, including an estimate of LTBI prevalence among immigrants entering Canada. By fitting the model to observed Canadian reports and validating it against other estimates, the team aimed to quantify how immigration and the existing population with LTBI together shape future TB burden among foreign-born Canadians.

The study uses an SEIR-compartment model that explicitly distinguishes latent TB infection (LTBI) from active disease and from those not infected. Unknown model parameters were calibrated to Canadian reports on the incidence and prevalence of active TB, and the model was validated by comparing computed quantities to other estimates of tuberculosis burden among foreign-born Canadians, including an estimate of the prevalence of LTBI among immigrants entering Canada. Using these calibrated and validated model runs, the researchers forecasted TB incidence through 2035 under scenarios that keep the number and profile of incoming immigrants similar to the past decade or eliminate new immigration altogether. The key findings are stark: if immigration continues as in the last decade, the model predicts Canada will not meet the WHO End TB 2035 goal of a 90% reduction in incidence compared to 2015 among the foreign-born population. Even in a scenario with no new immigrants, the model still predicts failure to reach the incidence goal, driven primarily by activation of LTBI already present in foreign-born Canadians. The results held regardless of the WHO geographic region from which immigrants originate.

These results highlight the importance of the latent TB reservoir among foreign-born Canadians for Canada’s ability to reach international TB reduction targets. Because the model shows that activation of LTBI in people already in Canada could prevent achieving the WHO End TB 2035 incidence goal even without new arrivals, the study suggests that attention to LTBI prevalence and its management is central to long-term TB control. The work does not prescribe a single policy, but it provides evidence that current screening focused mainly on active disease may miss a substantial driver of future cases. For public health planners and policymakers, the model offers a quantitative tool to explore how different strategies targeting LTBI among foreign-born populations could change projected incidence. In short, without addressing the hidden pool of LTBI, meeting the End TB 2035 target among foreign-born Canadians appears unlikely according to this modeling study led by Jeremy Chiu and colleagues.