Tuberculosis and Immigration: Understanding Risks and Future Trends

Tuberculosis (TB) remains a significant global health challenge. In 2024, an estimated 10.7 million people developed TB, and approximately 1.23 million died from the disease . While TB can initiate as an asymptomatic infection, it can progress to an active, infectious disease at any time. Understanding the interplay between TB and immigration patterns is crucial for effective public health strategies.

TB Infection vs. Active Disease

TB infection, diagnosed through immunoreactivity tests (skin tests or interferon-γ release assays) , doesn’t always mean someone has active TB disease. Immunoreactivity indicates exposure to the TB bacteria, but doesn’t confirm active illness. A key challenge is distinguishing between recent infections (high risk of progression) and remote infections (lower risk). The risk of developing TB is highest within the first two years after infection .

Immigration and TB Risk

In many low-incidence countries, TB disproportionately affects immigrant populations due to the progression of latent TB infections acquired in higher-transmission settings before immigration . This has led to the implementation, or consideration of, large-scale TB infection screening and treatment programs for new immigrants . The cost-effectiveness of these programs depends on the prevalence of TB immunoreactivity and the likelihood of developing active TB disease.

New Research on TB and Immigration

A recent study investigated how changing TB epidemiology affects TB immunoreactivity prevalence and the risk of developing TB disease among new immigrants to low-incidence countries. Researchers analyzed data from 168 countries, focusing on immigrants from India, China, the Philippines, and Vietnam – common countries of origin for immigrants to Canada, the United States, the United Kingdom, and Australia .

Key Findings:

• Declining ARI: The annual risk of infection (ARI) is decreasing in the studied countries, with estimates ranging from a 2% to 3% decline per year.
• Projected Prevalence: TB immunoreactivity prevalence is projected to decrease among immigrants from these countries by 2050. For example, prevalence among immigrants from the Philippines is expected to drop from 40.1% in 2024 to 23.0% in 2050.
• Recent vs. Remote Infection: The prevalence of recent TB infection (within the past two years) is relatively stable, but is more sensitive to changes in transmission rates.
• Age Matters: Younger immigrants are more likely to benefit from reduced TB transmission rates than older adults, who have had more cumulative exposure.
• Risk Reduction: Accelerating declines in ARI leads to greater reductions in TB risk, particularly by reducing the number of individuals with recent infections.

Implications for TB Screening Programs

The study suggests that the cost-effectiveness of immigration TB screening and treatment programs may decrease over time as TB prevalence and risk decline. This highlights the need for continuous evaluation and potential targeting of these programs to ensure efficient leverage of healthcare resources. As global TB incidence declines, the risk-benefit calculus of preventive treatment may also shift, potentially requiring more targeted approaches.

The J.D. MacLean Centre for Tropical & Geographic Medicine

The J.D. MacLean Centre for Tropical & Geographic Medicine at McGill University plays a vital role in addressing these challenges. The Centre provides medical care for returning travelers, immigrants, and refugees, with expertise in imported and parasitic infections . It also conducts research and training in tropical and geographically-restricted infectious diseases . Recent advancements from the Centre include the development of an ultra-rapid antimicrobial susceptibility testing device .

Looking Ahead

Continued monitoring of TB epidemiology and immigration patterns is essential for adapting public health strategies. Further research is needed to understand the long-term impact of reduced TB transmission on screening program effectiveness and to optimize targeted interventions for high-risk populations.