1. Who
The study included 1,030,873 immigrants residing in British Columbia (BC), Canada, all of whom were born outside Canada and immigrated between January 1, 1985 and December 31, 2012, with follow-up through December 31, 2015.
Exposure groups
- TB diagnosed group: 2,435 individuals diagnosed with TB in BC with documented TB treatment completion
- Non-TB group: 1,028,438 individuals not diagnosed with TB in BC
Exclusion criteria
- Invalid TB diagnosis or death dates (before Jan 1, 1985)
- TB diagnosis without documented treatment completion (main analysis; included in sensitivity analyses)
- Missing covariate values (<5%)
- Post-mortem TB diagnoses
Participant characteristics
Compared with non-TB controls, TB patients were:
- Older
- Had more comorbidities
- Had lower socioeconomic status
- More likely from countries with high TB incidence
- More likely to have earlier immigration dates
Total follow-up:
13.5 million person-years
Total deaths:
26,376 deaths
- TB group: 285 deaths
- Non-TB group: 24,887 deaths
2. What
The study examined whether TB diagnosis increases long-term mortality risk from causes other than TB among immigrants living in BC.
Primary Outcome
Post-TB treatment mortality from non-TB causes
Measured as:
- Time from index date to non-TB death (person-years)
TB deaths were excluded using:
- ICD-9-CM: 011–018
- ICD-10-CA: A15–A19
Secondary Outcomes
Cause-specific mortality:
- Cardiovascular disease
- Respiratory disease
- Cancer
- Injuries/poisonings
Key Findings
Main Result
After full covariate adjustment:
Patients diagnosed with TB had:
aHR = 1.69
(95% CI: 1.50–1.91)
for non-TB mortality compared with those without TB.
This means:
69% higher long-term risk of non-TB death
Unadjusted result
HR = 4.01
(95% CI: 3.57–4.51)
Age/sex-adjusted result
aHR = 1.95
(95% CI: 1.74–2.20)
Cause-specific mortality increases
TB diagnosis was associated with:
- 196% higher respiratory mortality
- 63% higher cardiovascular mortality
- 40% higher cancer mortality
- 85% higher injury/poisoning mortality
Sensitivity Analysis
Including patients without treatment completion increased risk:
aHR = 2.05
showing even stronger mortality risk.
Subgroup Findings
Men had higher excess mortality than women.
Effect modification by immigration class:
- Refugee class: aHR = 1.4
- Economic: aHR = 2.4
- Family: aHR = 2.8
- Other: aHR = 2.5
Authors’ Conclusion
TB diagnosis is associated with substantially increased long-term mortality from non-TB causes, even after successful treatment completion.
This increased risk appears immediately after treatment completion and persists over time.
TB may function both as:
- A direct causal contributor to later morbidity/mortality
- A marker of broader vulnerability and chronic disease risk
Practical / Policy Implications
The authors recommend:
- Longer-term follow-up after TB treatment completion
- Integration of chronic disease prevention and management into TB care
- Reconsideration of TB prevention cost-effectiveness models to include long-term post-TB mortality
- Broader post-TB survivorship care in high-income settings
3. When
Study period
Immigration cohort:
1985–2012
Residence and mortality follow-up:
January 1, 1985 to December 31, 2015
Total follow-up:
13.5 million person-years
4. Where
The study was conducted in British Columbia (BC), Canada British Columbia.
This is a high-income healthcare setting with universal public health infrastructure.
5. Why
Most TB cases in BC occur among immigrants, and previous evidence suggests important differences in both TB epidemiology and mortality patterns between immigrants and Canadian-born populations.
Prior studies suggested higher mortality after TB, but evidence specifically evaluating non-TB mortality after TB treatment completion among immigrants was limited.
The authors aimed to determine whether TB increases long-term mortality beyond TB itself.
Hypothesis
Immigrants diagnosed with TB would have higher non-TB mortality risk than immigrants without TB.
6. How
Study Design
Retrospective population-based cohort study
Level of Evidence
Observational cohort study
→ stronger than cross-sectional studies for temporal associations, but still limited for causal inference
Exposure
Time-varying exposure:
TB diagnosis during residency in BC
Included:
- Clinically diagnosed TB
- Microbiologically confirmed TB
Required:
-
Documented treatment completion
(≥6 months standard anti-TB therapy)
Exposure time:
- Before TB diagnosis = unexposed
- After TB diagnosis = exposed
Only first TB diagnosis considered.
Covariates
Adjusted for:
- Age
- Sex
- Immigration class
- Country-of-origin TB incidence
- Education
- Neighborhood income quintile
- Charlson Comorbidity Index
- Year of immigration
- Socioeconomic and demographic variables
Statistical Analysis
Used:
Time-dependent Cox proportional hazards regression
Also:
- Kaplan–Meier survival curves
- Sensitivity analyses
- Sex-specific subgroup analyses
- Effect modification analyses
Major Limitations
Likely limitations include:
- Residual confounding despite adjustment
- Observational design cannot prove causality
- Possible healthy immigrant effect bias
- Exclusion of those dying during TB treatment in main analysis may underestimate risk
- Registry-based misclassification possible
