High yield from repeated testing for tuberculosis among high-risk citizens in Denmark

Evaluating stratified T-SPOT.TB results for diagnostic accuracy in tuberculosis disease: a retrospective cohort study with sensitivities, specificities, and predictive values

OBJECTIVES

The study aimed to investigate the association between quantitative T-SPOT.TB values and the risk of incident and prevalent tuberculosis disease (TBD), identify risk factors, and evaluate test accuracy.

METHODS

This retrospective cohort study followed patients tested consecutively with T-SPOT.TB at Aarhus University Hospital from 2010 to 2017, with follow-up for incident TBD through 2022. Data on demographics, comorbidities, medications, and TB status were collected from patient records and national registries. Cox proportional hazard models with restricted cubic splines assessed the risk of incident TBD (occurring ≥3 months post-test) by quantitative spot counts. Cox and log-binomial regressions identified risk factors for incident and prevalent TBD (occurring between 3 months before and after the test). Sensitivity, specificity, and predictive values assessed test accuracy. T-SPOT.TB was the index test, and microbiologically and/or clinically confirmed TBD was the reference standard.

RESULTS

Among 8542 individuals with complete follow-up, 59 developed incident TBD over 67 456 person-years. Among 9014 individuals tested once, 162 had prevalent TBD at the time of testing. The risk of incident TBD increased with higher spot counts, plateauing for tests with more than ten spots. The strongest risk factors for both incident and prevalent TBD were categorical T-SPOT.TB results: compared with negative tests (≤4 spots), adjusted hazard ratios for incident TBD were 5.0 (95% CI: 1.9-13.1) for borderline (5-7 spots) and 8.0 (95% CI: 4.0-15.7) for positive tests (≥8 spots). Adjusted risk ratios for prevalent TBD were 14.9 (95% CI: 7.7-28.9) for borderline and 35.6 (95% CI: 21.4-59.2) for positive tests. Sensitivities for incident and prevalent TBD were 54.0% (95% CI: 39.3-68.2%) and 78.4% (95% CI: 71.3-84.5%), respectively. Specificities were 84.8 (84.0-85.4) and 83.7 (82.9-84.4), respectively.

DISCUSSION

Incident TBD risk increases with T-SPOT.TB values but plateaus beyond 10 spots. Borderline and positive T-SPOT.TB results are strongly linked to TBD risk.

A cohort study of the long-term outcome of latent tuberculosis infection among socially marginalized people in a low-incidence country

BACKGROUND

Tuberculosis (TB) prevalence is high among socially marginalized citizens in Denmark, and management of latent TB infection (LTBI) may be part of preventing new cases. Patients with LTBI are offered either preventive treatment (TPT) or follow-up chest x-rays, but knowledge about the long-term outcome in terms of active TB is sparse.

METHODS

We performed a retrospective cohort study investigating the long-term outcomes for socially marginalized citizens who were diagnosed with LTBI or who had a positive interferon-gamma release assay (IGRA) but were lost to follow-up. Information on TB examinations, diagnostics, and treatment along with data on death were gathered from medical records from the date of positive IGRA to February 1, 2021.

RESULTS

We identified 119 patients with LTBI, 18 of which (15.1%) were diagnosed with TB during the follow-up period (mean, 4.5 years). TPT was completed by 36.1% and the TB incidence rate ratio of those completing TPT to those who did not was 0.78 (confidence interval, 0.25-2.17; P =.6). Of the patients with TB, 16 of 18 achieved treatment success.

CONCLUSION

High rates of TB development are found among socially marginalized citizens with LTBI. Overall incidence of TB was not significantly reduced by administration of TPT, although TB did not develop in the first 2 years following TPT.

Social determinants of tuberculosis: a nationwide case-control study, Denmark, 1990-2018

BACKGROUND

The global vision is a world free of tuberculosis (TB). Even in resource-rich TB low-incidence settings, we need more focus on the role of social risk factors to end the TB epidemic.

METHODS

Nationwide, retrospective register-based, case-control study from 1990 to 2018, including all TB patients in Denmark ≥18 years old (n = 9581) matched 1:3 on sex and age with population controls. TB risk factors were assessed in logistic regression models and estimated by odds ratio (OR).

RESULTS

All TB patients had considerably lower socio-economic status compared with controls (P < 0.0001). Among ethnic Danes, TB was mostly found among males, persons between 35 and 65 years, those living alone, those with low educational level, persons on social welfare benefits and those with low income. Conversely, for migrants, being younger, sex and living alone were less important, whereas having children was protective. In an adjusted multivariable regression model among Danes, key risk factors for TB were being on disability pension (OR = 2.7) and cash benefits (OR = 4.7). For migrants, fewer social risk factors increased TB risk, although low income and cash benefits did (OR = 3.1).

CONCLUSION

Even today in a resourceful setting, socio-economic status drives disparities in health. In our study, multifactorial social deprivation was highly associated with TB. Especially household structure, education, employment and income were important risk factors that should be addressed in the future to accelerate TB control and end the TB epidemic.