Interferon-gamma release assays piloted as a latent tuberculous infection screening tool in Canadian federal inmates

Int J Tuberc Lung Dis. 2014 Jul;18(7):787-92. doi: 10.5588/ijtld.13.0816.


Background: Interferon-gamma release assays (IGRAs) may be useful in diagnosing latent tuberculous infection (LTBI) in inmates; however, published experience in these settings is limited.

Objective: To identify variables associated with IGRA positivity among Canadian federal inmates with positive tuberculin skin test (TST) results.

Design: On intake, TST-positive (≥10 mm) inmates were offered an IGRA (QuantiFERON(®)-TB Gold), and demographic and historical data were collected. IGRA-positive and -negative inmates were compared using the χ(2) test and multivariable logistic regression; the final model's goodness of fit was assessed using Hosmer-Lemeshow test and area under the receiver operating characteristic curve (AUC).

Results: Of 96 TST-positive inmates, 31 (32.3%) were IGRA-positive. Variables associated with positive IGRA were age >45 years (11/20 vs. 20/75, P = 0.016) and previous LTBI treatment (9/20 vs. 13/55, P = 0.032) in univariate analysis, and being from a country with a moderate or high estimated tuberculosis (TB) incidence (OR 3.5, 95%CI 1.3-9.4, P = 0.013) and absence of bacille Calmette-Guérin (BCG) vaccination (OR 3.3, 95%CI 1.2-9.0, P = 0.017) in multivariable analysis. The data fit the model well, classifying the group better than chance alone (AUC 0.67, P = 0.007).

Conclusion: High discordance with TST, particularly among BCG-vaccinated inmates and those from low TB incidence countries, suggest that IGRA may be useful in Canadian federal penitentiary screening programmes.

MeSH terms

  • Adult
  • BCG Vaccine / administration & dosage
  • Canada
  • Humans
  • Interferon-gamma Release Tests*
  • Latent Tuberculosis / diagnosis*
  • Latent Tuberculosis / epidemiology
  • Logistic Models
  • Male
  • Mass Screening / methods
  • Middle Aged
  • Multivariate Analysis
  • Pilot Projects
  • Prisoners / statistics & numerical data*
  • Prisons*
  • Tuberculin Test


  • BCG Vaccine