The feasibility of the interferon gamma release assay and predictors of discordance with the tuberculin skin test for the diagnosis of latent tuberculosis infection in a remote Aboriginal community

PLoS One. 2014 Nov 11;9(11):e111986. doi: 10.1371/journal.pone.0111986. eCollection 2014.

Abstract

Background: The tuberculin skin test (TST) is the standard test used to screen for latent TB infection (LTBI) in the northern Canadian territory of Nunavut. Interferon gamma release assays (IGRA) are T cell blood-based assays to diagnose LTBI. The Bacillus Calmette-Guerin (BCG) vaccine is part of the routine immunization schedule in Nunavut. The objective of this study was to test the feasibility, and predictors of discordance between the Tuberculin Skin Test (TST) and the IGRA assay in a medically under-serviced remote arctic Aboriginal population.

Methods: Both the TST and QuantiFERON-TB Gold (Qiagen group) IGRA tests were offered to people in their homes as part of a public health campaign aimed at high TB risk residential areas in Iqaluit, Nunavut, Canada. Feasibility was measured by the capacity of the staff to do the test successfully as measured by the proportion of results obtained.

Results: In this population of predominantly young Inuit who were mostly BCG vaccinated, the use of IGRA for the diagnosis of LTBI was feasible. IGRA testing resulted in more available test results reaching patients (95.6% vs 90.9% p = 0.02) but took longer (median 8 days (IGRA) vs 2 days (TST), p value < 0.0001). 44/256 participants (17.2%) had discordant results. Multivariable regression analysis suggested that discordant results were most likely to have received multiple BCG vaccinations (RR 20.03, 95% CI, 3.94-101.82)), followed by BCG given post infancy (RR 8.13, 95% CI, 2.54-26.03)) and then to a lesser degree when BCG was given in infancy (RR 6.43, 95% CI, 1.72-24.85).

Interpretation: IGRA is feasible in Iqaluit, Nunavut, a remote Arctic community. IGRA testing results in more test results available to patients compared to TST. This test could result in fewer patients requiring latent TB treatment among those previously vaccinated with BCG in a region with limited public health human resources.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Feasibility Studies
  • Female
  • Humans
  • Interferon-gamma Release Tests / methods*
  • Inuits
  • Latent Tuberculosis / diagnosis*
  • Male
  • Nunavut
  • Tuberculin Test / methods*
  • Young Adult

Grant support

The Public Health Agency of Canada, The National Lung Health Framework. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Nunavut Tunngavik Inc. did not provide support in the form of salaries and did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this authors is articulated in the ‘author contributions’ section.