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Repeat IGRA testing in Canadian health workers: conversions or unexplained variability?

Alice Zwerling1, Andrea Benedetti, Mihaela Cojocariu

  • 1Department of Epidemiology, Biostatistics & Occupational Health, McGill University, Montreal, Canada.

Plos One
|February 6, 2013
PubMed

Insights

Healthcare workers showed higher than expected interferon-gamma release assay (IGRA) conversions, but these did not correlate with occupational tuberculosis (TB) exposure. Tuberculin skin testing (TST) showed no conversions, suggesting IGRA changes may not indicate new TB infection.

Area of Science:

  • Occupational Health
  • Infectious Disease Epidemiology
  • Diagnostic Test Evaluation

Background:

  • North American hospitals are transitioning from tuberculin skin testing (TST) to interferon-gamma release assays (IGRAs) for latent tuberculosis infection (LTBI) screening.
  • Limited data exist on the association between occupational exposure and serial IGRA results in healthcare workers (HCWs).

Purpose of the Study:

  • To evaluate serial QuantiFERON-TB Gold In-Tube (QFT) results in Canadian healthcare workers (HCWs) and assess their correlation with occupational tuberculosis (TB) exposure.

Main Methods:

  • A cohort of 258 Canadian HCWs underwent serial TST and QFT testing over one year.
  • Conversion and reversion rates for both tests were calculated.
  • Correlation between test results and reported recent TB exposure was analyzed.

Main Results:

  • A QFT conversion rate of 5.3% was observed among HCWs with an initial negative QFT.
  • No TST conversions occurred in HCWs with an initial negative TST.
  • No association was found between recent TB exposure and QFT conversions.

Conclusions:

  • The study observed a higher-than-expected rate of QFT conversions using standard definitions.
  • Observed QFT 'conversions' in HCWs may not represent new TB infections, as they were not linked to occupational exposure.
  • Serial IGRA testing warrants further investigation regarding its interpretation in occupational settings.
Abstract

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