title: Repeat IGRA testing in Canadian health workers: conversions or unexplained variability?
abstract: BACKGROUND
  Although North American hospitals are switching from tuberculin testing (TST) to interferon-gamma release assays (IGRAs), data are limited on the association between occupational exposure and serial QuantiFERON-TB Gold In-Tube (QFT) results in healthcare workers (HCWs).
  
  
  METHODS
  In a cohort of Canadian HCWs, TST and QFT were performed at study enrolment (TST1 and QFT1) and 1 year later (TST2 and QFT2). Conversion and reversion rates were estimated, and correlation with TB exposure was assessed.
  
  
  RESULTS
  Among 258 HCWs, median age was 36.8 years, 188/258 (73%) were female and 183/258 (71%) were Canadian-born. In 245 subjects with a negative QFT1 we found a QFT conversion rate of 5.3% (13/245, 95% CI 2.9-8.9%). Using more stringent definitions, QFT conversion rates ranged from 2.0 to 5.3%. No TST conversions were found among the 241 HCWs with negative TST1, and no measure of recent TB exposure was associated with QFT conversions. In the 13 HCWs with a positive QFT1, 62% reverted.
  
  
  CONCLUSIONS
  Using the conventional QFT conversion definition, we found a higher than expected rate of conversion. Recent occupational exposures were not associated with QFT conversions, and no TST conversions occurred in this cohort, suggesting the 'conversions' may not reflect new TB infection.
authors: Department of Epidemiology, Biostatistics & Occupational Health, McGill University, Montreal, Canada.
authors: Alice
authors: A
authors: Zwerling
authors: Andrea
authors: A
authors: Benedetti
authors: Mihaela
authors: M
authors: Cojocariu
authors: Fiona
authors: F
authors: McIntosh
authors: Filomena
authors: F
authors: Pietrangelo
authors: Marcel A
authors: MA
authors: Behr
authors: Kevin
authors: K
authors: Schwartzman
authors: Dick
authors: D
authors: Menzies
authors: Madhukar
authors: M
authors: Pai
mesh_terms: D000328:Adult; D002170:Canada; D015331:Cohort Studies; D005260:Female; D006282:Health Personnel; D006801:Humans; D059425:Interferon-gamma Release Tests; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D009169:Mycobacterium tuberculosis; D016273:Occupational Exposure; D012680:Sensitivity and Specificity; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis*; D055815:Young Adult
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