Evaluation of the tuberculin skin test and the interferon-gamma release assay for TB screening in French healthcare workers

IntroductionUsing French cut-offs for the Tuberculin Skin Test (TST), results of the TST were compared with the results of an Interferon-gamma Release Assay (IGRA) in Healthcare Workers (HCW) after contact to AFB-positive TB patients.MethodBetween May 2006 and May 2007, a total of 148 HCWs of the University Hospital in Nantes, France were tested simultaneously with IGRA und TST. A TST was considered to indicate recent latent TB infection (LTBI) if an increase of more 10mm or if TST (greater than or equal to) 15 mm for those with no previous TST result was observed.

For those with a positive TST, chest X-ray was performed and preventive chemotherapy was offered.

Results: All HCWs were BCG-vaccinated. The IGRA was positive in 18.9% and TST (greater than or equal to)10 mm was observed in 65.5%.

A recent LTBI was believed to be highly probable in 30.4% following TST. Agreement between IGRA and TST was low (kappa 0.041).

In 10 (16.7%) out of 60 HCWs who needed chest X-ray following TST the IGRA was positive. In 9 (20%) out of 45 HCWs to whom preventive chemotherapy was offered following TST the IGRA was positive.

Of those considered TST-negative following the French guidelines, 20.5% were IGRA-positive. In a two-step strategy - positive TST verified by IGRA - 18 out of 28 (64.3%) IGRA-positive HCWs would not have been detected using French guidelines for TST interpretation.

Conclusion: The introduction of IGRA in contact tracings of BCG-vaccinated HCWs reduces X-rays and preventive chemotherapies.

Increasing the cut-off for a positive TST does not seem to be helpful to overcome the effect of BCG vaccination on TST.

Author: Dominique TripoldiBenedicte Brunet-CourtoisVirginie NaelMarie AudrainEdmond ChailleuxPatrick GermaudFrederique NaudinJean-Yves MullerMartine Bourrut-LacoutureMarie-Henriette Durand-PerdrielClaire GordeeffGuyonne GuillauminMarie-Therese HoudebineFr

Published on: 2009-11-30

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