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


METHODS
Between 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 >10 mm or if TST >/= 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 >/= 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.


CONCLUSIONS
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.
Tripodi
Dominique
D
Department of Occupational Medicine and Occupational Hazards, University Hospital of Nantes, France. Dominique.Tripodi@chu-nantes.fr.
Brunet-Courtois
Benedicte
B
Nael
Virginie
V
Audrain
Marie
M
Chailleux
Edmond
E
Germaud
Patrick
P
Naudin
Frederique
F
Muller
Jean-Yves
JY
Bourrut-Lacouture
Martine
M
Durand-Perdriel
Marie-Henriette
MH
Gordeeff
Claire
C
Guillaumin
Guyonne
G
Houdebine
Marietherese
M
Raffi
Francois
F
Boutoille
David
D
Biron
Charlotte
C
Potel
Gilles
G
Roedlich
Claude
C
Geraut
Christian
C
Schablon
Anja
A
Nienhaus
Albert
A