Research

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

Dominique Tripodi¹ , Benedicte Brunet-Courtois¹ , Virginie Nael¹ , Marie Audrain² , Edmond Chailleux³ , Patrick Germaud³ , Frederique Naudin⁴ , Jean-Yves Muller² , Martine Bourrut-Lacouture¹ , Marie-Henriette Durand-Perdriel¹ , Claire Gordeeff¹ , Guyonne Guillaumin¹ , Marietherese Houdebine¹ , Francois Raffi⁵ , David Boutoille⁵ , Charlotte Biron⁵ , Gilles Potel⁶ , Claude Roedlich¹ , Christian Geraut¹ , Anja Schablon⁷ and Albert Nienhaus⁷

¹  Department of Occupational Medicine and Occupational Hazards, University Hospital of Nantes, France

²  Department of Immunology, University Hospital of Nantes, France

³  Department of Pneumology, Laënnec Hospital, University Hospital of Nantes, France

⁴  Tuberculosis Public Health Clinic, 6 rue Hippolyte Durand Gasselin, Nantes, France

⁵  Department of the Infectious and Tropical illnesses, Hospital, CHU Nantes, France

⁶  Emergency Department, University Hospital of Nantes, France

⁷  Accident Insurance and Prevention in the Health and Welfare Services, Germany

author email corresponding author email

Journal of Occupational Medicine and Toxicology 2009, 4:30doi:10.1186/1745-6673-4-30

Published:	30 November 2009

Abstract

Introduction

Using French cut-offs for the Tuberculin Skin Test (TST), results of the TST were compared with the results of an Interferon-γ 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.

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.