Research
Evaluation of the tuberculin skin test and the interferon-γ release assay for TB screening in French healthcare workers
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* Corresponding author: Dominique Tripodi Dominique.Tripodi@chu-nantes.fr
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
Journal of Occupational Medicine and Toxicology 2009, 4:30 doi:10.1186/1745-6673-4-30
Published: 30 November 2009Abstract
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.