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The Value of Interferon Gamma Release Assays for Diagnosis Infection With Mycobacterium Tuberculosis During an Annual Screening of Health Care Workers
To the Editor: In the Diakonessenhuis in Utrecht, the Netherlands, health care workers (HCW) employed at a department with an increased risk for infection with Mycobacterium tuberculosis complex are routinely screened annually with tuberculin skin testing (TST) and an induration of_10 mm is considered positive. Subjects with a positive TST are referred to the Municipal Public Health Department (MPHD) for treatment or follow-up. During the annual screening in 2005 an unexpected high percentage of positive TST results were found. Two hundred seventy-six HCW had been invited for screening of tuberculosis (TB) infection with TST. Of 246 HCW who received a TST, 198 (80%) returned for reading the TST result. Eight HCW (4%) had a TST induration of 5 to 9 mm of whom two had a negative TST and one had a positive TST in the past. Eleven (5.6%) had a positive TST, of whom six had a negative TST and one had a positive TST in the past (Table 1). The findings caused commotion among the personnel since a significant increase of TB infection among HCW was feared. It became apparent during this episode that personnel of the Safety, Health and Welfare Service performing the TST in this hospital was not optimally trained. This was explained by the dynamic composition of the nursing staff performing the TST which precluded maintaining adequate expertise.
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Our results are comparable with those of Nienhaus et al.3 who proposed to replace TST with IGRA for screening of HCW in low incidence countries. Albeit IGRA are more expensive than TST, this strategy was cost-effective since treatment and follow-up can be greatly reduced.4
In conclusion, the findings of this annual TB screening program show that IGRA provide different and more specific information than that of the TST regarding TB infection. It suggests that both overtreatment of subjects with a positive TST in the absence of recent infection and undertreatment of actually infected BCG vaccinated persons are realistic dangers when treatment policy is based only on TST results. This series shows that IGRA can represent a valuable tool in this setting and we recommend the implementation of IGRA for screening of HCW in low-endemic regions.
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Steven F. T. Thijsen, MD, PhD
Department of Medical Microbiology
Diakonessenhuis
Utrecht, The Netherlands
Saskia V. van Rossum, MSc
Department of Infection Prevention
Hospital and Hygiene
Diakonessenhuis, The Netherlands
Sandra Arend, MD, PhD
Department of Infectious Diseases
Leiden University Medical Center
Leiden, The Netherlands
Ben Koster, MD
Municipal Health Authority (GG&GD)
Department of Tuberculosis Control
Utrecht, The Netherlands
Alexander M. Machiels, MD
Department of Safety, Health and Welfare Service,
Diakonessenhuis
Utrecht, The Netherlands
Ailko W.J. Bossink, MD, PhD
Department of Pulmonology and Tuberculosis
Diakonessenhuis, The Netherlands
Department of Medical Microbiology
Diakonessenhuis
Utrecht, The Netherlands
Saskia V. van Rossum, MSc
Department of Infection Prevention
Hospital and Hygiene
Diakonessenhuis, The Netherlands
Sandra Arend, MD, PhD
Department of Infectious Diseases
Leiden University Medical Center
Leiden, The Netherlands
Ben Koster, MD
Municipal Health Authority (GG&GD)
Department of Tuberculosis Control
Utrecht, The Netherlands
Alexander M. Machiels, MD
Department of Safety, Health and Welfare Service,
Diakonessenhuis
Utrecht, The Netherlands
Ailko W.J. Bossink, MD, PhD
Department of Pulmonology and Tuberculosis
Diakonessenhuis, The Netherlands
