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Open Access Highly Accessed Research article

Screening for latent tuberculosis in Norwegian health care workers: high frequency of discordant tuberculin skin test positive and interferon-gamma release assay negative results

Gerd Gran1, Jörg Aßmus2 and Anne Ma Dyrhol-Riise345*

Author Affiliations

1 Department of Pulmonary Medicine, Haukeland University Hospital, Bergen, N-5021, Norway

2 Centre for Clinical Research, Haukeland University Hospital, Bergen, N-5021, Norway

3 Department of Clinical Science, University of Bergen, Bergen, N-5021, Norway

4 Department of Internal Medicine, Section for Infectious Diseases, Haukeland University Hospital, Bergen, N-5021, Norway

5 Present address: Department of Infectious Diseases, Oslo University Hospital, pb 4956 Nydalen, Oslo, 0424, Norway

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BMC Public Health 2013, 13:353  doi:10.1186/1471-2458-13-353

Published: 17 April 2013

Abstract

Background

Tuberculosis (TB) presents globally a significant health problem and health care workers (HCW) are at increased risk of contracting TB infection. There is no diagnostic gold standard for latent TB infection (LTBI), but both blood based interferon-gamma release assays (IGRA) and the tuberculin skin test (TST) are used. According to the national guidelines, HCW who have been exposed for TB should be screened and offered preventive anti-TB chemotherapy, but the role of IGRA in HCW screening is still unclear.

Methods

A total of 387 HCW working in clinical and laboratory departments in three major hospitals in the Western region of Norway with possible exposure to TB were included in a cross-sectional study. The HCW were asked for risk factors for TB and tested with TST and the QuantiFERON®TB Gold In-Tube test (QFT). A logistic regression model analyzed the associations between risk factors for TB and positive QFT or TST.

Results

A total of 13 (3.4%) demonstrated a persistent positive QFT, whereas 214 (55.3%) had a positive TST (≥ 6 mm) and 53 (13.7%) a TST ≥ 15 mm. Only ten (4.7%) of the HCW with a positive TST were QFT positive. Origin from a TB-endemic country was the only risk factor associated with a positive QFT (OR 14.13, 95% CI 1.37 - 145.38, p = 0.026), whereas there was no significant association between risk factors for TB and TST ≥ 15 mm. The five HCW with an initial positive QFT that retested negative all had low interferon-gamma (IFN-γ) responses below 0.70 IU/ml when first tested.

Conclusions

We demonstrate a low prevalence of LTBI in HCW working in hospitals with TB patients in our region. The “IGRA-only” seems like a desirable screening strategy despite its limitations in serial testing, due to the high numbers of discordant TST positive/IGRA negative results in HCW, probably caused by BCG vaccination or boosting due to repetitive TST testing. Thus, guidelines for TB screening in HCW should be updated in order to secure accurate diagnosis of LTBI and offer proper treatment and follow-up.

Keywords:
Tuberculosis; Quantiferon; Interferon-gamma release assay; IGRA; Screening; Health care workers; Low-endemic country, Norway