Interferon-gamma release assay versus tuberculin test in diagnosis of latent tuberculosis infection among healthcare workers, Sana'a city Yemen

Abstract

Background: Latent tuberculosis infection (LTBI) is the presence of Mycobacterium tuberculosis in the body without evidence of tuberculosis (TB) disease. Healthcare workers (HCWs) are at occupational risk of contracting & transmitting TB. Therefore, identifying of persons with LTBI is an essential TB prevention & control strategy. The aim of this study was to evaluate the performance of interferon-gamma release assay (IGRA) in diagnosis of LTBI among HCWs, in comparison to tuberculin skin test (TST); as well as identifying risk factors fortest positivity.Methods: A cross-sectional study was conducted in 2015 on 90 HCWs tested with TST and IGRA. All Participants were subjected to a questionnaire to assess their risk factors. Differences between categorical variables were analyzed by X2. Kappa coefficient used to detect the agreement between TST and IGRA. Also, accuracy of both tests was calculated.  Results: Of the 90 HCWs; 54.4% were females and 45.6% were males with an age ranged between 20-60 years. The participants were classified as 38.9% nurses, 34.4% physicians, 16.7% technicians and 10% were administrators. The highest prevalence of LTBI was found in female 14.3% & 28.6% by TST and IGRA, respectively. In general, the positivity by both tests increased with increasing age. 27.8% of HCWs were Bacille Calmette-Guérin (BCG) vaccinated and most of the positivity occurs among vaccinated HCWs. The crude prevalence for LTBI was 12.2% by TST and 20% by IGRA; overall agreement between TST and IGRA results was poor (k= 0.39).Conclusion: Most HCWs with LTBI were females, nurses, older age, BCG vaccinated and in a group of profession of close contact with TB patients'. The higher positivity was found by IGRA than by TST with poor agreement between them.Superior specificity was observed with IGRA; whereas TST had a higher sensitivity.