Evaluation of Interferon Gamma Release Assay in the Diagnosis of Active and ‎Latent Tuberculosis among Patients and Contacts ‎

Abstract

Background and study aim: To date, tuberculosis (TB) is a global health emerging disease. Early detection of TB infection is critical to start therapy and stop increasing the prevalence of TB cases. The presence of sensitive, non-invasive, rapid and cheap method for diagnosing active and latent TB is very crucial to control TB transmission‎.The current study aims to compare the results of Ziehl-Neelsen (ZN) and tuberculin skin test (TST or Mantoux) with the QuantiFERON-TB Gold in-tube Test (QFT-GIT) in the diagnosis of active TB and latent infection. Patients and method: The study included 90 participants divided into 45 clinically and microbiologically diagnosed patients with pulmonary tuberculosis (PTB) and 45 close contacts to PTB patients. Both groups examined clinically, and subjected to three diagnostic tests; ZN, Mantoux, and QFT- GIT. Results: The TST was positive in 95.6% and 42.2% of patients and contacts, respectively. Out of the screened TB patients and contacts, the positive QFT-GIT was found among 86.7% and 68.9%, respectively. The total agreement between QFT-GIT and the Mantoux was 71.11%. Positive concordant results (QFT+/TST+) were observed in 86.9%, while negative concordant results (QFT-/TST-) were detected in 37.9% of patients and contacts‎. Conclusion: The evaluation results of the QFT-GIT with ZN and Mantoux showed high sensitivities but relatively low specificities. The specificity of QFT-GIT was improved by modifying the cut off values to higher levels. Latent tuberculosis infection (LTBI) was likely to occur when both QFT-GIT and TST were positive ‎.