Abstract
Tuberculosis is still one of the major global public health threats. Countries with low incidence must focus on exhausting the reservoir of future cases by preventing reactivation. Therefore, it is important to identify and effectively treat those individuals who have latent tuberculosis infection and who may develop active disease. The tuberculin skin test has been the standard for detection of immune response against M. tuberculosis since the beginning of the 20th century. The new millennium has brought advancement in the diagnosis of latent tuberculosis infection. The name of the new blood test is interferon-gamma release assay (IGRA). Croatia is a middle-incidence country with a long decreasing trend and developed tuberculosis control. To reach low incidence and finally eliminate tuberculosis, its tuberculosis programme needs a more aggressive approach that would include intensive contact investigation and treatment of persons with latent tuberculosis infection. This article discusses the current uses of IGRA and its role in tuberculosis control.
Highlights
Teaching Public Health Institute of Split and Dalmatia County and School of Medicine University of Split, Split1, Croatian National Institute of Public Health Zagreb2, Split University Hospital, Department of pulmonary diseases, and School of Medicine University of Split, Split3, Croatia
The first was with purified protein derivative (PPD) as the antigen, which is not longer commercially available; the second was QuantiFERON®-TB Gold (QFT-G), with early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10); and QuantiFERON®-TB Gold In-Tube (QFT-G-IT), with ESAT-6, CFP-10, and TB7.7
Current research has shown that the level of agreement between the interferon-gamma release assay (IGRA) and TST is lower if the tested population received Bacillus Calmette-Guerin (BCG)
Summary
Many studies have reported on IGRA’s performance. They differ in regard to TB incidence, prevalence of infection, patient age, status of the immune system, prevalence of HIV-coinfection, antigens used (older or newer generation), and tuberculin units used during TST. The sensitivity and specificity of IGRAs or TST for LTBI cannot be reliably estimated because there is no gold method for the diagnosis of LTBI. This is why two surrogates for infection are used to estimate sensitivity. Even though more studies have estimated T-SPOT.TB sensitivity than that of QFT, they all show that both tests better correlate with TB exposure than TST and do not depend of BCG vaccination [11, 16, 18, 19]. Pai et al [14] reported that pooled specificity of QFT tests was higher among non BCG-vaccinated individuals (99 %) than among vaccinated (96 %), while pooled specificity of T-SPOT.TB was 93 %. IGRAs have a higher specificity than TST, in BCG-vaccinated population
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