BackgroundLithuania is a country with a high incidence of tuberculosis (TB), despite a high coverage with bacille Calmette-Guerin (BCG) vaccination. Until now the only method used to detect latent TB infection was the tuberculin skin test (TST). However, TST may have a cross reactivity to the BCG vaccine and to environmental mycobacteria. The aim of this study was to conduct assessments of the diagnostic accuracy of the T-cell based test (T SPOT TB) for TB in children who had previously been BCG vaccinated and compare these with the results of the TST.MethodsBetween January 2005 and February 2007, children with bacteriologically confirmed TB, children having contacts with a case of infectious pulmonary TB and children without any known risk for TB were tested with both the TST and T SPOT TB.ResultsThe TST and T SPOT TB tests were positive for all patients in the „culture-confirmed TB“ group. Whereas, in the „high risk for TB“ group, the TST was positive for 60%, but the T SPOT TB test, only for 17.8%. Meanwhile the results for the „low risk for TB“ group were 65.4% and 9.6%, respectively. A correlation between the TST and T SPOT TB was obtained in the "culture-confirmed TB" group where the TST ≥15 mm (r = 0.35, p < 0.001).ConclusionThe T-cell based method is more objective than the TST for identifying latent TB infection in children who had been previously BCG vaccinated. This method could be useful in countries like Lithuania where there is a high incidence of TB despite a high coverage with BCG vaccination. It may also help to avoid unnecessary chemoprophylaxis when TST reactions are false-positive.
Tuberculosis is one of the biggest global health problems. One-third of the world’s population (2 billion) is latently infected with tuberculosis. The tuberculin skin test is commonly used to diagnose tuberculosis infection. This test has poor specificity and sensitivity, cross-reactivity with bacille Calmette-Guérin vaccination and many environmental mycobacteria, and poor sensitivity (only 75–90% in active tuberculosis). Mycobacterium tuberculosis activates a strong T cell-mediated immune response. That is why, a better marker for tuberculosis infection could be the presence of mycobacteria specific interferon-y-secreting T cells. These cells can be identified in blood or any other sample, which contains T cells. The test specificity is 99.9% (in low-risk control groups), and the sensitivity is 97.2% (in subjects with culture-confirmed active disease). New in vitro diagnostic test of tuberculosis, based on tuberculosis-induced immunological mechanisms, seems to be more specific and useful as previous methods.
The T SPOT TB showed greater accuracy in diagnosing TB than TST did. Positive T SPOT TB result but not the TST was more common in patients with diagnosed TB.
Tuberkuliozė – viena grėsmingiausių, plačiai pasaulyje paplitusių lėtinių infekcinių ligų, lemianti didelį mirtingumą. Dažniausiai taikomas metodas latentinei tuberkuliozės infekcijai nustatyti yra įodinis tuberkulino mėginys, kurio jautrumas nepakankamas, ypač BCG vakcina skiepytųjų populiacijoje. Siekiant efektyvesnės tuberkuliozės infekcijos diagnostikos, sukurti nauji in vitro diagnostiniai metodai, kurie pagrįsti M. tuberculosis sukelto imuninio atsako ypatumų vertinimu, t. y. stimuliuotų T limfocitų išskiriamo gama interferono (IFN-γ) nustatymu.
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