Abstract
BackgroundTuberculosis (TB) still is a major worldwide health problem, with 10.4 million new cases in 2016. Only 5–15% of people infected with M. tuberculosis develop TB disease while others remain latently infected (LTBI) during their lifetime. Thus, the absence of tests able to distinguish between latent infection and active tuberculosis is one of the major limits of currently available diagnostic tools.MethodsA total of 215 patients were included in the study as active TB cases (n = 73), LTBI subjects (n = 88) and healthy persons (n = 54). Peripheral blood mononuclear cells (PBMCs) were isolated from each patient and the LIOSpot® TB anti-human IL-2 ELISpot assay was performed to test their proliferative response to M. tuberculosis antigens ESAT-6, CFP-10 and Ala-DH. Statistical analysis was performed to define the sensitivity and the specificity of the LIOSpot® TB kit for each antigen used and to set the best cut off value that enables discrimination between subjects with active TB or latent TB infection.ResultsComparing the LIOSpot® TB results for each tested antigen between uninfected and infected subjects and between people with latent infection and active TB disease, the differences were significant for each antigen (p< 0.0001) but the ROC analysis demonstrated a high accuracy for the Ala-DH test only, with a cut off value of 12.5 SFC per million PBMCs and the Ala-DH ROC curve conferred a 96% sensitivity and 100% specificity to the test. For the ESAT-6 antigen, with a best cut off value of 71.25 SFC per million PBMCs, a sensitivity of 86% and specificity of 36% was obtained. Finally, the best cut off value for CFP-10 was 231.25 SFC per million PBMCs, with a sensitivity of 80% and a specificity of 54%. Thus, as for IGRA assays such as Quantiferon and T-Spot TB tests, ESAT-6 and CFP-10 are unable to distinguish LTBI from active TB when IL-2 is measured. On the contrary, the IL-2 production induced by Ala-DH, measured by LIOSpot® TB kit, shows high sensitivity and specificity for active TB disease.ConclusionsThis study demonstrates that the LIOSpot® TB test is a highly useful diagnostic tool to discriminate between latent TB infection and active tuberculosis in adults patients.
Highlights
Tuberculosis (TB) still is a major health problem worldwide
Comparing the LIOSpot® TB results for each tested antigen between uninfected and infected subjects and between people with latent infection and active TB disease, the differences were significant for each antigen (p< 0.0001) but the ROC analysis demonstrated a high accuracy for the alanine dehydrogenase (Ala-DH) test only, with a cut off value of 12.5 SFC per million Peripheral blood mononuclear cells (PBMCs) and the Ala-DH ROC curve conferred a 96% sensitivity and 100% specificity to the test
This study demonstrates that the LIOSpot® TB test is a highly useful diagnostic tool to discriminate between latent TB infection and active tuberculosis in adults patients
Summary
Tuberculosis (TB) still is a major health problem worldwide. In 2016, there were 10.4 million new estimated cases worldwide. Incident TB cases reflect a little percentage of the global infection burden: in the great majority of immunocompetent persons, infection with Mycobacterium tuberculosis (MTB) is initially contained by the host immune system, resulting in a latent TB infection (LTBI) which is characterized by the presence of immune responses to MTB in the absence of clinical, radiological and microbiological evidences [2]; 5–15% of the infected people develop TB disease during their lifetime, being a reservoir of new active TB cases [1, 3, 4]. Tuberculosis (TB) still is a major worldwide health problem, with 10.4 million new cases in 2016. The absence of tests able to distinguish between latent infection and active tuberculosis is one of the major limits of currently available diagnostic tools
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