AUTHOR=Dreesman Alexandra , Dirix Violette , Smits Kaat , Corbière Véronique , Van Praet Anne , Debulpaep Sara , De Schutter Iris , Felderhof Mariet-Karlijn , Malfroot Anne , Singh Mahavir , Locht Camille , Mouchet Françoise , Mascart Françoise 

TITLE=Identification of Mycobacterium tuberculosis Infection in Infants and Children With Partial Discrimination Between Active Disease and Asymptomatic Infection

JOURNAL=Frontiers in Pediatrics

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/pediatrics/articles/10.3389/fped.2019.00311

DOI=10.3389/fped.2019.00311

ISSN=2296-2360

ABSTRACT=<p><bold>Background:</bold> Improved diagnostic tests are needed for the early identification of <italic>Mycobacterium tuberculosis-</italic>infected young children exposed to an active TB (aTB) index case. We aimed to compare the diagnostic accuracy of new blood-based tests to that of the tuberculin skin test (TST) for the identification of all infected children and for a potential differentiation between aTB and latent TB infection (LTBI).</p><p><bold>Methods:</bold> 144 children exposed to a patient with aTB were included, and those who met all inclusion criteria (130/144) were classified in three groups based on results from classical investigations: non-infected (NI: <italic>n</italic> = 69, 53%, median age 10 months), LTBI (<italic>n</italic> = 28, 22%, median age 96 months), aTB disease (<italic>n</italic> = 33, 25%, median age 24 months). The first whole blood assay consisted of a 7-days <italic>in vitro</italic> stimulation of blood with four different mycobacterial antigens (40 μl/condition), followed by flow cytometric measurement of the proportions of blast cells appearing among lymphocytes as a result of their specific activation. Thresholds of positivity were determined by Receiver Operating Characteristic (ROC) curve analysis (results of NI children vs. children with LTBI/aTB) in order to identify infected children in a first stage. Other cut-offs were determined to discriminate subgroups of infected children in a second step (results from children with aTB/LTBI). Analysis of blood monocytes and dendritic cell subsets was performed on 100 μl of blood for 25 of these children as a second test in a pilot study.</p><p><bold>Results:</bold> Combining the results of the blast-induced CD3<sup>+</sup> T lymphocytes by Heparin-Binding Haemagglutinin and by Culture Filtrate Protein-10 identified all but one infected children (sensitivity 98.2% and specificity 86.9%, compared to 93.4 and 100% for the TST). Further identification among infected children of those with aTB was best achieved by the results of blast-induced CD8<sup>+</sup> T lymphocytes by purified protein derivative (sensitivity for localized aTB: 61.9%, specificity 96.3%), whereas high proportions of blood type 2 myeloid dendritic cells (mDC) were a hallmark of LTBI.</p><p><bold>Conclusions:</bold> New blood-based tests requiring a very small volume allow the accurate identification of <italic>M. tuberculosis</italic>-infected young children among exposed children and are promising to guide the clinical classification of children with aTB or LTBI.</p>