ANALISI DI UNA NUOVA METODICA DI LABORATORIO PER LO STUDIO DELLA RISPOSTA IMMUNOLOGICA ALL'INFEZIONE LATENTE DA MYCOBACTERIUM TUBERCULOSIS

Identification and treatment of individuals with latent tuberculosis infection (LTBI) is an important component of tuberculosis elimination strategies in low incidence countries. In this context, health care workers (HCWs) represent an important target population for LTBI screening programmes and serial testing is recommended for HCWs. Interferon-gamma release assays (IGRAs) are alternatives to the tuberculin skin test (TST) and have been recommended for serial testing, but data are scarce on the interpretation of repeated IGRAs results. Existing studies, although limited, suggest that conversions, reversions and non-specific variations occur. However, there is no definitive consensus on how to define and interpret IGRA conversions and reversions. At Padua Hospital (Italy) we conducted two different studies. In the first, run during 2006, 1715 HCWs were requested to perform both a TST and a blood sample for QuantiFERON-TB Gold In-Tube (QF-GIT) to compare the effectiveness and qualitative reproducibility of the QF-GIT versus TST for screening HCWs for LTBI. In the second investigation, which lasted three years since 2006 and was recently concluded, 530 HCWs were repeatedly screened (three or more times) for LTBI only with QF-GIT. The occurrence of consistently positive (or negative) results and different QF-GIT variations were thoroughly studied, and the variability and reproducibility of quantitative results evaluated. An analysis of association between consistently positive (or negative) results and personal characteristics was also performed, showing that the probability of being affected by LTBI is positively correlated with gender, age and professional qualification. Based on our results, it emerges that the QF-GIT test is reliable, its results are reproducible over time making it a valuable tool in selected populations, such as the HCWs, in surveillance programs and control of LTBI.