It is traditionally considered that someone with a positive tuberculin skin test (TST) (and/or positive result in Cell Interferon-Gamma Release Assay (TIGRA), depending on the different countries' guidelines) is infected but not ill when the absence of lesions is demonstrated in a thorax X-Ray assay. Even though, the experiences described in literature using cows and pigs as animal models for the study of LTBI demonstrate the presence of this kind of lesion in the animals, even too small to be detected by X-Ray assay, which would suggest they also could happen in human LTBI. Nowadays, the High Resolution Scanners (HR TC) offer the possibility of detecting any lesion approximately 1 mm in diameter, so the investigators plan to use this technique to screen people already infected by M. tuberculosis (but not ill, following the Diagnosis Standard Guidelines).
Additional pathological analysis of resected and post-mortem tissues will provide lesion-based profiles of humans infected with tuberculosis.
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||June 2012 (Final data collection date for primary outcome measure)
It is traditionally considered that the development of LTBI is due to the M. tuberculosis ability to develop a dormancy state within well-structured lesions (granulomas), which can remain in the lung of the host even for life. The investigators have developed a new original hypothesis based on scientific evidence that takes into account the idea that a lesion cannot be held forever, because the host tends to remove any lesion in order to rebuild the original parenchyma, in a healing process. Even if M. tuberculosis can remain in a dormant/non-replicating state for a long period, this is an important but not sufficient factor to explain the LTBI. The Dynamic Hypothesis tries to explain the existence of LTBI in spite of the healing process that could remove it by a constant reinfection of the host's tissue.