Evolution of Interferon-gamma Release Assay Results and Submillisievert Chest CT Findings among Close Contacts of Active Pulmonary Tuberculosis Patients.

Background Latent tuberculosis (TB) infection among TB contacts is diagnosed using plain chest radiography and interferon-gamma release assays (IGRAs). However, plain chest radiographs often miss active TB, and the results of IGRA could fluctuate over time. The aim of this study was to elucidate changes in the results of serial IGRAs and in the findings of serial submillisievert chest computed tomography (CT) scans among the close contacts of active pulmonary TB patients. Methods Patients aged 20 years or older with active pulmonary TB and their close contacts were invited to participate in this study. Two types of IGRA [QuantiFERON-TB Gold In-Tube assay (QFT-GIT) and the T-SPOT.TB test (T-SPOT)] and submillisievert chest CT scanning were performed at baseline and at 3 and 12 months after enrollment. Results In total, 19 close contacts participated in this study. One was diagnosed with active pulmonary TB and was excluded from further analysis. At baseline, 4 (22.2%) of 18 contacts showed positive results for both QFT-GIT and T-SPOT; there were no discordant results. During follow-up, transient and permanent positive or negative conversions and discordant results between the two types of IGRAs were observed in some patients. Among the 17 contacts who underwent submillisievert chest CT scanning, calcified nodules were identified in 7 (41.2%), noncalcified nodules in 14 (82.4%), and bronchiectasis in 4 (23.5%). Some nodules disappeared over time. Conclusions The results of QFT-GIT and T-SPOT assays and CT images may change during 1 year of observation of close contacts of active TB patients.