Pulmonary Tuberculosis Incidence among Interferon-gamma Release Assays Positive Latent Tuberculosis Infection with Fibrotic Lesions in an Urban Vulnerable Population of Osaka City, Japan, 2015-2021.

Latent tuberculosis infection (LTBI) with fibrotic lesions (FL) can progress to active tuberculosis (TB). Previous studies did not use interferon-gamma release assays (IGRAs) but used tuberculin skin tests for LTBI diagnosis, whose specificity was lower. This study evaluated the incidence of active TB among LTBI with FL who were diagnosed with IGRAs in Nishinari District, Osaka City. In total, 54 men were registered with 68.7 years old of a mean age, ten (18.5%) were homeless, and 36 (66.7%) were welfare recipients. Overall, with the median period of observation of 1,084 days (range: 64-2,907 days), an incidence rate of active TB among LTBI with FL was 1.18 cases per 100 person-years (95% confidence interval: 0.32-4.29). Among 19 (35.2%) who had never been treated with anti-TB therapy, one (5.3%) progressed to active TB, and among 30 (55.6%) who completed the treatment, one (3.3%) progressed to active TB. The others five did not have TB. We revealed the incidence of active TB among LTBI with FL in an urban vulnerable population for the first time, using IGRAs for the diagnosis of LTBI. A higher incidence than that reported in previous studies reinforces the importance of strategies, including chest radiography screening and LTBI treatment.