Characteristics of culture-negative subclinical pulmonary tuberculosis: a single-center observation

Abstract

Background: Little is known about culture-negative subclinical pulmonary tuberculosis (TB), and its diagnosis remains challenging. Therefore, this study aimed to identify the characteristics and the extent of disease associated with culture-negative subclinical pulmonary TB.

Methods: This retrospective cohort study was conducted on immunocompetent individuals with subclinical pulmonary TB at a university hospital in Thailand from January 2014 to December 2019. Subclinical pulmonary TB was diagnosed based on the presence of radiographic abnormalities consistent with TB in the absence of TB symptoms. All subjects demonstrated significant improvement or resolution of radiographic abnormalities following the completion of treatment. At least two negative sputum cultures were needed to fulfill the definition of culture-negative pulmonary TB. Data were analyzed using univariate and multiple logistic regression analyses to determine the characteristics of those with culture-negative subclinical pulmonary TB compared to culture-positive ones.

Results: Out of the 106 individuals identified with subclinical pulmonary TB, 84 met the criteria for inclusion in the analysis. The study found lower radiographic extent and increasing age were key attributes of culture-negative subclinical pulmonary TB. The odds ratios (95% confidence interval) were 7.18 (1.76 to 29.35) and 1.07 (1.01 to 1.13), respectively. They tend to have lower rates of bilateral involvement in both chest x-ray (8.5% vs. 32.0%, p=0.006) and computed tomography (15.4% vs. 42.9%, p=0.035). However, no other specific radiographic findings were identified.

Conclusions: People with culture-negative subclinical pulmonary TB were likely to have less radiographic -severity, reflecting early disease. Nevertheless, no radiographic patterns, except for unilaterality, were related to culture-negative subclinical pulmonary TB.

Figure 1

Flow Diagram of the Study.

Figure 2

A–C) Pre- and post-treatment chest images of a 26-year-old female with culture-positive subclinical pulmonary TB. A) Pre-treatment chest radiograph shows reticulonodular opacities at the right apical lung. B) Axial CT image in lung window performed 1 month after A. reveals multiple centrilobular nodules with tree-in-bud pattern in the apical segment of the right upper lobe. C) Post-treatment chest radiograph (7 months after A.) shows resolution of the abnormalities of the right apical lung.

Figure 3

A–C) Pre- and post-treatment chest images of a 32-year-old female with culture-negative subclinical pulmonary TB. A) Pre-treatment chest radiograph shows patchy nodular opacities at the right middle lung zone. B) Axial CT image in lung window performed on the same date as A. reveals solid pulmonary nodules with adjacent centrilobular and tree-in-bud opacities in the superior segment of the right lower lobe as well as bronchial wall thickening and bronchiectasis. C) Post-treatment chest radiograph (10 months after A.) shows resolution of the abnormalities with minimal residual fibrosis at the right middle lung zone.