Clinical profiles of subclinical disease among pulmonary tuberculosis patients: a prospective cohort study in South Korea

Abstract Background: Subclinical tuberculosis (TB) is a potential target for public health intervention because its early identification may reduce TB transmission. Here, we have described clinical and laboratory findings of subclinical disease among pulmonary TB patients. Methods: In this prospective cohort study, we enrolled adult patients with pulmonary TB between 2016 and 2018. Subclinical TB was defined as the presence of radiographic or microbiologic test results consistent with TB without clinical symptoms. We implemented two-stage symptom assessment using a predefined TB symptom checklist. Demographic, clinical, and laboratory data were compared between subclinical and active disease using the multivariate binary logistic regression analysis. We evaluated treatment outcomes in the drug-susceptible cohort. Results: Among 420 enrolled patients, 81 (19.3%) had subclinical TB. Multivariate analysis showed that age <65 years was the only significant variable associated with subclinical disease. Subclinical disease had a significantly lower proportion of acid-fast bacilli smear and culture positivity and multiple lobe involvement compared to active disease. Among 319 patients with treatment success in the drug-susceptible cohort, six (1.9%) recurrent cases were identified, and all were active disease. Patients with subclinical disease had a higher proportion of favorable outcomes; however, its odds ratio was insignificant. Conclusions: Nearly one-fifth of tuberculosis cases were subclinical under the universal health coverage in South Korea. Despite its milder clinical presentation, the treatment outcomes of subclinical TB were not significantly different from that of active disease.