Impact of emphysema on sputum culture conversion in male patients with pulmonary tuberculosis: a retrospective analysis

Abstract

Background Although cigarette smoking may have a negative impact on the clinical outcome of pulmonary tuberculosis (PTB), few studies have investigated the impact of smoking-associated lung diseases. Emphysema is a major pathological finding of smoking-related lung damage. We aimed to clarify the effect of emphysema on sputum culture conversion rate for Mycobacterium tuberculosis (MTB). Methods We retrospectively studied 79 male patients with PTB confirmed by acid-fast bacillus smear and culture at Jikei University Daisan Hospital between January 2015 and December 2018. We investigated the sputum culture conversion rates for MTB after starting standard anti-TB treatment in patients with or without emphysema. Emphysema was defined as Goddard score ≥1 based on low attenuation area < -950 Hounsfield Unit (HU) using computed tomography (CT). We also evaluated the effect on PTB-related CT findings prior to anti-TB treatment. Results Mycobacterial median time to culture conversion (TCC) in 38 PTB patients with emphysema was 52.0 days [ interquartile range (IQR) 29.0–66.0 days], which was significantly delayed compared with that in 41 patients without emphysema (28.0 days, IQR 14.0–42.0 days) (p<0.001, log-rank test). Multivariate Cox proportional hazards analysis showed that the following were associated with delayed TCC: emphysema [ hazard ratio (HR): 2.43; 95% confidence interval (CI): 1.18–4.97; p=0.015), cavities (HR: 2.15; 95% CI: 1.83–3.89; p=0.012) and baseline time to TB detection within 2 weeks (HR: 2.95; 95% CI: 1.64–5.31; p<0.0001). Cavities and consolidation were more often identified by CT in PTB patients with than without emphysema (71.05% vs 43.90%; p=0.015 and 84.21% vs 60.98%; p=0.021, respectively). Conclusions This study suggests that emphysema poses an increased risk of delayed TCC in PTB. Emphysema detection by CT might be a useful method for prediction of the duration of PTB treatment required for sputum negative conversion.