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Background: Although respiratory tract infection is one of the most important factors triggering acute exacerbation of chronic obstructive pulmonary disease (AE-COPD), limited data are available to suggest an epidemiologic pattern of microbiology in South Korea.Methods: A multicenter observational study was conducted between January 2015 and December 2018 across 28 hospitals in South Korea. Adult patients with moderate-to-severe acute exacerbations of COPD were eligible to participate in the present study. The participants underwent all conventional tests to identify etiology of microbial pathogenesis. The primary outcome was the percentage of different microbiological pathogens causing AE-COPD. A comparative microbiological analysis of the patients with overlapping asthma–COPD (ACO) and pure COPD was performed.Results: We included 1,186 patients with AE-COPD. Patients with pure COPD constituted 87.9% and those with ACO accounted for 12.1%. Nearly half of the patients used an inhaled corticosteroid-containing regimen and one-fifth used systemic corticosteroids. Respiratory pathogens were found in 55.3% of all such patients. Bacteria and viruses were detected in 33% and 33.2%, respectively. Bacterial and viral coinfections were found in 10.9%. The most frequently detected bacteria were Pseudomonas aeruginosa (9.8%), and the most frequently detected virus was influenza A (10.4%). Multiple bacterial infections were more likely to appear in ACO than in pure COPD (8.3% vs. 3.6%, p=0.016).Conclusion: Distinct microbiological patterns were identified in patients with moderate-to-severe AE-COPD in South Korea. These findings may improve evidence-based management of patients with AE-COPD and represent the basis for further studies investigating infectious pathogens in patients with COPD.

Background Although organizing pneumonia (OP) responds well to corticosteroid therapy, relapse is common during dose reduction or follow-up. Predictors of relapse in OP patients remain to be established. The aim of the present study was to identify factors related to relapse in OP patients. Methods This study was retrospectively performed in a tertiary referral center. Of 66 OP patients who were improved with or without treatment, 20 (30%) experienced relapse. The clinical and radiologic parameters in the relapse patient group (n=20) were compared to that in the non-relapse group (n=46). Results Multivariate analysis demonstrated that percent predicted forced vital capacity (FVC), PaO2/FiO2, and serum protein level were significant predictors of relapse in OP patients (odds ratio [OR], 0.82; 95% confidence interval [CI], 0.70-0.97; p=0.018; OR, 1.02; 95% CI, 1.00-1.04; p=0.042; and OR, 0.06; 95% CI, 0.01-0.87; p=0.039, respectively). Conclusion This study shows that FVC, PaO2/FiO2 and serum protein level at presentation can significantly predict relapse in OP patients.

Multicentric Castleman's disease (CD) is a rare atypical lymphoproliferative disorder, which is characterized by various systemic manifestations. Some patients with multicentric CD may have concomitant lung parenchymal lesions, for which lymphoid interstitial pneumonia (LIP) is known to be the most common pathologic finding. Follicular bronchiolitis and LIP are considered to be on the same spectrum of the disease. We describe a case of multicentric CD with pulmonary involvement, which was pathologically proven as follicular bronchiolitis.

Background Viridans streptococci (VS) are a large group of streptococcal bacteria that are causative agents of community-acquired respiratory tract infection. However, data regarding their clinical characteristics are limited. The purpose of the present study was to investigate the clinical and radiologic features of community-acquired pneumonia (CAP) with or without parapneumonic effusion caused by VS. Methods Of 455 consecutive CAP patients with or without parapneumonic effusion, VS were isolated from the blood or pleural fluid in 27 (VS group, 5.9%) patients. Streptococcus pneumoniae was identified as a single etiologic agent in 70 (control group) patients. We compared various clinical parameters between the VS group and the control group. Results In univariate analysis, the VS group was characterized by more frequent complicated parapneumonic effusion or empyema and bed-ridden status, lower incidences of productive cough, elevated procalcitonin (>0.5 ng/mL), lower age-adjusted Charlson comorbidity index score, and more frequent ground glass opacity (GGO) or consolidation on computed tomography (CT) scans. Multivariate analysis demonstrated that complicated parapneumonic effusion or empyema, productive cough, bed-ridden status, and GGO or consolidation on CT scans were independent predictors of community-acquired respiratory tract infection caused by VS. Conclusion CAP caused by VS commonly presents as complicated parapneumonic effusion or empyema. It is characterized by less frequent productive cough, more frequent bed-ridden status, and less common CT pulmonary parenchymal lesions. However, its treatment outcome and clinical course are similar to those of pneumococcal pneumonia.