Comparison of clinical characteristics and outcomes between patients with complicated pleural infection caused by Streptococcus anginosus group and Klebsiella pneumoniae.

Objectives: Complicated pleural infections present significant challenges. Predominant causative microorganisms include the Streptococcus anginosus group (SAG) and Klebsiella pneumoniae (KP). However, limited data are available on the risk factors and outcomes associated with SAG-related pleural infection compared to KP-related pleural infection. Methods: This retrospective study was conducted in patients who underwent pleural drainage due to complicated pleural infection at Kyungpook National University Hospital in South Korea between January 2011 and December 2023. Clinical characteristics, drug resistance profiles, and outcomes were compared between patients with SAG-related and KP-related pleural infections. Results: A total of 432 patients were assessed. Among them, 161 (37 %) had positive pleural fluid cultures, with SAG (n=68, 42 %) and KP (n=34, 21 %) being the predominant pathogens. Thus, 102 patients with complicated pleural infection caused by SAG or KP were analyzed. SAG cases were associated with higher rates of chronic neurologic disease, lower rates of diabetes mellitus, prolonged symptom duration, elevated white blood cell counts, and positive gram stains on pleural fluid compared to KP cases. There were no significant differences observed between the two groups regarding radiological findings. SAG strains showed resistance rates exceeding 20 % to penicillin, erythromycin, tetracycline, and clindamycin, while remaining largely susceptible to commonly used third-generation cephalosporins, ampicillin, and fluoroquinolones. The in-hospital mortality rates were approximately 10 %, consistent across both groups. Conclusions: SAG-related pleural infections showed distinct clinical features, including more frequent chronic neurologic disease, but in-hospital mortality was comparable to that of KP-related infections.