Pleural Aerobic Culture Status, Clinical Phenotypes, and In-Hospital Outcomes in Adult Pleural Infection: A Retro-Spective Cohort Study

Background and Objectives: Pleural infection is heterogeneous, and the clinical meaning of a positive pleural culture remains uncertain. We compared adults with positive and negative aerobic pleural-fluid cultures and examined associations with major in-hospital events. Materials and Methods: This retrospective, single-center, case-ascertained cohort included adults hospitalized with bacterial pleural infection in Western Romania during 2017–2025. The primary analytic cohort was restricted to patients whose first clinically relevant pleural specimen had an interpretable aerobic culture. Pleural fluid (PF)-positive and PF-negative status was defined exclusively by that result; unperformed tests and operative specimens were not used for classification. The composite outcome comprised in-hospital death, intensive-care unit (ICU) admission/transfer, or thoracic surgery/surgical transfer. Prespecified covariates were entered simultaneously in logistic regression. Results: Of 317 included patients, 276 had an interpretable aerobic pleural culture: 127 (46.0%) were PF-positive and 149 (54.0%) were PF-negative. PF-positive patients were more often institutionalized, had chronic kidney disease, nosocomial infection, frank empyema, and lower pleural-fluid pH and glucose. Streptococci predominated in community-acquired infection, whereas Gram-negative organisms and multidrug-resistant phenotypes were more frequent in healthcare-associated/nosocomial episodes. The composite occurred in 60/127 (47.2%) PF-positive and 51/149 (34.2%) PF-negative patients (OR 1.72, 95% CI 1.06–2.80). The adjusted PF-positive estimate remained imprecise (aOR 1.60, 95% CI 0.94–2.74; p = 0.084), whereas healthcare-associated/nosocomial acquisition was associated with the composite (aOR 1.76, 95% CI 1.03–3.00; p = 0.038). In a sensitivity analysis restricted to 249 patients whose pleural sampling preceded all recorded outcome components, the adjusted association remained imprecise (aOR 1.54, 95% CI 0.86–2.76). Conclusions: A positive aerobic pleural culture identified a distinct high-risk phenotype and influenced antimicrobial management, but its independent association with the heterogeneous in-hospital composite remained uncertain. Acquisition setting and local resistance ecology should guide empirical therapy, and outcome timing should be reported explicitly in future studies.