Routinely Available Prognostic Factors for Adverse Outcomes in Adults with Complicated Parapneumonic Effusion and...

Background: Pleural infection remains associated with substantial morbidity, mortality, and frequent treatment escalation. This systematic review and meta-analysis evaluated routinely available prognostic factors associated with adverse clinical outcomes in adults with pleural infection, including complicated parapneumonic effusion and pleural empyema. Methods: PubMed, Scopus, Web of Science Core Collection, and the Cochrane Library were searched from inception to 6 July 2026. Studies evaluating routinely available clinical, biochemical, microbiological, pleural fluid, radiological, or composite prognostic factors were included. Methodological quality was assessed using the Newcastle-Ottawa Scale (NOS). Comparable data were synthesized using random-effects meta-analysis. Results: Thirty studies involving 8443 participants were included. The evaluated outcomes comprised treatment failure, short-term mortality, need for surgery, intensive care unit admission, recurrence, readmission, and length of hospital stay. Five studies (877 participants) contributed to the RAPID score meta-analysis. High-risk RAPID classification was associated with greater short-term mortality than combined low- and intermediate-risk classification (RR 4.52, 95% CI 2.71-7.55; primary OR 6.09, 95% CI 3.25-11.38; I² = 0% for the OR analysis). In a limited meta-analysis of three studies (1239 participants), each 10-year increase in age was associated with higher odds of short-term mortality (OR 1.54, 95% CI 1.02-2.30; I² = 30.4%); however, mortality was assessed in hospital in two studies and at 90 days in one study. Additional prognostic factors associated with adverse outcomes included comorbidity burden, renal dysfunction, hypoalbuminemia, serial C-reactive protein trajectories, bacteremia, pleural fluid biochemical markers, pleural thickening, loculation, and delayed or ineffective drainage, although heterogeneous reporting precluded further quantitative synthesis. Conclusions: The RAPID score is the most consistently supported routinely available predictor of short-term mortality in adults with pleural infection. Increasing age may also be prognostic, but its pooled estimate is based on only three studies with different mortality windows and should be interpreted cautiously. Future prospective multicenter studies using standardized outcome definitions are needed to validate additional prognostic markers and improve risk-guided clinical decision-making.