Prognostic significance of pleural fluid microbiological positivity in pleural infection: a bicentric 10-year retrospective observational study.

Background: Despite its heterogeneity, there is currently limited data in pleural infection phenotyping. Using pleural fluid characteristics, pleural infection can be classified into microbiological-positive pleural infection (MPPI) and microbiological-negative pleural infection (MNPI). This study aimed to evaluate the prognostic significance of microbiological positivity in pleural infection, and to evaluate the performance of RAPID (renal, age, purulence, infection source, dietary factor) score in these subgroups.
Methods: Consecutive patients hospitalized for pleural infection over a 10-year period in two acute-care hospitals in Hong Kong were evaluated. According to the pleural fluid characteristics, they were classified into MPPI and MNPI, respectively. Survival was evaluated using multivariate Cox regression analysis. Performance of RAPID score to predict mortality at 3-month and 1-year was evaluated using C-statistics.
Results: In total, 381 patients with pleural infection were included. They were classified into MPPI (n = 169) and MNPI (n = 212), respectively. The MPPI group had more elderly home residence and use of large-bore chest tube, and higher Charlson comorbidity index and RAPID score, compared to the MNPI group. Length-of-stay, the need of surgery and intensive care were similar between the two groups. MPPI was associated with significantly increased risk of mortality (adjusted hazard ratio [aHR] 1.46, 95% CI 1.08-1.98). Three-month mortality was significantly higher in MPPI compared to MNPI (24.9% vs. 10.4%, p < 0.001; adjusted odd ratio 2.05, 95% CI 1.11-3.80). The trend continued at 1, 3, 5 and 7 years. RAPID score predicted 3-month and 1-year mortality in both groups (C-statistics, MPPI 0.71, 0.75; MNPI 0.84, 0.81). In the MPPI group, presence of Staphylococcus aureus (aHR 2.26, 95% CI 1.43-3.57) and Gram-negative organisms other than Enterobacteriaceae (aHR 2.00, 95% CI 1.10-3.61) were associated with worse survival, while presence of Streptococcus anginosus group was associated better survival (aHR 0.50, 95% CI 0.32-0.78), when compared to their absence.
Conclusions: Pleural fluid microbiological positivity is independently associated with increased mortality in patients with pleural infections. This finding should complement the RAPID score in risk stratification and inform future research aimed at improving outcomes in this patient population.
Competing Interests: Declarations. Ethical approval: The study was approved by the Institutional Review Board of the Hospital Authority Hong Kong East Cluster (HKECREC-2021-084). Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.
(© 2025. The Author(s).)