Polymicrobial etiology as a prognostic factor for empyema in addition to the renal, age, purulence, infection source, and dietary factors score.

Background: Empyema is an important and serious disease with high morbidity and mortality worldwide. However, the bacteriology and prognostic factors of empyema remain poorly understood, and data on the relationships among these parameters are scant.

Methods: We retrospectively analyzed a prospectively collected database of patients with empyema admitted to Kurashiki Central Hospital, Japan, between May 2007 and September 2015. Only patients who had positive results on pleural fluid bacterial culture were included. We collected patient characteristics, bacteriology findings, treatments, and outcomes, and we assessed the prognostic factors for in-hospital mortality.

Results: We included 71 patients in this study. The most commonly isolated bacteria were members of the Streptococcus anginosus group (37%), followed by anaerobes (30%). In-hospital mortality was 11%. On multivariate analysis, polymicrobial empyema (odds ratio [OR], 8.25; 95% confidence interval [CI], 1.08-62.90) and RAPID (renal, age, purulence, infection source, and dietary factors) score (OR, 6.89; 95% CI, 1.73-27.40) were significant risk factors for in-hospital mortality. The most common etiology of polymicrobial empyema was a combination of the members of the S. anginosus group and anaerobes, but no relationship was observed between the combination of microorganisms and outcomes. Although no significant difference was observed in treatment between the survivor and non-survivor groups, all patients who underwent surgery survived.

Conclusions: Members of the S. anginosus group and anaerobes were frequent pathogens in empyema, and polymicrobial etiology was independently associated with mortality in addition to the RAPID score. Surgery may be one option for preventing mortality.