Understanding polymicrobial bloodstream infections: clinical and microbiological insights from a Spanish university...

Evidence on polymicrobial bloodstream infections (PMB) in Spain remains limited. In this study, we aimed to describe its etiology, clinical features and outcomes in adult patients.

A retrospective observational study was conducted at a 350-bed hospital in Terrassa, Barcelona, from 2017 to 2024. Clinical and microbiological data were reviewed. Bivariate analyses and multivariate logistic regression were applied to identify predictors of 30-day mortality.

We identified 115 episodes. Intra-abdominal foci represented 50% of cases. Non-anaerobic Gram-negative bacilli predominated, either alone (31%) or combined with Gram-positive cocci (40%), while anaerobes appeared in 14%. Thirty-day mortality was 30%. In the multivariable analysis, three variables remained independently associated with mortality: baseline prognosis (McCabe-score), acute severity (Pitt bacteremia-score) and adequacy of empirical therapy.

PMB is associated with high mortality. Prognosis is influenced by host vulnerability, infection severity and the initial empirical treatment. Early recognition and adequate empirical therapy are essential to improve outcomes.