Clinical and Microbial Insights into Polymicrobial Vascular Graft Infections: A Prospective Observational Study

Objectives Vascular graft/endograft infections (VGEI) are difficult-to-treat and associated with high morbidity and mortality. Up to 40% of VGEI are polymicrobial, complicating clinical management. This study investigates microbial interactions and their impact on clinical outcomes. Methods We analyzed patient characteristics and survival in poly- versus monomicrobial infections from the VASGRA cohort, a Swiss prospective observational study. Kaplan-Meier analysis and Cox proportional hazards models were used to assess survival. Furthermore, a subset of patient-derived bacterial strains underwent Quantitative Fitness Analysis (QFA) to quantify changes in fitness in mono- and polymicrobial conditions. Results Among 227 VGEI episodes, 81 (35.7%) were polymicrobial. The overall survival rate was 84.4% at two years and 77.5% at five years, with polymicrobial infections associated with lower survival (logrank ranktest p = 0.004). Multivariable analyses confirmed that polymicrobial infections (adjusted HR = 2.91, 95% CI: 1.56–5.42, p = 0.001), age per 10 years older (adjusted HR = 2.08, 95% CI: 1.28–3.40, p = 0.003), and diabetes mellitus (adjusted HR = 2.12, 95% CI: 1.08–4.13, p = 0.028), were independent risk factors for increased mortality. QFA of five strain pairs revealed diverse interaction patterns among pathogens, ranging from complete inhibition to enhanced growth in co-culture. Conclusion Polymicrobial infections, along with older age and diabetes mellitus, were identified as independent risk factors for increased mortality in VGEI patients. QFA revealed diverse bacterial interactions, highlighting the complexity of polymicrobial environments in VGEI.