Clinical insights into mixed Candida and bacterial bloodstream infections: a retrospective cohort study

Mixed bloodstream infections (BSIs) involving Candida and other bacterial pathogens present significant diagnostic and therapeutic challenges. The incidence of these co-infections has been increasing. However, the limited literature on this topic necessitates a deeper understanding of its epidemiological and clinical characteristics. This retrospective study evaluated adult patients with candidemia across three hospitals in Taiwan between January 2014 and December 2020. Mixed Candida/bacterial BSIs were defined as the concurrent isolation of bacterial species from any set of blood cultures within 1 week of the initial Candida culture. The clinical features and 30-day mortality of mixed Candida/bacterial BSIs were investigated. Among 766 patients with candidemia, 193 (25.2%) had mixed Candida/bacterial BSIs. The 30-day mortality for mixed infections was significantly higher than for monomicrobial candidemia (62.7% vs. 51.7%, P = 0.009). The mortality rates and intervals between Candida and bacterial blood culture isolation had a negative correlation (P = 0.004). In the mixed Candida/bacterial BSI cases, the most common bacteria included coagulase-negative staphylococci, Enterococcus spp., and Klebsiella spp. Co-infection with vancomycin-resistant Enterococcus had a significantly higher mortality rate than mono-candidemia (P = 0.015). Significant predictors of 30-day mortality included high Pitt score, high sequential organ failure assessment (SOFA) score, inappropriate empiric antibiotics, and lack of adherence to the European Confederation of Medical Mycology Quality of Clinical Candidaemia Management (EQUAL) score. In conclusion, mixed Candida/bacterial BSIs are associated with high mortality and severe clinical conditions. Empirical antibiotic strategies and tailored antifungal treatments, aligned with clinical guidelines, have significantly improved patient outcomes.IMPORTANCEMixed bloodstream infections with Candida and bacteria are serious and deadly. This study demonstrated that Candida/bacterial bloodstream infections (BSIs) accounted for 25.2% of all candidemia cases and were associated with significantly higher 30-day mortality compared with monomicrobial candidemia (62.7% vs 51.7%). Patients with mixed BSIs exhibited more severe clinical conditions, a higher rate of inappropriate antibiotic use, and a greater prevalence of multidrug-resistant organisms. The study further demonstrated that adherence to antifungal treatment recommendations (EQUAL Candida score) and timely initiation of appropriate empirical antibiotics were associated with improved survival. These findings fill a critical gap in the literature and provide important insights into the management of mixed Candida/bacterial BSIs, with implications for optimizing diagnostic and therapeutic strategies in clinical practice.