Predictors and Clinical Impact of Positive Blood Cultures in Emergency Department Patients with Suspected Infection

Background and Objectives: Blood cultures are routinely obtained in emergency department (ED) patients with suspected infection; however, their real clinical impact on patient outcomes remains debated. Although current sepsis guidelines recommend obtaining blood cultures before antimicrobial therapy, the diagnostic yield is relatively low, and it remains unclear whether early microbiological results meaningfully influence prognosis. To evaluate the predictors and clinical impact of positive blood cultures in ED patients with suspected infection and to assess whether microbiological results that modify empiric antimicrobial therapy are associated with improved survival. Materials and Methods: We conducted a retrospective cohort study of adult patients presenting to a tertiary-care ED with suspected infection between 2018 and 2024 who underwent blood culture sampling within the first six hours of ED stay. Blood culture results were classified as negative, positive non-actionable, or positive actionable depending on whether they led to modification of empiric antimicrobial therapy. The primary outcome was in-hospital mortality. Survival analysis was performed using Kaplan–Meier curves and multivariable Cox regression with a 72 h landmark approach to reduce immortal time bias. Results: The study included 13,591 patients with suspected infection who underwent blood culture testing. Blood cultures were negative in 11,475 patients, positive non-actionable in 1082 patients, and positive actionable in 1034 patients. Overall in-hospital mortality was approximately 14%. Kaplan–Meier analysis showed significant differences in survival across blood culture groups (log-rank p < 0.001), with lower crude survival among patients with actionable positive cultures. However, after adjustment for demographic characteristics, comorbidity burden, illness severity, and laboratory markers in multivariable Cox regression models, the presence of an actionable blood culture result was not associated with improved prognosis compared with negative or non-actionable cultures. Conclusions: In ED patients with suspected infection, actionable positive blood cultures were associated with higher crude mortality; however, after multivariable adjustment, this association was attenuated and did not remain statistically significant. These findings suggest that actionable blood culture results identify patients with greater illness severity and clinical complexity, while their direct patient-level survival benefit remains difficult to demonstrate in observational data. Further prospective studies are needed to clarify whether early blood culture acquisition can truly modify the clinical trajectory of patients with suspected infection.