Outcomes related to Bacterial Co-infection and Antibiotic use in Adults Hospitalized with Respiratory Syncytial Virus compared to Influenza

Background Adults hospitalized with respiratory syncytial virus (RSV) face mortality risks comparable to or higher than those with Influenza A or B. However, studies on the impact of bacterial co-infections on mortality are inconsistent. Methods This multicenter cohort study included adults hospitalized with RSV, Influenza A, or B over three years at two tertiary care hospitals. Microbiological testing, bacterial co-infections, antibiotic use, and their association with clinical outcomes were analyzed using adjusted linear and logistic regression models. Results Of 986 patients, 352 (36%) had RSV, 347 (35%) influenza A, and 287 (29%) influenza B. The median age was 74 years, 54% were women, and 76% had at least one comorbidity. Overall, 32% had pneumonia. The prevalence of bacterial co-infections was comparable across patients with RSV (23%), influenza A (25%), and B (28%). Among patients without bacterial co-infection, antibiotic use within 48 hours remained common across all virus groups (77%, 71%, and 75%, respectively). In adjusted analyses, bacterial co-infection in patients with RSV was not associated with mortality at 14, 30, or 90 days, high-flow oxygen therapy, mechanical ventilation, or length of stay (LOS). Early antibiotic treatment was associated with prolonged LOS but not improved survival. Conclusion Bacterial co-infections were identified in approximately one-quarter of patients with RSV, influenza A, and B. Among patients with RSV, bacterial co-infection was not associated with adverse clinical outcomes, and early antibiotic treatment did not appear to improve clinical outcomes.