Clinical Outcomes Among Older Adults Hospitalized with Respiratory Syncytial Virus and Influenza Infection: A Retrospective Analysis

Abstract Introduction Respiratory syncytial virus (RSV) is a major cause of morbidity and mortality among older adults. Limited information is available in Israel regarding RSV outcomes, particularly compared to influenza, to guide strategies for RSV vaccination. This study aimed to characterize RSV infection and predictors of clinical outcomes among hospitalized adults aged ≥ 60 years in Israel between 2016 and 2023, and to compare disease severity and outcomes with those of seasonal influenza hospitalizations. Methods A retrospective analysis was conducted of hospitalized adults aged ≥ 60 years with positive RSV or influenza confirmed via standard-of-care RT-PCR between 2016 and 2023. The primary outcome was a composite of intensive care unit (ICU) admission, mechanical ventilation, vasopressor support, or 30-day mortality. Cardiovascular complications were recorded. An inverse probability treatment weighting (IPTW) was used to adjust for potential confounding. Weighted and unweighted relative risks (RRs) were estimated to compare clinical outcomes between RSV and influenza. Results Overall, 817 RSV-positive and 2113 influenza-positive patients were included. Among patients with RSV, 30-day and 90-day mortality rates were 11.9% and 18.8% respectively; ICU admission was required for 10.6%, mechanical ventilation for 6.4%, and vasopressor support for 6.5%. Tachyarrhythmia was documented in 17.7% and ischemia in 9.9%. Predictors of the composite primary outcome included chronic pulmonary disease, lower respiratory tract infection, hypothermia, elevated pulse, lower blood pressure and increased creatinine. In IPTW-adjusted analyses, RSV infection had a trend for increased risk for the composite primary outcome (RR 1.03, 95% confidence interval [CI] 1.00, 1.06) and 90-day mortality (RR 1.02, 95% CI 0.99, 1.05) compared with influenza. Conclusions Among hospitalized older adults, RSV infection carries considerable morbidity and mortality and may have a higher risk for poor clinical outcomes compared with influenza. These findings support the prioritization of RSV vaccination programs among older adults.