Analyses of two decades of community-onset pneumonia cases with respiratory viral infections, including respiratory syncytial virus, in adults in a community hospital in Japan.

Information regarding the disease burden of respiratory syncytial virus (RSV) infection among the elderly in Japan is limited. A comprehensive review of the medical records from January 1, 2002, to December 31, 2023, was conducted for adult cases of community-onset pneumonia encountered in routine clinical practice at a community hospital in Shiogama, Japan. The pneumonia case definition employed in this study, for pathogens including major respiratory viruses, required laboratory diagnosis supported by solid virological data, such as virus isolation or rising antibody titers, rather than merely gene detection. The results indicated that, before the emergence of the Coronavirus disease-2019 pandemic in 2020, RSV and influenza virus infections accounted for a substantial proportion (30% each) of the detected respiratory viruses, and RSV persisted as the second most prevalent virus, surpassed only by Severe Acute Respiratory Syndrome Coronavirus-2, even after the pandemic emerged. The mortality rate associated with RSV as a prognostic factor reached 5-10%, depending on the period. The temporal pattern of case emergence from June 2011 to March 2025 suggested that community-acquired RSV infections in children likely precede the occurrence of RSV pneumonia in adults.