Nationwide Epidemiology and Outpatient Healthcare Resource Use of Children with Respiratory Syncytial Virus from 2005 to 2021

Respiratory syncytial virus (RSV) poses a global health challenge, particularly among younger children. While the disease burden in Japan has been preliminarily quantified in short-term or inpatient settings, a comprehensive understanding of outpatient settings at a national level is still lacking. In this retrospective cohort study, we followed 697 802 children until they reached 60 months of age, amounting to 25 680 468 million person-months, using two nationally representative databases from the fiscal years 2005-2021. We analyzed trends in the epidemiology of RSV infections and associated outpatient health resource use. Incidence rates of RSV and associated hospitalizations among infants showed fluctuations of 50-100 cases and 20-30 hospitalizations per 1000 person-years, respectively, during the 2010s. These rates dropped to 8.7 cases and 2.2 hospitalizations per 1000 person-years in 2020, then returned to the same levels in the 2010s. Similar patterns were noted for RSV testing, outpatient visits, healthcare cost, and the proportion of cases hospitalized (case-hospitalization risk). Whereas antibiotic use decreased from 56.4% in 2005 to 27.8% in 2021, palivizumab use increased from 95.2 to 195.9 days of therapy per 1000 person-years. Applying the calculated incidence rates to national data, annual outpatient healthcare costs for RSV infections were estimated to be 7-9 billion JPY (50-64 million USD) for children aged