Inpatient Burden of Respiratory Syncytial Virus Infection and Influenza in Children Younger than 5 years in Japan, 2011-2022: A database study

Background Respiratory syncytial virus (RSV) and influenza virus are major viral etiologies of pediatric lower respiratory tract infection, but comparative data on inpatient burden are lacking. Methods Using a large-scale health claims database in Japan, we identified patients under 5 years of age with a confirmed RSV or influenza diagnosis as an outpatient or inpatient between 2011-2022. Hospitalization rate, inpatient characteristics, various in-hospital outcomes/complications, and healthcare resource utilization were described. Results A total of 176,911 RSV-confirmed outpatients, 153,383 influenza-confirmed outpatients, 90,413 RSV-confirmed hospitalizations, and 11,186 influenza-confirmed hospitalizations were identified. Among outpatients, 24.7% of RSV infection and 2.8% of influenza cases required hospitalization within one week. There was no comorbidities/prematurity for 95.0% of RSV hospitalizations and 96.5% of influenza hospitalizations. Proportions of in-hospital outcomes/complications were (RSV infection vs influenza): oxygen use 47.6% vs 14.8%, mechanical ventilation 2.1% vs 0.7%, pneumonia 33.6% vs 12.8%, otitis media 7.7% vs 2.3%, febrile seizure 1.5% vs 34.4%, encephalitis/encephalopathy 0.1% vs 0.5%, myocarditis <0.1% vs 0.6%, antibiotics prescription 48.0% vs 24.4%. The mean inpatient stay was 6.1 vs 4.3 days at direct medical costs of 435,744 vs 315,809 JPY/patient. These trends held true in age-stratified data. In-hospital death occurred in 31 RSV infection and 6 influenza cases. Conclusions Although both infections resulted in substantial burden, RSV infection led to more frequent hospitalizations, worse in-hospital outcomes, longer inpatient stays, higher medical costs, and more frequent antibiotics prescription compared to influenza. Most RSV hospitalizations occurred among healthy term children, emphasizing the need for prevention measures in all children.