Factors Associated With Hospitalization, Length of Stay, and Hospital Expenditures for Respiratory Syncytial Virus Infection in Japanese Infants and Children According to Palivizumab-indicated Underlying Conditions: The LIFE Study.

BACKGROUND Respiratory syncytial virus (RSV) is a major cause of pediatric respiratory tract infections. In Japan, children with specific underlying conditions are eligible to receive palivizumab to prevent severe RSV disease. However, the association between palivizumab eligibility and RSV infection severity remains unclear. This study examined RSV infection severity and hospitalization outcomes in Japanese infants and children according to palivizumab eligibility and identified their associated factors. METHODS Using insurance claims data from 12 municipalities, we identified RSV cases aged ≤24 months between April 2017 and March 2022. The patients' characteristics and hospitalization status were analyzed according to the presence of palivizumab-indicated underlying conditions. Regression models were used to identify factors associated with hospitalization, length of stay (LOS), and hospital expenditures. RESULTS We analyzed 1025 first-time RSV cases (860 infants <12 months and 165 children 12-24 months old). There were 777 (90.3%) palivizumab-ineligible infants and 83 (9.7%) palivizumab-eligible infants. Only 13 (15.7%) palivizumab-eligible infants had received palivizumab in the month before RSV infection, and 8 required hospitalization. RSV hospitalization was significantly associated with age (odds ratio: 0.84, 95% confidence interval: 0.79-0.88), palivizumab-indicated underlying conditions (1.82, 1.13-2.89), and non-indicated high-risk conditions (4.87, 2.28-10.99). These factors were also associated with LOS. Hospital expenditures were associated with age, high-risk conditions and LOS. CONCLUSIONS Palivizumab-indicated underlying conditions, high-risk conditions, and younger age are risk factors for RSV hospitalization. Most hospitalized patients did not receive palivizumab in the month before RSV infection despite being eligible, suggesting that some hospitalizations were preventable through appropriate palivizumab use.