Healthy Late-preterm infants born 33-36+6 weeks gestational age have higher risk for respiratory syncytial virus hospitalization

Background: Respiratory syncytial virus (RSV) is a leading cause of hospitalization for children <1 year old and is more severe in premature infants. Objective: To assess whether late preterm (LPT) birth is an independent risk factor for RSV hospitalization and more severe RSV disease in children less than 24 months old. Methods: We conducted a retrospective cohort study of children enrolled in the military health system. LPT birth was defined as 33 + 0 through 36 + 6 weeks gestation. Patients who received palivizumab or had known risk factors for RSV were excluded. Adjusted hazard ratios (HR) for LPT birth were calculated using a Cox proportional hazard model, while controlling for sex and RSV season. Severity of illness was assessed by comparing the need for respiratory support, length of stay, and age at RSV hospitalization between LPT and term children. Results: A total of 599,535 children for 1,216,382 person-years were studied, of which 7597 children were admitted for RSV infection. LPT infants accounted for 643 (8.5%) of these RSV hospitalizations. The incidence density for RSV hospitalization of LPT infants was higher than term children (12.1 vs 7.8 per 1000 person-years). LPT infants had an increased adjusted risk for RSV hospitalization; specifically, those born 33 + 0 through 34 + 6 weeks (HR 2.45; 95% confidence interval (CI) 1.96-3.07), and 35 + 0 through 36 + 6 weeks (HR, 1.92; 95% CI, 1.66-222). LPT infants had longer hospital stays and required more respiratory support than term children. Conclusions: LPT birth is an independent risk factor for severe RSV disease and need for hospitalization. Published by Elsevier Ireland Ltd.