The evolution of risk factors for respiratory syncytial virus-related hospitalisation in infants born at 32-35 weeks' gestational age: time-based analysis using data from the FLIP-2 study

Aim: The aim of this study was to examine whether the risk for respiratory syncytial virus (RSV)-related hospitalisation changes through the first year of life in infants of 32-35 weeks' gestational age (wGA). Methods: Risk factors from the FLIP-2 study (190 cases/4566 age-matched controls) were included in a Cox regression analysis wherein time slices were taken at 1-month intervals from birth. Results: Half of all RSV hospitalisations occurred in the first 68 days after birth, with 56% occurring within 90 days. The time taken for 50% of hospitalisations to occur was 148 days for those born outside the RSV season and 58 days for those born within the season. By 90 days old, 84% of infants born in the season and 20% of those born outside the season were hospitalised. In both groups, hospitalisations occurred >= 5 months after birth. Male sex, smoking whilst pregnant, month of birth, duration of breastfeeding, number of siblings at school, and number of smokers in household all contributed to the risk of RSV hospitalisation beyond the age of 90 days. Conclusions: The risk of RSV hospitalisation appears to persist to at least 5-6 months old in 32-35 wGA infants, which has implications for the optimal management of disease prevention.