We aimed to determine the rates of proven respiratory syncytial virus (RSV) hospitalization and disease severity among children born moderately preterm (MP, gestational age [GA] 32-36 weeks, n = 964), children born full-term (FT, GA 38-42 weeks, n = 572), and children born early preterm (EP, GA <32 weeks, n = 524). Our second aim was to identify risk factors for RSV hospitalization among MP. We extracted data from parental questionnaires and medical records, retrieved from a community-based cohort of children aged 43-49 months. The RSV hospitalization rates of MP were higher than FT (3.9 vs. 1.2 %, relative rate 3.2; 95 % confidence interval (CI) 1.4-7.1) and equal to EP (3.9 vs. 3.2 %, relative rate 1.2; 95 % CI 0.7-2.1). MP were hospitalized at an earlier age than EP. Disease severity (based on the type of treatment and hospitalization length) was equal in all groups. Risk factors for RSV hospitalization in MP were younger age and lower birth weight. In multivariable analyses, shorter GA and passive smoking independently increased the likelihood of RSV hospitalization in MP.
Conclusion: The rates of hospitalization due to proven RSV infection are higher in MP than FT and not different between MP and EP. No difference in disease severity was observed. Among MP, the rates of RSV hospitalization are higher for lower GA and when exposed to passive smoking.