Hospitalizations for respiratory syncytial virus bronchiolitis in preterm infants at <33 weeks gestation without bronchopulmonary dysplasia: the CASTOR study

Abstract

This study was conducted during the 2008-2009 respiratory syncytial virus (RSV) season in France to compare hospitalization rates for bronchiolitis (RSV-confirmed and all types) between very preterm infants (<33 weeks' gestational age, WGA) without bronchopulmonary dysplasia and full-term infants (39-41 WGA) matched for date of birth, gender and birth location, and to evaluate the country-specific risk factors for bronchiolitis hospitalization. Data on hospitalizations were collected both retrospectively and prospectively for 498 matched infants (249 per group) aged <6 months at the beginning of the RSV season. Compared to full-term infants, preterm infants had a fourfold [95% confidence interval (CI) 1·36-11·80] and a sevenfold (95% CI 2·79-17·57) higher risk of being hospitalized for bronchiolitis, RSV-confirmed and all types, respectively. Prematurity was the only factor that significantly increased the risk of being hospitalized for bronchiolitis. The risk of multiple hospitalizations for bronchiolitis in the same infant significantly increased with male gender and the presence of siblings aged ⩾2 years.

Fig. 1.

Study design. RSV, Respiratory syncytial virus.

Fig. 2.

Disposition of infants. ^a All infants who met inclusion and non-exclusion criteria. ^b All infants who met inclusion and non-exclusion criteria and who were matched.

Fig. 3.

Hospitalizations for bronchiolitis [respiratory syncytial virus (RSV) and in general] during the 2008–2009 RSV season (matched population). ^a Relative risk 7·00 (95% CI 2·79–17·57); ^b relative risk 4·00 (95% CI 1·36–11·80). Two approaches were considered in the sensitivity analysis to handle missing RSV tests: ^c High hypothesis imputed missing RSV tests as positive tests. ^d Crossed hypothesis added a number of adjusted RSV hospitalizations to each study group.