Severe respiratory syncytial virus infection in preterm infants and later onset of asthma

Background: Respiratory syncytial virus (RSV) is the leading cause of viral lower respiratory tract infections in infants. Preterm infants are at increased risk for hospitalization with RSV (RSV-H), but there are few data on the relationship between RSV-H and asthma in preterm infants, or any data stratified by gestational age, and most studies have short follow-up periods. We sought to evaluate the relationship between serious RSV illness and onset of asthma up to 5 years of age in a cohort of preterm children and to quantify this association. Methods: A retrospective birth cohort of preterm infants (29 weeks 0 days to 35 weeks 6 days gestational age) was constructed from a provincial population-based database, and children were followed forward for 5 years. Incidence rates of RSV-H and asthma were determined. In a Cox proportional hazards model, controlled for putative confounding factors for asthma, the hazard ratio and 95% CI of asthma in children with and without RSV-H was evaluated. Results: Among 3916 premature children, the incidence rate of RSV-H was 25/1000 infants. The cumulative incidence rate of asthma at 5 years of age in children with RSV-H was 57.9/1000 person-years compared with 36.7 in those without RSV-H; the adjusted hazards ratio for asthma in RSV-H infants was elevated at 1.58 (95% CI: 1.03-2.41). Conclusions: In prematurely born children, there is a moderate association between severe RSV infection, as measured by RSV-H in the first year of life, and asthma up to 5 years of age.