Bronchial hyper-reactivity in young adults after hospitalisation for bronchiolitis in infancy.

Background: Bronchiolitis is associated with asthma persisting until adulthood. While bronchial hyper-reactivity (BHR) is a hallmark of asthma, its occurrence and characteristics after bronchiolitis have been less studied. We aimed to study if BHR differed between young adults hospitalised for bronchiolitis in infancy and control subjects with no such history. Further, we sought to study whether any association between asthma and BHR differed between these two groups.

Methods: This Norwegian historical cohort study included 186 young adults hospitalised for respiratory syncytial virus positive or negative bronchiolitis in infancy during 1996-2001 and 139 matched control subjects. BHR was assessed at 17-20 years by methacholine provocation tests and recorded as dose-response slopes (DRS). Outcomes were analysed by mixed effects regression models.

Results: DRS was higher in the post-bronchiolitis group than in the control group (regression coefficient (β) 0.37; 95% CI 0.01 to 0.73; p=0.045). In both groups combined, current asthma was positively associated with DRS (β 0.98; 95% CI 0.50 to 1.45; p<0.001). Stratified analyses showed that the effect (β) of asthma on BHR was 0.80 (95% CI 0.21 to 1.38; p=0.008) in the post-bronchiolitis group and 1.40 (95% CI 0.58 to 2.23; p=0.001) in the control group. The difference in the association between asthma and BHR across the two groups was not statistically significant (p=0.191 for interaction).

Conclusions: BHR at age 17-20 years was higher in subjects hospitalised for bronchiolitis in infancy than in control subjects. The association between asthma and BHR was not found to differ between the post-bronchiolitis group and the control group, although a possible stronger association in the control group may warrant further study.