Following up infant bronchiolitis patients provided new evidence for and against the united airway disease hypothesis.

Aim: The united airway disease (UAD) hypothesis suggests that allergic rhinitis and asthma develop together. We evaluated the evidence for and against the UAD hypothesis at five to seven years of age after hospitalisation for bronchiolitis at less than six months.

Methods: This study used prospective follow-up data for 102 children hospitalised for bronchiolitis under the age of six months. We included the presence of previous and current asthma, prolonged rhinitis and skin prick tests (SPT) to common inhaled allergens and lung function by impulse oscillometry (IOS) at five to seven years of age. Bronchial hyper-reactivity (BHR) was assessed using the exercise challenge test and bronchodilation test.

Results: Current asthma, but not previous transient asthma, was associated with prolonged rhinitis and a positive SPT. BHR, which reflected reactive airways, but not lung function, was associated with respiratory allergy, namely the combination of current asthma, prolonged rhinitis and a positive SPT.

Conclusion: This post-bronchiolitis follow-up study suggested an association between respiratory allergy and reactive airways at five to seven years of age, which supported the UAD hypothesis. However, previous transient asthma and a reduction in lung function reduction did not support the hypothesis.