Background: Wheezing illnesses among young children are common and are a risk factor for asthma. However, determinants of childhood bronchial reactivity, a key feature of asthma, are largely unknown. The aim of this study was to determine how patient characteristics during the first severe virus‐induced wheezing episode are associated with pulmonary function at preschool age.

Methods: Study consisted of 76 children presenting with their first wheezing episode at the ages of 3 to 23 months. At study entry, viral etiology, rhinovirus genome load, atopic and clinical characteristics, and standardized questionnaire were analyzed. At 4‐year follow‐up visit, impulse oscillometry with exercise challenge was performed.

Results: At study entry, the mean age of the children was 12 months (SD 6.0), 57 (75%) were rhinovirus positive, and 22 (30%) were sensitized. At follow‐up visit four years later, the mean age of the children was 60 months (SD 7.9) and 37 (49%) were using asthma medication regularly (discontinued before testing in 25 [68%] children). Bronchial reactivity (≥35% change in mean crude values of resistance) after exercise challenge or bronchodilation was present in nine (12%) children. Children with atopic sensitization at the time of the first wheezing episode were more often likely to develop bronchial reactivity (odds ratio 8.8, P = 0.03) than the children without sensitization. No other significant associations were found.

Conclusions: Atopic sensitization at the time of the first severe wheezing episode is an important early risk factor for increased bronchial reactivity at preschool age.