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The risk of asthma and lung function reduction is increased in children who have presented with wheezing associated with respiratory tract infection in early childhood. Three prospective cohort studies consisting of patients hospitalized for infection-associated wheezing at <24 months of age, which started in Finland and Sweden in the 1980`s and 1990`s, have reported outcomes at >25 years of age. These three cohorts are even globally the only cohorts consisting of early-childhood wheezers followed prospectively until adulthood. Initially, the studies were not controlled, and the risk of asthma and reduced lung function and the risk factors in question were assessed by analyses within the cohorts.  Matched population-based controls without wheezing history in early childhood were recruited for the studies in adulthood. One follow-up included only questionnaire data without lung function results. Two studies included control visits, and one of them presented clinical and lung function data, and the other clinical and bronchial reactivity data.  Respiratory syncytial virus was identified on admission in all three post-wheezing cohorts, and rhinoviruses in the newest cohort from the 1990`s. 

The present narrative review summarizes data on asthma and lung function reduction in adults aged >25 years after hospitalization for wheezing at age <24 months compared to population-based controls in the three until now published prospective post-wheezing cohorts. The frequency of doctor-diagnosed asthma varied from 10.3% to 36.6%, and that of self-reported symptom-based asthma from 35.4% to 40.7%. The differences between cases and controls were significant and robust to adjustments with current smoking and allergic rhinitis, which were associated with asthma in all cohorts. One cohort study reported lung function results, and both baseline and post-bronchodilator forced expiratory volumes were lower in cases than in controls. About 10-15% of former early-childhood wheezers presented with irreversible lung function reduction characteristic to chronic obstructive lung disease. Family asthma was associated with current asthma, but other early risk factors, with exception of blood eosinophilia in one cohort, were not anymore predictive.

In conclusion, hospitalization for infection-associated wheezing at <24 months of age was an independently significant risk factor of asthma in adults at >25 years of age.