Childhood Asthma and Increased Airway Responsiveness A Relationship That Begins in Infancy

Rationale Asthma is associated with increased airway responsiveness (AR), but the age when this relationship becomes established is not clear. The present study tested the hypothesis that the association between increased AR and asthma is established after 1 month of age. Objectives: To relate AR in infancy to asthma in childhood. Methods: As part of a birth cohort study, AR was determined at 1 (early infancy), 6 (mid-infancy), and 12 months of age (late infancy). At 11 years of age (childhood), AR and the presence of asthma symptoms were determined. Measurements and Main Results: Of the 253 study subjects enrolled, AR was determined in 202 in early infancy, 174 in mid-infancy, 147 in late infancy, and 176 in childhood. Increased AR in late infancy, but not in early or mid-infancy, was associated with increased wheeze at 11 years of age (P = 0.016). Increased AR in infancy persisted into childhood in association with male gender, early respiratory illness, and maternal smoking and asthma. Among the 116 subjects assessed in late infancy and childhood, recent wheeze was present in 35% of children with increased AR at both ages, 13% with increased AR in childhood only, 12% for those with increased AR in late infancy only, and 0% for those who did not have increased AR at either age (P = 0.023); the proportions of children with diagnosed asthma in the corresponding groups were 27, 20, 12, and 0% (P = 0.038). Conclusions: The association between increased infantile AR and childhood asthma emerges at the end of the first year of life.