Chapter 11: the infant and toddler with wheezing.

Recurrent wheezing is common in young infants and toddlers with 27% of all children having at least one wheezing episode by the age of 9 years. The initial wheezing episodes in young children often are linked to respiratory infections due to viral pathogens such as respiratory syncytial virus, rhinovirus, human metapneumovirus, and influenza virus. Bacterial colonization of the neonatal airway also may be significant in the late development of recurrent wheeze and asthma. Some 60% of children who wheeze in the first 3 years of life will have resolution of wheezing by age 6 years ("transient early wheezers"). Children who are "transient early wheezers" have reduced lung function, which remains low at age 6 years, although wheezing has ceased when compared with children who have never wheezed. In contrast, "nonatopic wheezers" represent 20% of wheezing toddlers <3 years of age. These children have more frequent symptoms during the 1st year of life and may continue to wheeze through childhood, but, typically, episodes become less frequent by early adolescence. Lung function in "nonatopic wheezers" is slightly lower than in control subjects from birth to 11 years of age, but they do not have bronchial hyperreactivity on methacholine challenge. The third phenotype refers to "atopic wheezing" or wheezing associated with IgE sensitization. This phenotype accounts for the last 20% of wheezing children <3 years of age. These "atopic wheezers" have normal lung function in infancy; however, lung function is reduced by age 6 years and bronchial hyperreactivity typically is observed.