Background: The relation between lower respiratory tract illnesses in early life caused by the respiratory syncytial virus (RSV) and the subsequent development of wheezing and atopy in childhood is not well understood. We studied this relation in children who had lower respiratory tract illnesses that occurred before 3 years of age.
Methods: Children were enrolled at birth and cases of lower respiratory tract illness were ascertained by a physician. Viral tests were done for specimens collected at the time of the illness. Children were classified into five groups according to type and cause of lower respiratory tract illness. Children were then followed prospectively up to age 13, and we measured frequency of wheezing, pulmonary function, and atopic status (allergy skin-prick tests, serum IgE concentrations).
Findings: RSV lower respiratory tract illnesses were associated with an increased risk of infrequent wheeze (odds ratio 3.2 [95% CI 2.0-5.0], p < 0.001), and an increased risk of frequent wheeze (4.3 [2.2-8.7], p < or = 0.001) by age 6. Risk decreased markedly with age and was not significant by age 13. There was no association between RSV lower respiratory tract illnesses and subsequent atopic status. RSV lower respiratory tract illnesses were associated with significantly lower measurements of forced expiratory volume (2.11 [2.05-2.15], p < or = 0.001) when compared with those of children with no lower respiratory tract illnesses, but there was no difference in forced expiratory volume after inhalation of salbutamol.
Interpretation: RSV lower respiratory tract illnesses in early childhood are an independent risk factor for the subsequent development of wheezing up to age 11 years but not at age 13. This association is not caused by an increased risk of allergic sensitisation.