Data collected in early childhood
At the time of the index hospitalization episode, a venous blood sample was obtained for analysis of blood eosinophils, eosinophil cationic protein (ECP) in serum and nasopharyngeal aspirates and total and allergen-specific IgE in serum.14 Eosinophil counts ≥ 0.45 cells × 109/L,18 serum ECP concentration ≥ 16 µg/L,18 nasopharyngeal ECP concentration ≥ 870 ng/g mucus19 and total serum IgE ≥ 60 kU/L14 were considered elevated. The detection limit in the measurement of allergen-specific IgE was 0.35 µg/L.20 Respiratory viruses, including RSV and rhinovirus, were identified using antigen and genome-detection methods. The associations between these viruses and outcomes have been published previously.16,21
The parents of the recruited bronchiolitis patients were interviewed using structured questionnaires during hospitalization and at subsequent follow-up visits four weeks and four months later.18The questionnaires collected data on family histories of asthma and atopy, maternal and paternal histories of smoking, including maternal smoking during pregnancy, childhood histories of wheezing episodes and atopic dermatitis and the presence of household pets. For both children and parents, only asthma and allergies diagnosed by a physician were registered.