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.