Variables
The questionnaires were sent by mail, filled out by a family member, and sent back by mail. Asthma, allergic rhinitis/conjunctivitis, and atopic dermatitis were the common outcomes. The incidence of asthma, allergic rhinitis/conjunctivitis, or atopic dermatitis was based on a positive response to the question, “Has the child visited a physician with the diagnosis of the disease (bronchial asthma, allergic rhinitis/conjunctivitis, or atopic dermatitis) in the last year?”
Early life infection (due to daycare attendance, the presence of older siblings, and severe airway infection) and developmental adaptations (preterm birth and overweight gain) were used as the main factors. Information on daycare attendance was obtained when the infant was 6 months of age. The daycare attendance records were then analyzed based on a positive response to the question, “Does the child attend a childcare?” The data on the existence of older siblings were defined as having one or more older siblings at 6 months. A history of hospitalization owing to cold/bronchitis/bronchiolitis/pneumonia during the last 12 months was evaluated at 1.5 years 3. Preterm birth was defined as delivery at <37 weeks9. Infant overweight gain was defined as weight gain above the 90th percentile between the weight at birth and the weight at the age of 2.5 divided by the exact number of months between those two measurements. The 90th percentile is used according to a previous report 6. As potential confounding factors, sex, maternal smoking at 6 months, breastfeeding, and early atopic dermatitis at 2.5 years were assessed10. Breastfeeding was defined as feeding ≥4 months11. The evaluated time point of factors was shown in Table S1.