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.