Lung health and questionnaire data
Health questionnaires were used to determine presence and frequency of
wheeze and its triggers, and physician diagnosed asthma among the
children. These questionnaires were administered at 3 and 6 months
postpartum, repeated every 6 months from ages 1 year to 3 years, then
annually to 5 years. Recurrent wheeze was defined as two or more
episodes of wheeze symptoms in one year between 2-5 years of age. Asthma
diagnosis by age 5 was determined by a pediatric consultant with
expertise in asthma at clinic visits. This diagnosis resulted in three
classifications: definite, possible or no asthma. Children who showed
consistent symptoms and objective evidence of bronchodilator response
(greater than 12% enhancement in FEV1) were classified
as definite asthma. Those who had consistent symptoms but did not
show response to bronchodilator or had no symptoms but showed response
to bronchodilator were classified as possible asthma. In order to
maximize statistical power, we combined definite and possible asthma
cases into a single case group and those with no asthma symptoms as the
control group.
In addition to recurrent wheeze and physician diagnosed asthma,
questionnaires completed by parents at 3, 6, 12, 18, 24, 30 months of
age documented exposures to pre- and postnatal cigarette smoking,
traffic air pollution measured by nitrogen dioxide
(NO2), pet ownership, and breastfeeding duration.
Exposure to NO2 was measured using city-specific land
use regression (LUR) models, while accounting for residential mobility
and temporal variance in ambient concentrations.(22) Estimates of
exposure were measured for each residence reported by participants from
address at conception to the address where the participating child
resided at age 1 year.(22) All measures were temporally adjusted based
on local ambient monitoring data per biweekly basis.(22) NO2 exposure
were grouped into three categories: high, moderate, and low exposure.
High was defined as 1 standard deviation above the mean (z score
> 1), low as 1 standard deviation below the mean (z score
< -1) and moderate exposure fell between high and low groups (
-1 < z score < 1).