Results
Participant
characteristics
The characteristics of the 2,934 participants included in the analysis
sets are shown in Table 1. The cumulative incidence rates of asthma and
wheezing were 10.4% and 38.1%, respectively. The incidence rates of
asthma by age were 2.7%, 4.8%, and 3.0% at 0-12, 12-24, and 24-36
months old, respectively, and were highest at 12-24 months old. The
incidence rates of wheezing by age were 20.0%, 13.6%, and 4.6%,
respectively, and were highest at 0-12 months old.
The total serum IgE level was measured at 24 months old in 2,900
children. The upper tenth percentile of the total serum IgE level in
24-month-old children was 180 IU/mL, and the serum IgE level was high
(≥180 IU/mL) at 9.7% and low (<180 IU/mL) at 90.3%. High
levels of maternal serum IgE were detected in 18.0%, and the rates of
maternal active smoking (36.8 μg/g creatinine or higher) and passive
smoking (0.31 36.8 μg/g-creatinine) based on the urinary creatinine
level were 5.7% and 33.1%, respectively.
Mite allergen and endotoxin
The levels of dust mite allergen and endotoxin in dust are shown in
Table 2. The geometric means of Der 1 per unit area and per gram dust
determined in the analysis were 64.95 µg/m2 and 3.89
µg/g, respectively. The geometric means of endotoxin were
2.71×105 EU/m2 and 16.0 EU/mg,
respectively.
Association of mite allergen with the incidence of asthma or
wheezing
The adjusted ORs of dust mite allergen exposure level Der 1 in the Q2-Q4
groups in comparison with the Q1 group are shown in Fig. 2. The ORs of
the cumulative incidence rates of asthma and wheezing were significantly
higher in the Q4 group during 0-36 months old (OR: 1.85 (95% CI:
1.30-2.63) and OR: 1.33 (95% CI: 1.05-1.67), respectively). The ORs in
the Q2 and Q3 groups were not significant. A significant trend
relationship with Der 1 was noted in the cumulative incidence rates of
asthma and wheezing (Fig. 2).
By onset age, a significant OR was noted in asthma in the Q4 group at
12-24 months old (OR 1.91, 95% CI: 1.17-3.12) and 24-36 months old (OR
1.99, 95% CI: 1.07-3.70). Similarly, a significant OR was noted in
wheezing in the Q4 group during 0-12 months old (OR 1.60, 95% CI:
1.18-2.16). A significant trend was noted at all the aforementioned
onset ages.
Association of endotoxin with the incidence of asthma or
wheezing
The adjusted ORs of the endotoxin exposure level are shown in Fig. 3.
The adjusted OR of the cumulative incidence rate of asthma during 0-36
months old was 1.59 (95% CI: 1.03-2.44) in the Q4 group of the
endotoxin exposure level, indicating significance. The OR (95% CI) of
the cumulative incidence rate of wheezing during 0-36 months old was
significant in the Q2 group of the endotoxin exposure level (OR: 1.28
[95% CI: 1.04-1.57]). In the cumulative incidence rate of asthma, a
significant trend relationship with the exposure level was noted (Fig.
3).
By onset age, the ORs for the onset of asthma (OR 2.00, 95% CI:
1.03-3.85) and wheezing (OR 1.78, 95% CI: 1.01-3.12) were the highest
and significant in the Q4 group during 24-36 months old.
Association of mite allergen or endotoxin with high levels
of total serum IgE
The adjusted ORs for high levels of total serum IgE at 24 months old in
the Q2-Q4 groups of the dust mite allergen exposure level and endotoxin
exposure level in comparison with the Q1 group are shown in Fig. 4. A
significant OR (95% CI) was noted in both dust mite allergen and
endotoxin exposure levels in the Q4 group in comparison with the Q1
group (OR: 1.69 (95% CI: 1.18-2.42) and OR: 1.66 (95% CI: 1.07-2.57),
respectively, but the OR was not significant in the Q2 or Q3 group. A
significant trend was noted for both dust mite allergen and endotoxin
exposure levels. Results of sensitivity analysis of the ‘amount per unit
mass of dust’ are shown in Supp Info Figure 3-5.