3 | Results
Table 1 shows characteristics of the 150 subjects at enrollment and the remission rate of AD at age 3. According to the SCORAD at enrollment, AD severity was ‘mild’ in 72 (48.0%), ‘moderate’ in 61 (41.0%), and ‘severe’ in 17 (11.0%) children. The remission rate of AD at age 3 was 36.0%. There was no significant difference in the remission rate between boys and girls (p = .529). Sensitization rates to HDM and pollen at age 3 were 52.7% and 35.3%, respectively.
The monthly average level of PM10 exposed to each subject was 47.8 ± 3.9 µg/m3 for the whole study period (Table 2). Average values of ambient NO2, SO2, O3, CO, temperature, and RH for the residential places of the young children were 32.1 ± 3.8 ppb, 5.4 ± 1.2 ppb, 22.8 ± 1.6 ppb, 564.5 ± 63.1 ppb, 12.9 ± 0.5°C, and 63.9 ± 5.1%, respectively.
Table 3 shows the long-term effects of PM10 exposure on AD persistence and inhalant allergen sensitization in young children. The overall hazard ratio (HR) of AD persistence at age 3 was 1.06 [95% confidence interval (CI): 0.99−1.14] due to long-term exposure to PM10 by 1 µg/m3. There was no significant association between PM10 exposure and the incidence of sensitization to HDM or pet allergens at age 3. However, a 1 µg/m3 increase in PM10 exposure significantly increased pollen sensitization at age 3 (HR = 1.19; 95% CI: 1.06 − 1.33).
Effects of PM10 on AD persistence and inhalant allergen sensitizations stratified by severity were then evaluated, because the disease course over time was mostly affected by its severity (Table 4). In children with moderate or severe AD, there were significantly positive associations between AD persistence and long-term exposure to PM10. Furthermore, the higher the SCORAD at enrollment, the greater the PM effect; HR of AD persistence was 1.23 (95% CI: 1.07−1.40) for the moderate group and 1.67 (95% CI: 1.16−2.41) for the severe group by 1 µg/m3 increase of PM10 exposure. However, AD persistence in the mild group was not affected by long-term exposure to PM10.
When effects of ambient PM10 exposure on incidence of HDM sensitization were stratified by severity, there were no statistically significant effects in any subgroups, although theP -value was close to 0.05 in the severe group (HR = 1.45; 95% CI: 0.98−2.13, p = .058). PM exposure was also not associated with sensitization to pet allergens either, regardless of AD severity. Of interest, the effect of ambient PM10 exposure on pollen sensitization was significant in the moderate group (HR = 1.33; 95% CI: 1.08−1.61). In the severe group, the association of ambient PM10 exposure with pollen sensitization could not be evaluated statistically because the number of patients was too small.