Comparison of total suspended particulate concentration-response relationships for respiratory symptoms between Chinese children with a different susceptibility status.

Few studies have explored concentration-response (C-R) relationships between levels of particulate matter (PM) and respiratory morbidity in terms of the susceptibility of children to respiratory diseases. We sought to determine whether the shapes of C-R curves for comparing total suspended particle (TSP) concentration versus the adjusted prevalence of bronchitis (persistent cough or phlegm) and asthma (current wheeze or asthma) symptoms between children with a different susceptibility status. We used the restricted cubic spline (RCS) function to characterize the C-R relationships between TSP and the adjusted prevalence rates of four respiratory symptoms, after controlling for possible confounding by SO(2) and NO(2) levels, in 11,860 children selected from 18 districts of six cities in Liaoning province. Susceptible children exhibited a 2- to 3-fold elevation in the prevalence of all four respiratory symptoms across the entire TSP range (188-689μg/m(3)). Significant differences in the shapes of C-R curves were evident in children with symptoms of bronchitis (ballistic "S"-shaped curves) and asthma (flattened "U"-shaped curves), as well as between the low and high TSP ranges of such curves, when children were grouped by susceptibility status. A significant linear association between TSP levels and current asthma prevalence was found only among susceptible children exposed to high levels of TSP. The shapes and properties of the TSP-morbidity C-R curves differed significantly by type of respiratory symptom, susceptibility status, and TSP range. More work is required to characterize CR relationships in terms of susceptibility status in countries with different PM levels. Copyright Â