标题：The Influence of Socioeconomic Markers on the Association Between Fine Particulate Matter and Hospital Admissions for Respiratory Conditions Among Children
摘要：Objectives. We evaluated the influence of socioeconomic status (SES) on hospital admissions for respiratory conditions associated with ambient particulate matter that is 2.5 micrometers or less in aerodynamic diameter (PM2.5) in children aged 1 to 9 years in 12 California counties, from 2000 to 2005. Methods. We linked daily hospital admissions for respiratory conditions (acute respiratory infections, pneumonia, and asthma) to meteorological, air pollution, and census data. Results. In San Diego, San Bernardino, Riverside, and Los Angeles counties, the admission rates for children associated with PM2.5 ranged from 1.03 to 1.07 for combined respiratory conditions and 1.03 to 1.08 for asthma in regions with lower SES. We observed 2 distinct patterns of the influence of the composite SES Townsend index. In lower-SES South Coast areas, PM2.5-associated hospital admission rates for all respiratory outcomes were predominantly positive whereas results in the Central Valley were variable, often tending toward the null. Conclusions. These distinct patterns could be attributed to the heterogeneity of regional confounders as well as the seasonal variation of emission sources of PM2.5. Composite SES is one potential factor for increasing susceptibility to air pollution. Growing evidence demonstrates that exposure to ambient particulate matter that is 2.5 micrometers or less in aerodynamic diameter (PM2.5) may be associated with increases in respiratory symptoms and prevalence of asthma in children. 1–4 Children, especially those with preexisting respiratory conditions, may be more affected by ambient PM2.5 than adults. 5 Children are more active and spend more time outdoors, which contributes to their potential for breathing a greater amount of polluted air per pound of body weight than adults. 5,6 Biologically, the peripheral airways in children are more susceptible to inflammation when exposed to polluted air, which leads to greater airway obstruction than in adults. 7 Adding to the public health concern for children and their vulnerability to air pollution, epidemiological studies have revealed that low socioeconomic status (SES) may be associated with different air pollution impacts. A study by Lynch et al. 8 found that persons of lower SES have a generally higher mortality rate than more advantaged persons. To date, most of the epidemiological studies on air pollution exposures have mainly focused on adult mortality rates 9–12 and childhood asthma hospital admissions. 13–16 Studies have shown that low-income families have a higher likelihood of living in older areas and live in high-traffic areas, leading to an increased likelihood of exposure to air toxins and higher ambient PM2.5 compared with high-income families. 17 Questions, however, still remain regarding the role SES plays in the association between ambient PM2.5 and poor respiratory health. For children, a key question is the contribution of low SES to a child’s respiratory health in conjunction with a higher rate of exposure to ambient air pollution. 5–7 Few studies have focused on morbidity among children in relation to ambient concentrations of PM2.5 using a time-series approach. This is probably because the number of hospital admissions for pediatric morbidity is often insufficient for such an analysis. To assess the relationship among SES, acute PM2.5 exposure, and childhood morbidity, we obtained daily hospital admissions and PM2.5 data for the Central Valley and the South Coast regions of California. We also explored which single or composite socioeconomic measures can be used to evaluate socioeconomic inequality in children. We then evaluated the modifying effect of the selected single or composite socioeconomic variables on the association between daily ambient PM2.5 and hospital admissions for respiratory conditions among children from ages 1 to 9 years in 12 counties in the Central Valley and the South Coast regions from 2000 to 2005.
