Beyond traffic; PM2.5 and lung function in a rural cohort study of children with asthma

摘要

Background Many studies demonstrate an adverse effect of traffic-derived PM2.5 on children with asthma in urban areas. In agricultural settings, animal operations and crop production are important contributors to PM2.5 but the impacts on childhood asthma are not well characterized. In the Yakima Valley region of Washington State, residents have expressed concerns over the effects of large dairy operations and tree fruit orchards on pediatric asthma morbidity. Aims To determine whether daily lung function of school-aged children with asthma in an agricultural community is associated with ambient PM2.5. Methods Over a two-year period, 58 children with asthma in rural WA State were instructed to provide daily measures of forced expiratory volume in one second (FEV1) using handheld digital peak flow meters. Estimates of exposures to outdoor PM2.5 were determined from a regulatory community monitor in the center of the study region. The effect of 24-hour average PM2.5 on percent predicted FEV1 one day later was modeled using generalized estimating equations (GEE). Interaction terms were included to assess potential effect modification by child's atopy status and overall asthma symptom control. Results Community PM2.5 concentrations ranged from 0.3 to 54.8 ug/m3, with a geometric mean and s.d. of 5.7±2.4 ug/m3. A10 ug/m3 increase in PM2.5 was associated with a 2.2% decrease in FEV1% (95% CI: -0.2, -4.2%) after adjustment for time-varying meteorological covariates. We observed a larger effect for children with atopic asthma (p-value for interaction = 0.12) and for children who demonstrated poorer asthma symptom control than average (p-value for interaction = 0.03). Conclusions Ambient PM2.5 is associated with lung function deficits in this rural cohort where agricultural activities contribute more PM pollution than traditional urban sources, such as traffic. Further characterization of the effects of large-scale agricultural operations on community air quality and the health of vulnerable groups is warranted.