Association between daily ambient air pollution and respiratory symptoms in children with asthma and healthy children in western Japan

<i>Objective</i>: In recent years, air pollutant concentrations in Japan have decreased slightly; however, there are growing concerns about the influences of transnational air pollution on respiratory illness. We aimed to clarify the short-term association between the ambient air pollution and respiratory symptoms among children without asthma, children with asthma not using long-term medications (CA-nonLTM), and those using them (CA-LTM). <i>Methods</i>: A total of 138 children attending 2 primary schools and 71 children with asthma regularly visiting cooperating medical institutions were recruited. Study participants measured peak expiratory flow (PEF) twice a day and recorded coughing, nasal symptoms, and medication use in a diary. Predicted associations between daily air pollutant concentrations and respiratory symptoms, and PEF were evaluated using case-crossover and generalized estimate equation models. <i>Results</i>: Changes in %maxPEF per 10 ppb oxidant (Ox) increase in children without asthma, CA-nonLTM, and CA-LTM were −0.26% (95% CI: −0.49, −0.03), −0.51% (95% CI: −0.89, −0.12), and −0.20% (95% CI: −0.42, 0.01), respectively. The odds ratios for coughing per 10 ppb Ox increase in the Lag0 model were 1.34 (95% CI: 1.11, 1.60), 1.52 (95% CI: 1.12, 2.07), and 1.06 (95% CI: 0.93, 1.20), respectively. These suggested that the Ox concentration has graded effects on %maxPEF and coughing, in the following descending order, CA-nonLTM, children without asthma, and CA-LTM. The Ox concentration was also positively associated with nasal symptoms in children without asthma and CA-LTM. <i>Conclusion</i>: Our results suggest that using long-term medications to manage asthma may play an important role in preventing exacerbation of respiratory symptoms due to air pollution.

<i>研究目的</i>：近年来，日本国内空气污染物浓度已小幅下降，但跨国大气污染对呼吸系统疾病的影响正日益受到广泛关注。本研究旨在明确环境空气污染（ambient air pollution）与三类儿童的呼吸道症状之间的短期关联：无哮喘儿童、未使用长期药物的哮喘儿童（children with asthma not using long-term medications, CA-nonLTM），以及使用长期药物的哮喘儿童（those using them, CA-LTM）。
<i>研究方法</i>：本研究共招募138名就读于2所小学的儿童，以及71名定期前往合作医疗机构就诊的哮喘儿童。所有研究对象每日自行测量两次峰流速（peak expiratory flow, PEF），并在日记中记录咳嗽、鼻部症状及用药情况。本研究采用病例交叉（case-crossover）设计与广义估计方程（generalized estimate equation）模型，评估每日空气污染物浓度与呼吸道症状、峰流速之间的预期关联。
<i>研究结果</i>：每升高10 ppb氧化剂（oxidant, Ox）时，无哮喘儿童、CA-nonLTM组及CA-LTM组的最大峰流速百分比（%maxPEF）变化量分别为-0.26%（95% CI：-0.49, -0.03）、-0.51%（95% CI：-0.89, -0.12）与-0.20%（95% CI：-0.42, 0.01）。在Lag0模型中，每升高10 ppb Ox，咳嗽症状的比值比（odds ratios）分别为1.34（95% CI：1.11, 1.60）、1.52（95% CI：1.12, 2.07）与1.06（95% CI：0.93, 1.20）。结果显示，Ox浓度对%maxPEF与咳嗽症状存在分级效应，按效应强度从高到低依次为CA-nonLTM组、无哮喘儿童组、CA-LTM组。此外，Ox浓度与无哮喘儿童及CA-LTM组的鼻部症状呈正相关。
<i>研究结论</i>：本研究结果表明，使用长期药物管理哮喘，或可在预防空气污染引发的呼吸道症状加重方面发挥重要作用。