Effects of Outdoor Air Pollution on School Absenteeism in Taiwanese Children
|Keywords:||空氣污染;缺席;呼吸道疾病;學童;air pollution;school absenteeism;respiratory illness;school children||Issue Date:||2011||Abstract:||
本研究為追蹤性世代研究，研究對象為來自台灣十個具代表性的社區，當中16所國民小學裡共2,915位五年級的學生。在西元2010年8月至西元2011年4月的研究期間，收集研究對象在學期中的缺席資訊，包括缺席次數、日期、缺席原因等。同時，從行政院環保署的空氣品質監測網站上收集研究期間內的空氣污染資料，包含懸浮微粒(PM10、PM2.5)、二氧化硫( SO2)、氮氧化物(NOx)、一氧化氮(NO)、二氧化氮(NO2)、臭氧(O3)及一氧化碳(CO)等空氣污染物的濃度。除了臭氧為計算每日上午10點至下午六點間，八小時的濃度平均值外，其餘的空氣污染物則計算每日的24小時平均值作為當日濃度代表。本研究採用個案交叉研究法(case cross-over study)，同時採用時間分層法(time-stratified strategy)以月作為分層單位來選取對照時間，以分析空氣污染物的濃度與學童缺席風險的相關性。統計方法為條件式羅吉斯迴歸(conditional logistic regression)，以單一污染物迴歸模式進行分析並調整每日的平均氣溫及平均雨量。考量空氣污染的延遲效應(lag effect)，因此使用不同的延遲時間，包括當日(lag 0)、延遲1日、延遲2日及延遲3日(lag 1、lag 2、lag 3 )納入分析。效應的評估是以每升高1單位濃度的一氧化碳，或是每升高10單位濃度的其他污染物，所得的缺席勝算比(odds ratio)來表示。分析時先以社區為單位，探討不同污染物對於各種類的學生缺席之效應。進一步再將單一社區的空氣污染效應，依各社區所在區域加以合併為北區、中區、南區、及東區而得到區域層級的空氣污染效應。
研究期間共計有1,396次缺席發生，且大部分都為因呼吸道疾病而缺席。在以社區為單位分析時，發現NOx、NO及NO2與學童因病缺席，和因呼吸道疾病缺席的風險性有相關。進一步考量區域層級的空氣染效應，並針對NOx、NO及NO2對於學童因病缺席，及因呼吸道疾病缺席的影響加以分析，發現在不同區域之間，此三類污染物的效應各有不同。其中，在包含萬華、平鎮、竹東、及新竹的北區，發現在校正了氣溫和雨量後，NOx、NO及NO2的急性暴露，和學童因病缺席及因呼吸道疾病缺席間都有顯著的相關；且對於這兩類缺席，三種污染物對於缺席影響的最大效應值都發生在暴露當日(lag 0) (因病缺席之勝算比分別為NOx：1.24 (95% CI: 1.13-1.37)，NO：1.41(95% CI: 1.18-1.70)及NO2：1.42(95% CI: 1.19-1.68)；因呼吸道疾病缺席之勝算比分別為NOx：1.20 (95% CI: 1.07-1.34)，NO：1.38(95% CI: 1.12-1.69)及NO2：1.30(95% CI: 1.07-1.59))。在北區，NO2對於因呼吸道疾病缺席的效應在暴露當日為最大值，其後效應隨著延遲時間的增加而從lag0到lag3呈現遞減的趨勢。
本研究發現在台灣北區，NOx、NO及NO2的急性暴露與學童因病缺席，或因呼吸道疾病缺席有相關，且三類污染物的最大效應在暴露當日。在北區，NO2的急性暴露對於因呼吸道疾病缺席的效應，在暴露當日為最高值，其後隨延遲時間增加而從lag 0至lag 3呈現遞減。
Outdoor air pollution had adverse effects on human health. Several studies indicated that outdoor air pollution was associated with respiratory symptoms and morbidity. These respiratory adverse effects on children’s health may lead to school absences in children that affect children’s learning and school performance. To assess the adverse effects of outdoor air pollution on children’s health, illness-related school absences, especially respiratory illness-related absences, was an important outcome. There were few studies for the association between air pollution and school absenteeism, and the results were inconsistent.
The aim of the study was to investigate the effects of outdoor air pollution on school absenteeism among elementary school children in Taiwan, with focus on illness-related and respiratory illness-related school absences.
Materials and Methods:
This was a longitudinal cohort study that recruited 2,915 5th-grade school children from16 elementary schools in 10 communities in Taiwan from August 2010 to April 2011. The information of school absences including absence date, daily counts and causes of school absences were collected. Data of air pollutants including particulate matter with a aerodynamic diameter less than 10 μm (PM10) and 2.5 μm (PM2.5), sulfur dioxide (SO2), nitrogen oxides (NOx), nitrogen monoxide (NO), nitrogen dioxide (NO2), ozone (O3), and carbon monoxide (CO) were obtained from Taiwan Environmental Protection Agency (EPA) air monitoring stations. Except daily 8-h average from 10 am to 6 pm of O3, daily 24-h average concentrations of air pollutants were used. We conducted case-crossover design with time-stratified strategy for control sampling to examine the association between concentrations of air pollutants and the risk of school absences. Conditional logistic regression with single pollutant model was applied in statistic analysis. Daily average ambient temperature and rainfall were adjusted in regression models. Different lag periods including same-day lag (lag0) and 3 single-day lags (lag1, lag2, lag3) were tested. The effect estimates were presented as odds ratios (ORs) per 1 unit increase in CO and per 10 units increase in other pollutants. Single community-level effect estimate of each air pollutant on different types of school absences was obtained for each of ten communities. We further combined community-level effect estimates according to area where the community located, including Northern, Central, Southern and Eastern area to get area-level effect estimate.
There were total 1,396 school absence counts during study period and the most were respiratory illness-related school absences. In single-community level, short-term exposure to NOx, NO and NO2 was associated with the risk of illness-related and respiratory illness-related school absences. In area-level with focus on the effects of NOx, NO and NO2 at different lags on illness-related and respiratory illness-related school absences, the effects varied among areas. In Northern area including communities of Wanhua, Pingzhen, Jhudong and Shinchu, acute exposure to NOx, NO and NO2 was significantly associated with the risks of illness-related and respiratory illness-related school absences. The largest effects of NOx, NO and NO2 on illness-related and respiratory illness-related school absences were all at same-day lag (for illness-related school absences: OR=1.24, 95% confidence interval (CI)=1.13-1.37; OR=1.41, 95% CI=1.18-1.70; OR=1.42, 95% CI=1.19-1.68; for respiratory illness-related school absences: OR=1.20, 95% CI=1.07-1.34; OR=1.38, 95% CI=1.12-1.69; OR=1.30, 95% CI=1.07-1.58, for every 10 ppb increase in NOx, NO and NO2 respectively). As for respiratory illness-related school absences in Northern area, there was a trend of NO2 effect that was largest at same-day lag and decreased with increasing day lags (from lag 0 to lag 3).
This study indicated that in Northern area in Taiwan, short-term exposure to NOx, NO and NO2 was associated with the schoolchildren’s risks of illness-related and respiratory illness-related school absences and the largest effects were at same-day lag. In Northern area, the effect of acute exposure to NO2 on respiratory illness-related school absences was largest at same-day lag and declined with increasing day lags from same-day lag to 3-day lag.
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