Comparison of daily mortality effects of outdoor (ambient) air pollution between 1999-2001 and 2006-2008 in Bangkok : time stratified case-crossover study

Abstract

Several case-crossover studies have shown association between ambient air pollution and cardiovascular or respiratory mortality. Thailand has not been done Epidemiological Surveillance System by case-crossover design to continuous monitoring air pollution and mortality. This study aimed 1) to examine the association between ambient air pollution and daily mortality in Bangkok, 2) to compare health effect of air pollution among years 1999-2001 and 2006-2008. 3) to compare the applicability of case-crossover design in this study with other design as time series study. Time-stratified case-crossover analysis was used to evaluate the short term effects of ambient air pollution (Nitrogen dioxide (NO₂), Ozone (O₃), Carbon monoxide (CO), Sulfur dioxide (SO₂) and Particulate matter 10 μg/m³ (PM₁₀)) on natural, cardiovascular and respiratory mortality. Controls period were selected by matched days of the week in the same month. Time dependent variables such as temperature today (lag0) and humidity yesterday (lag1) for non-external mortality model, circulatory mortality and respiratory mortality we used moving average of humidity as adjustor in the model of conditional logistic regression analyses. 228,103 non-external deaths in study periods were included. The findings for non-external mortality showed statistically significant associations with PM₁₀ CO and NO₂ in adjusted models, adjusted OR 1.008 ( 95 %CI 1.004-1.012) adjusted OR 1.002 (95 %CI 1.001-1.004) and adjusted OR 1.008 ( 95 %CI 1.003-1.013) respectively. Carbon monoxide has a difference effect between 2 periods with statistically significant (P-value 0.01), specially for period two has effect on non-external mortality than period one. Ozone level was significant increasing. PM₁₀ CO NO₂ and O₃ (8 hours) have effected on circulatory mortality in adjusted model but respiratory mortality did not. This study showed precise air pollutions in 2006-2008 were more problems than 1999-2001 and statistic significant association. The both methods, time series study and case-crossover study provide generally similar evidence. The using both methods to estimated adverse health effect from air pollution are increasing the strong estimation models.