Air pollution and respiratory symptoms: Results from three panel studies in Bangkok, Thailand

Several studies in North American cities have reported associations between air pollution and respiratory symptoms. Replicating these studies in citie s with very different population and weather characteristics is a useful wa y of addressing uncertainties and strengthening inferences of causality. To this end we examined the responses of three different panels to particulat e matter (PM) air pollution in Bangkok, Thailand, a tropical city character ized by a very warm and humid climate. Panels of schoolchildren, nurses, an d adults were asked to report daily upper and lower respiratory symptoms fo r 3 months. Concentrations of daily PM10 (PM with a mass median aerodynamic diameter less than 10 mum) and PM2.5 (airborne particles with aerodynamic diameters less than 2.5 mum) were collected at two sites. Generally, associ ations were found between these pollution metrics and the daily occurrence of both upper and lower respiratory symptoms in each of the panels. For exa mple, an interquartile increase of 45 mug/m(3) in PM10 was associated with about a 50% increase in lower respiratory symptoms in the panel of highly e xposed adults, about 30% in the children, and about 15% in the nurses. Thes e estimates were not appreciably altered by changes in the specification of weather variables, stratification by temperature, or inclusion of individu al characteristics in the models; however, time trends in the data cause so me uncertainty about the magnitude of the effect of PM on respiratory sympt oms. These pollutants were also associated with the first day of a symptom episode in both adult panels but not in children. The estimated odds ratios are generally consistent with and slightly higher than the findings of pre vious studies conducted in the United States.