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Interaction of temperature and relative humidity on emergency room visits for respiratory diseases

To quantitatively evaluate the effect of ambient temperature (AT), relative humidity (RH), and their interaction on emergency room visits (ERVs) for respiratory diseases in Beijing, a generalized additive model (GAM) was used to analyze the exposure-effect relationship between AT, RH and daily respiratory disease (ERVs) from 2009 to 2011 in Beijing, as well as their interaction effect on such visits. The model was considered with some potential confounding factors, such as long time trend, "day of week" effect, holiday effect, and air pollution. An obvious U-shaped pattern was found between temperature and daily respiratory disease (ERVs) with the optimum temperature threshold at 12. Below that optimum temperature threshold, a 1 increase was associated with a decrease of 2.26% (95%CI:-2.43,-2.09) for (ERVs). Above that temperature threshold, a 1 increase was associated with an increase of 0.92% (95%CI: 0.72, 1.11). A U-shaped pattern was also observed between RH and daily respiratory disease (ERVs) with the optimum RH threshold at 51%. Below that RH threshold, the (ERVs) increased by 3.43% (95%CI:-3.47%,-3.38%) for a 10% decrease. Above that RH threshold, the (ERVs) increased by 1.80% (95%CI: 1.76%, 1.85%) for a 10% increase. There was a synergistic effect of temperature and RH on respiratory diseases, which meant that the temperature effect differed by RH level. Below the temperature threshold, the temperature effect was stronger in lower RH levels, and the effect estimate per 1 decrease in temperature was an 2.71% (95%CI:-2.88,-2.53) increase for respiratory disease (ERVs). However, above the temperature threshold, the temperature effect was greater in higher humidity levels, and the effect estimate per 1 increase in temperature was a 1.37% (95%CI: 1.13, 1.61) increase for respiratory disease (ERVs). © 2016, Chinese Society for Environmental Sciences. All right reserved.