New Evidence from a Hot Climate: Considering Multiple Health Events, Exposure Variables, and Trigger Points for Interventions Related to Health Impacts of High Temperatures

Extreme heat is a public health challenge. The scarcity of directly comparable studies on heat-related mortality and morbidity and the inconsistent identification of exposure variables and threshold temperatures for severe heat incidents hampers a comprehensive assessment of heat burden and the development of strategies aimed at mitigating the impact of heat on health. The current study was designed to statistically link environmental conditions with metrics for different causes of mortality and morbidity during the warm season in Maricopa County, Arizona. Using Poisson regression models that controlled for potential time confounders, temperature-health associations were assessed for a suite of mortality and morbidity events and temperature metrics. Minimum event temperatures, increasing event temperatures, and excess event temperatures were statistically identified to represent different temperatures at which heat-health intervention measures might be activated. The predictive capacity of different exposure metrics at variable lags and smoothers was also evaluated.

We found statistically significant and consistently strong associations of high environmental temperature with all-cause mortality, heat-related mortality, heat-related hospitalization and heat-related ED visits. The temperature at which heat-related morbidity events began to increase was 3-6 degrees (C) lower than that at which heat-related mortality began to increase in this setting. Large contrasts were found for the environmental conditions at which heat-health interventions might be activated based on different conceptualizations of trigger points. Choice of exposure variable significantly altered model performance for some but not all health events.

Consideration of a broader set of health events together with a comprehensive approach to identify threshold temperatures and optimal exposure variables for effects of heat on health revealed a need to identify additional strategies to mitigate the effects of high environmental heat on human health. The health burden associated with high temperatures is expected to become more important based on projections of warming and increasing vulnerability.