Abstract
BackgroundExposure to excessive heat kills more people than any other weather-related phenomenon, aggravates chronic diseases, and causes direct heat illness. Strong associations between extreme heat and health have been identified through increased mortality and hospitalizations and there is growing evidence demonstrating increased emergency department visits and demand for emergency medical services (EMS). The purpose of this study is to build on an existing regional assessment of mortality and hospitalizations by analyzing EMS demand associated with extreme heat, using calls as a health metric, in King County, Washington (WA), for a 6-year period.MethodsRelative-risk and time series analyses were used to characterize the association between heat and EMS calls for May 1 through September 30 of each year for 2007–2012. Two EMS categories, basic life support (BLS) and advanced life support (ALS), were analyzed for the effects of heat on health outcomes and transportation volume, stratified by age. Extreme heat was model-derived as the 95th (29.7 °C) and 99th (36.7 °C) percentile of average county-wide maximum daily humidex for BLS and ALS calls respectively.ResultsRelative-risk analyses revealed an 8 % (95 % CI: 6–9 %) increase in BLS calls, and a 14 % (95 % CI: 9–20 %) increase in ALS calls, on a heat day (29.7 and 36.7 °C humidex, respectively) versus a non-heat day for all ages, all causes. Time series analyses found a 6.6 % increase in BLS calls, and a 3.8 % increase in ALS calls, per unit-humidex increase above the optimum threshold, 40.7 and 39.7 °C humidex respectively. Increases in “no” and “any” transportation were found in both relative risk and time series analyses. Analysis by age category identified significant results for all age groups, with the 15–44 and 45–64 year old age groups showing some of the highest and most frequent increases across health conditions. Multiple specific health conditions were associated with increased risk of an EMS call including abdominal/genito-urinary, alcohol/drug, anaphylaxis/allergy, cardiovascular, metabolic/endocrine, diabetes, neurological, heat illness and dehydration, and psychological conditions.ConclusionsExtreme heat increases the risk of EMS calls in King County, WA, with effects demonstrated in relatively younger populations and more health conditions than those identified in previous analyses.
Highlights
Exposure to excessive heat kills more people than any other weather-related phenomenon, aggravates chronic diseases, and causes direct heat illness
Extreme heat can be defined either as a threshold temperature chosen a priori or as a percentile of previously recorded temperatures for a specific study region. Since the latter definition is generally preferred to allow for location-specific variation of effects [44], we explored the 90th, 95th, and 99th percentile of full-year humidex values and chose the model that resulted in the maximum likelihood of fit with our data for this study based on the Akaike Information Criterion (AIC) [5, 6, 33]
The relative risk of an emergency medical services (EMS) call on a heat day compared with a non-heat day was analyzed using Poisson regression and controlled for annual variation in King County’s population [3, 8]
Summary
Exposure to excessive heat kills more people than any other weather-related phenomenon, aggravates chronic diseases, and causes direct heat illness. The existing literature describing the relationship of extreme heat and EMS calls consistently reports significant increases in risk, despite inconsistent definitions and measures of heat. Most of these studies have occurred outside the United States, including Australia [7, 8, 16], Canada [17, 18], Italy [19], Japan [20], and Switzerland [9]. No studies have examined EMS demand for a comprehensive array of health conditions, in a tiered system where 911 dispatch centers triage calls for basic life support (BLS) and advanced life support (ALS) response teams, or in a U.S metropolitan area with a temperate climate where projections in climate change and vulnerability risk factors may enhance the effects of extreme heat on the population
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