Effects of heatwaves on ambulance dispatches in Vienna

Abstract

As noted in the latest IPCC report, the frequency and intensity of heatwaves is increasing, making it necessary to develop preventive measures such as heatwave warning systems. This study aims to identify the effects of heatwaves on ambulance dispatches in Vienna, based on ambulance data provided by MA70, the largest rescue organisation in Vienna, and climate data provided by UBIMET GmbH, an international weather service, based in Vienna. In the investigated time-frame of June, July and August 2018-2021, 218 692 ambulance dispatches were included in the analysis.The effects are stratified by age group and gender, and the diagnoses with the greatest increase in dispatch numbers during heatwaves are identified. In addition, the effect of the first heatwave in each year is compared to that of subsequent heatwaves and the impact of each consecutive heatwave day, as well as potential lag effects of heatwaves, are examined.First, a statistical comparison of dispatch rates on heatwave versus non-heatwave days was conducted to test for a statistically significant increase in daily ambulance dispatches during heatwaves. Second, a regression analysis was performed by using a generalized linear model with negative binomial distribution and a stratified data approach to control for confounders. An overall increase in daily ambulance dispatches was observed during heatwaves. When defining a heatwave as a daily minimum temperature greater than 20.5 ◦C for a minimum duration of 2 days (all subsequent estimates refer to this definition), the daily number of ambulance dispatches increased by 10.4% (IRR = 1.104; 95% CI: [1.077, 1.131]; p < 0.001). An inverse relationship was identified between the magnitude of the heatwave effect and the average number of heatwave days per year. The effect of heatwaves on the daily number of ambulance dispatches was more pronounced for women (IRR = 1.094;95% CI: [1.063, 1.126]; p < 0.001) than for men (IRR = 1.085; 95% CI: [1.052, 1.119]; p < 0.001). Among the age groups, the strongest effects were observed for the age group 0 − 18 (IRR = 1.119; 95% CI: [1.044, 1.198]; p < 0.01), followed by the age group 76 − 85 (IRR = 1.096; 95% CI: [1.047, 1.147]; p < 0.001). The diagnoses of heatstroke (IRR = 1.181; 95% CI: [1.074, 1.298]; p < 0.001), chronic obstructive pulmonary disease (COPD) (IRR = 1.070; 95% CI: [1.032, 1.109]; p < 0.001), unconsciousness (IRR = 1.069; 95% CI: [1.05, 1.088]; p < 0.001), and assault (IRR = 1.073; 95% CI: [1.04, 1.108]; p < 0.001) showed the largest increases in dispatch rates during heatwaves.The first heatwave of the year had a greater effect on the daily number of ambulance dispatches than subsequent heatwaves. In addition, the effect of heatwaves tended to increase with the number of consecutive heatwave days. Lag effects of heatwaves were observed up to 4-5 days after the heatwave. Our results provide an initial analysis to understand the effects of heatwaves on ambulance dispatches in Vienna and suggest that warning systems should be particularly sensitive to the first heatwave of the year, vulnerable population groups such as the young (0-18) and the elderly (76-85) and specific diagnoses including, heatstroke, COPD, unconsciousness and assault.