Time-series study on association between heatwaves and emergency ambulance calls: taking Dezhou city, Shandong province as an example

Objective To quantify the association between heatwaves and emergency ambulance calls in Dezhou city and to provide a more comprehensive insight into the health risk evaluation of extreme weather. Methods The data on daily records of emergency ambulance calls, meteorological factors, and air pollution from 2020 to 2022 in Dezhou city, Shandong province were collected. Heatwaves were defined by combining thresholds at the 90th, 92.5th, 95th, or 97.5th percentiles of the year-round daily mean temperature during 2020–2022 and durations of ≥2, 3, or 4 consecutive days, respectively. A generalized additive model with a distributed lag nonlinear model was used to estimate the relative risk of emergency ambulance calls during heatwave days compared with nonheatwave days. Results The impact of heatwaves on emergency ambulance calls lasted up to 7 days, with a cumulative relative risk of 1.12 (95%CI: 1.07, 1.17) for P90_2d. The effect of heatwaves increased significantly with increasing temperature thresholds and durations. There was no difference in the cumulative effect of heatwaves between sexes, while the older population aged 65 and above was more susceptible across age groups, with a relative risk of 1.60 (95%CI: 1.42, 1.81) for the most severe heatwaves. Respiratory diseases were most strongly associated with heatwaves among different disease causes of emergency calls, and the association increased with more severe heatwave types. Conclusion Heatwaves could significantly increase the risk of emergency ambulance calls. The elderly population aged 65 and above is particularly vulnerable to the harmful effects of heatwaves, and those with respiratory illnesses need to be particularly aware of the health risks of heatwaves.

研究目的：量化德州市热浪与急诊救护车呼救事件的关联，为极端天气健康风险评估提供更全面的视角。
研究方法：收集山东省德州市2020至2022年的急诊救护车呼救每日记录、气象因素及空气污染数据。热浪的定义结合了2020-2022年全年日平均气温的90th、92.5th、95th或97.5th百分位阈值，以及连续时长≥2、3或4天的判定标准。采用带有分布滞后非线性模型（Distributed Lag Nonlinear Model, DLNM）的广义相加模型（Generalized Additive Model, GAM），估算热浪日相较于非热浪日的急诊救护车呼救相对风险。
研究结果：热浪对急诊救护车呼救的影响可持续长达7天，其中P90_2d组的累积相对风险为1.12（95%CI: 1.07, 1.17）。热浪的影响随气温阈值与持续时长的升高显著增强。不同性别间热浪的累积效应无显著差异，但在各年龄组中，65岁及以上老年人群的易感性更高，最严重热浪场景下的相对风险达1.60（95%CI: 1.42, 1.81）。在不同病因分类的急诊呼救中，呼吸系统疾病与热浪的关联最为显著，且该关联随热浪严重程度的提升而增强。
研究结论：热浪可显著提升急诊救护车呼救事件的发生风险。65岁及以上老年人群尤其易受热浪的有害影响，呼吸系统疾病患者需格外警惕热浪带来的健康风险。