Associations between apparent temperatures and emergency ambulance calls in Wuxi, China: a time series analysis

Inappropriate apparent temperature (AT) is a major global threat to human health. Although the association between temperature and health has been studied extensively, limited evidence regarding emergency ambulance calls (EACs) is available. Daily emergency department visit records, meteorological data, and air pollutant data were obtained from 1 January 2014 to 31 December 2019. A distributed lag non-linear model was applied to examine the interaction between AT and lagged effects. The analysis was stratified according to disease aetiology, sex, and age. The proportion of EACs attributable to AT was calculated as an indicator of associated burden. A non-linear U-shaped relationship was observed between AT and non-accidental, cardiovascular, and circulatory EACs, with the lowest risk AT occurring at 22.54 °C, 17.12 °C, and 12.74 °C, respectively. High AT effects manifested immediately, whereas low AT effects were delayed. Stratified analysis indicated that males and individuals aged ≥65 years demonstrated heightened sensitivity to both extreme heat (97.5th percentile, 35.98 °C) and cold (2.5th percentile, -1.27 °C), whereas females displayed greater vulnerability to extreme heat [relative risks = 1.16, 95% confidence intervals (CI): 1.04-1.29]. The attributable fraction (AF) for non-accidental EACs in Wuxi was 6.88% (95% CI: 4.09-9.26%), with higher AFs observed for cardiovascular (10.37%) and respiratory (4.94%) emergencies. Moderate thermal variations substantially affected the EACs more than extreme AT conditions. These findings underscore the necessity of implementing early warning mechanisms targeting thermal extremes and developing temperature-regulated public facilities to safeguard vulnerable groups, particularly older citizens, during extreme temperature events.