Study on the association between heatwaves and road traffic injury mortality in five provinces of China

Objective: To evaluate the impact of short-term exposure to daytime heatwaves, nighttime heatwaves, and compound heatwaves on the risk of road traffic mortality and calculate the attributable mortality burden.

Methods: This study collected road traffic mortality data from the Disease Surveillance System in Guangdong, Hunan, Zhejiang, Yunnan, and Jilin Provinces from 2013 to 2018. A time-stratified case-crossover design was used in this study, with the death date for each case serving as the case day. Control days were selected from the same year, month, and day of the week as the case day. A conditional logistic regression model was employed to estimate the cumulative associations of short-term exposure to daytime heatwaves, nighttime heatwaves, and compound heatwaves on the risk of road traffic mortality (lag 0-1 day) and to calculate the attributable fractions (AF).

Results: Compared to non-heatwave days, the excess risk (ER) of road traffic mortality on daytime heatwave days, nighttime heatwave days, and compound heatwave days was 5.3% (95%CI: 0.5%-10.2%), 4.9% (95%CI: 0.5%-9.4%) and 7.5% (95%CI: 2.3%- 12.9%), with corresponding AF of 5.0% (95%CI: 0.5%-9.3%), 4.7% (95%CI: 0.5%-8.6%), and 6.9% (95%CI: 2.3%-11.4%), respectively. Stratified analysis showed that the risk of traffic mortalities caused by daytime heatwaves was higher in females (ER=15.7%, 95%CI: 5.8%-26.5%) than in males (ER=1.8%, 95%CI: -3.6%-7.4%). Elderly individuals over 64 years old (ER=10.9%, 95%CI: 0.3%- 22.6%) had a higher risk of road traffic mortalities from compound heatwaves than those under 45 years old (ER=2.6%, 95%CI: -5.4%-11.2%). The risk of road traffic injury mortality from motor vehicle accidents caused by compound heatwaves (ER=16.6%, 95%CI:2.4%-32.7%) was higher than that from non-motor vehicle accidents (ER=5.7%, 95%CI:0.1%-11.5%).

Conclusions: Short-term exposure to daytime heatwaves, nighttime heatwaves, and compound heatwaves was associated with an increased risk of road traffic mortality, with the strongest association observed for compound heatwaves. The mortality burden attributable to compound heatwaves was higher than that for daytime and nighttime heatwaves. Heatwaves were more significantly associated with road traffic mortality risk among females, elderly individuals over 64 years old, and motor vehicle accidents.