The tempo‒spatial heterogeneity of the association between hourly ambient temperature and injury morbidity: A nationwide large case-crossover study in China

In the context of global warming, the impact on human health has received increasing attention. However, studies focusing on injury are limited, with most examining temperature-injury association on a daily scale, and the finer temporal variability is unclear. A time-stratified case-crossover study was carried out in 243 surveillance hospitals across China, and ambient temperature was matched to injury cases and controls on an hourly scale. The effects of hourly temperature exposure on injury morbidity were estimated by conditional logistic regressions and meta-analyses, and vulnerable timing and place of injury were further identified. A total of 11,512,467 injury cases were included, with the largest number of cases occurring at 10:00 (1,019,381, 8.85%). The effect of temperature on injury morbidity lasting up to 5 h following exposure, and the cumulative excess risk (CER) of injury increased by 1.04% (95% CI: 0.90%, 1.18%) for each 1 °C rise in hourly temperature. Within a day, temperature-related injury risk peaked at 3:00 (CER = 1.72%, 95% CI: 1.19%, 2.24%), particularly in industrial/construction zones (CER = 1.37%, 95% CI: 1.22%, 1.52%). For injury mechanism, animal-related injury risk was much higher than other injuries across 24 h within a day in all places, especially in industrial/construction zone at 6:00 (CER = 9.37%, 95% CI: 1.12%, 18.30%). The hourly temperatures are acutely associated with an increased risk of injury morbidity, and temperature-related injury risk is more pronounced at nighttime within a day, particularly in industrial and construction zone as well as public place. Our findings provide crucial information for precisely adapting to climate change and reducing injury morbidity.