The Added Effects of Heatwaves on Cause-specific Mortality: A Nationwide Analysis in 272 Chinese Cities

Background: The evidence was limited and inconclusive about the added effects of heatwaves, especially in developing countries.

Objective: To evaluate the added effects of heatwaves on cause-specific mortality in China.

Methods: We designed a nationwide time-series analysis based on daily data from 272 main Chinese cities to from 2013 to 2015. We adopted 12 definitions by combining 4 heat thresholds (90th, 92.5th, 95th, 97.5th percentile of city-specific daily mean temperature) and duration of ≥2, 3 and 4 days. We applied overdispersed generalized additive models with distributed lag models to estimate the city-specific cumulative effects of heatwaves over lags of 0-10 days after controlling for daily temperature. We then, used a meta-regression model to pool the effect estimates at national and regional levels.

Results: Heatwaves could significantly increase risk for mortality from total and cardiopulmonary diseases, including coronary heart disease, ischemic stroke (rather than hemorrhagic stroke) and chronic obstructive pulmonary disease. The effects increased with higher thresholds, but were not appreciably influenced by the duration of heat. The risks generally occurred immediately and lasted for 3 to 5 days. The risks were much larger in the temperate continental zone and the temperate monsoon zones than in the subtropical monsoon zone where there was an evident mortality displacement. The elderly, females and less-educated people were more vulnerable.

Conclusions: This analysis provided ample evidence for the added mortality risk associated with heatwaves, which had important implications for designing heatwave-warning systems and predicting the disease burden of future heatwaves.