[Intraseasonal variation of the association between cold temperature and mortality risk in Shandong Province]

Objective: To explore the intraseasonal variation in mortality risk from cold temperature exposure in Shandong Province. Methods: Mortality data in Shandong province from 2013 to 2018 were collected from the cause of death surveillance system of Shandong Center for Disease Control and Prevention. The basic information mainly included the date of death, age, gender, education level, cause of death, home address, etc. The daily meteorological data from China Meteorological Data Network mainly included the grid coordinate data of 0.01°×0.01° latitude and longitude, such as daily average temperature (℃) and daily average relative humidity (%). The cold season was from November to February. The first two months were the early cold season and the last two months were the late cold season. The extreme cold temperature was defined as the 10^th percentile of the temperature range of cold season. Time-stratified case crossover design with distributed lag non-linear model analyzed the association between temperature and mortality and the association between extreme low temperature and mortality in different lag days in the cold season, and compared the intraseasonal differences between early (November-December) and late (January-February) cold season. Results: The temperature ranged from -17.3 ℃ to 18.6 ℃ in Shandong Province during the cold season from 2013 to 2018, and the P₁₀ (extreme low temperature) was -13.7 ℃. The average daily temperature in the early cold season was (3.63±4.66) ℃. The temperature in the late cold season was (-0.09±3.70) ℃. The average daily relative humidity was (63.89±14.75) % in the early cold season and (62.27±14.19) % in the late cold season. This study included 1 473 300 deaths in the cold season in Shandong Province between 2013 and 2018. There were 824 601 (55.97%) males and 349 824 (23.75%) cases aged<65 years. There were 803 691 (54.55%) deaths due to circulatory diseases and 140 415 (9.53%) deaths due to respiratory diseases. The results of DLNM showed that the cumulative OR of extreme low temperature in the four months of cold season was 1.74 (95%CI: 1.63, 1.86) with the optimal temperature of 18.6 ℃ as the reference. The cumulative OR values of early and late cold season were 1.50 (95%CI: 1.32, 1.71) and 2.56 (95%CI: 2.12, 3.09), respectively (P<0.001). The lag effect lasted for 12 d. Conclusion: There is an intraseasonal variation of the association between cold temperature and mortality risk in Shandong Province. The mortality risk related to cold temperature in the late cold season is higher than that in the early cold season.