COVID-19 pandemic increased the magnitude of mortality risks associated with cold temperature in Italy: A nationwide time-stratified case-crossover study

Yu, W.; Xu, R.; Ye, T.; Han, C.; Li, S.; Guo, Y.

Abstract Backgrounds: The coronavirus disease 2019 (COVID-19) pandemic and some containment measures have changed many people lives and behaviours. Whether the pandemic could change the association between cold temperature and mortality remains unknown. Objectives: We aimed to assess whether the association between cold temperature and all-cause mortality in the pandemic period has changed compared to non-COVID-19 period (2015-2019) in Italy. Methods: We collected daily all-cause mortality data and meteorological data for 107 Italian provinces from 1, January 2015 to 31, May 2020. A time-stratified case-crossover design with the distributed lag non-linear model was used to examine the association between cold temperature and all-cause mortality during the first three months (from March to May in 2020) of the COVID-19 outbreak and the same months in 2015-2019. Results: The relative risk (RR) of all-cause mortality at extreme cold temperature (2.5th percentile of temperature at 3 {degrees}C) in comparison with the minimum mortality temperature (24 {degrees}C) was 4.75 [95% confidence interval (CI): 3.90-5.79] in the pandemic period, which is more than triple higher than RR [1.41 (95%CI: 1.33-1.50)] in the same months during 2015-2019. The shift in cold-mortality association was particularly significant for people aged 65-74 years [RR (95%CI): 5.98 (3.78-9.46) in 2020 versus 1.29 (1.10-1.51) in 2015-2019], 75-84 years [5.25 (3.79-7.26) versus 1.40 (1.25-1.56)], and [≥] 85 years [5.03 (3.90-6.51) versus 1.52 (1.39-1.66)], but not significant for those aged 0-64 years [1.95 (1.17-3.24) versus 1.24 (1.05-1.48)]. Conclusion: The findings suggest that the COVID-19 pandemic enhanced the risk of cold temperature on mortality in Italy, particularly among the elderly people. Further studies are warranted to understand the exact mechanism when detailed data are available.