Effects of High Temperature on COVID-19 Deaths in U.S. Counties

The United States of America (USA) was afflicted by extreme heat in the summer of 2021 and some states experienced a record-hot or top-10 hottest summer. Meanwhile, the United States was also one of the countries impacted most by the coronavirus disease 2019 (COVID-19) pandemic. Growing numbers of studies have revealed that meteorological factors such as temperature may influence the number of confirmed COVID-19 cases and deaths. However, the associations between temperature and COVID-19 severity differ in various study areas and periods, especially in periods of high temperatures. Here we choose 119 US counties with large counts of COVID-19 deaths during the summer of 2021 to examine the relationship between COVID-19 deaths and temperature by applying a two-stage epidemiological analytical approach. We also calculate the years of life lost (YLL) owing to COVID-19 and the corresponding values attributable to high temperature exposure. The daily mean temperature is approximately positively correlated with COVID-19 deaths nationwide, with a relative risk of 1.108 (95% confidence interval: 1.046, 1.173) in the 90th percentile of the mean temperature distribution compared with the median temperature. In addition, 0.02 YLL per COVID-19 death attributable to high temperature are estimated at the national level, and distinct spatial variability from -0.10 to 0.08 years is observed in different states. Our results provide new evidence on the relationship between high temperature and COVID-19 deaths, which might help us to understand the underlying modulation of the COVID-19 pandemic by meteorological variables and to develop epidemic policy response strategies.Plain Language Summary The spread of coronavirus disease 2019 (COVID-19) pandemic has become of unparalleled public health concern from the beginning of 2020, especially in the United States of America (USA). In the summer of 2021, extreme heat swept the United States and some states even underwent the hottest or top-10 hottest summer on record. The relationships between high temperature and COVID-19 severity are less discussed compared with other environmental exposures and existing studies show different results. In this research, we focus on COVID-19 deaths and use epidemiological approach to explore the effects of high temperature during the summer of 2021 in the USA. We find an approximately positive association between daily mean temperature and COVID-19 mortality nationally. When temperature get to the 90th percentile from the local median, about 11% increase in the next 7-day cumulative number of COVID-19 deaths is noticed. Different temperature-mortality responses are observed at the region-specific level. The findings of our study suggest that with spatial variations, high temperature could be an important factor influencing the COVID-19 pandemic and might increase the risk of COVID-19 mortality, which would be a useful supplement to assist policymakers to design COVID-19 control measures.