Physical distancing implementation, ambient temperature and Covid-19 containment: An observational study in the United States

Cui Guo; Shin Heng Teresa Chan; Changqing Lin; Yiqian Zeng; Yacong Bo; Yumiao Zhang; Shakhaoat Hossain; Jimmy W M Chan; David W Yeung; Alexis K H Lau; Xiang Qian Lao

doi:10.1016/j.scitotenv.2021.147876

Physical distancing implementation, ambient temperature and Covid-19 containment: An observational study in the United States

Sci Total Environ. 2021 Oct 1:789:147876. doi: 10.1016/j.scitotenv.2021.147876. Epub 2021 May 21.

Authors

Affiliations

¹ Jockey Club School of Public Health and Primary Care, the Chinese University of Hong Kong, China.
² Division of Environment and Sustainability, the Hong Kong University of Science and Technology, Hong Kong, China.
³ Institute for the Environment, the Hong Kong University of Science and Technology, Hong Kong, China.
⁴ Division of Environment and Sustainability, the Hong Kong University of Science and Technology, Hong Kong, China; Department of Civil and Environmental Engineering, the Hong Kong University of Science and Technology, Hong Kong, China. Electronic address: alau@ust.hk.
⁵ Jockey Club School of Public Health and Primary Care, the Chinese University of Hong Kong, China. Electronic address: xqlao@cuhk.edu.hk.

Abstract

Governments may relax physical distancing interventions for coronavirus disease 2019 (Covid-19) containment in warm seasons/areas to prevent economic contractions. However, it is not clear whether higher temperature may offset the transmission risk posed by this relaxation. This study aims to investigate the associations of the effective reproductive number (R_t) of Covid-19 with ambient temperature and the implementation of physical distancing interventions in the United States (US). This study included 50 states and one territory of the US with 4,532,650 confirmed cases between 29 January and 31 July 2020. We used an interrupted time-series model with a state-level random intercept for data analysis. An interaction term of 'physical distancing×temperature' was included to examine their interactions. Stratified analyses by temperature and physical distancing implementation were also performed to analyse the modifying effects. The overall median (interquartile range) R_t was 1.2 (1.0-2.3). The implementation of physical distancing was associated with a 12% decrease in the risk of R_t (relative risk [RR]: 0.88, 95% confident interval [CI]: 0.86-0.89), and each 5 °C increase in temperature was associated with a 2% decrease (RR: 0.98, 95%CI: 0.97-0.98). We observed a statistically significant interaction between temperature and physical distancing implementation, but all the RRs were small (close to one). The containing effects of high temperature were attenuated by 5.1% when physical distancing was implemented. The association of COVID-19 R_t with physical distancing implementation was more stable (0.88 vs. 0.89 in days when temperature was low and high, respectively). Increased temperature did not offset the risk of Covid-19 R_t posed by the relaxation of physical distancing implementation. Our study does not recommend relaxing the implementation of physical distancing interventions in warm seasons/areas.

Keywords: Ambient temperature; Covid-19 transmission; Effective reproduction number; Implementation of physical distancing interventions; Interaction effects.

Publication types

Observational Study

MeSH terms

COVID-19*
Humans
Physical Distancing
SARS-CoV-2
Temperature
United States