AUTHOR=Han Lefei , Zhao Shi , Cao Peihua , Chong Marc K. C. , Wang Jingxuan , He Daihai , Deng Xiaobei , Ran Jinjun 

TITLE=How Transportation Restriction Shapes the Relationship Between Ambient Nitrogen Dioxide and COVID-19 Transmissibility: An Exploratory Analysis

JOURNAL=Frontiers in Public Health

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2021.697491

DOI=10.3389/fpubh.2021.697491

ISSN=2296-2565

ABSTRACT=<p><bold>Background:</bold> Several recent studies reported a positive (statistical) association between ambient nitrogen dioxide (NO<sub>2</sub>) and COVID-19 transmissibility. However, considering the intensive transportation restriction due to lockdown measures that would lead to declines in both ambient NO<sub>2</sub> concentration and COVID-19 spread, the crude or insufficiently adjusted associations between NO<sub>2</sub> and COVID-19 transmissibility might be confounded. This study aimed to investigate whether transportation restriction confounded, mediated, or modified the association between ambient NO<sub>2</sub> and COVID-19 transmissibility.</p><p><bold>Methods:</bold> The time-varying reproduction number (<italic>R</italic><sub><italic>t</italic></sub>) was calculated to quantify the instantaneous COVID-19 transmissibility in 31 Chinese cities from January 1, 2020, to February 29, 2020. For each city, we evaluated the relationships between ambient NO<sub>2</sub>, transportation restriction, and COVID-19 transmission under three scenarios, including simple linear regression, mediation analysis, and adjusting transportation restriction as a confounder. The statistical significance (<italic>p</italic>-value &lt; 0.05) of the three scenarios in 31 cities was summarized.</p><p><bold>Results:</bold> We repeated the crude correlational analysis, and also found the significantly positive association between NO<sub>2</sub> and COVID-19 transmissibility. We found that little evidence supported NO<sub>2</sub> as a mediator between transportation restriction and COVID-19 transmissibility. The association between NO<sub>2</sub> and COVID-19 transmissibility appears less likely after adjusting the effects of transportation restriction.</p><p><bold>Conclusions:</bold> Our findings suggest that the crude association between NO<sub>2</sub> and COVID-19 transmissibility is likely confounded by the transportation restriction in the early COVID-19 outbreak. After adjusting the confounders, the association between NO<sub>2</sub> and COVID-19 transmissibility appears unlikely. Further studies are warranted to validate the findings in other regions.</p>