Background: Several recent studies reported a positive (statistical) association between ambient nitrogen dioxide (NO 2 ) and COVID-19 transmissibility. However, considering the intensive transportation restriction due to lockdown measures that would lead to declines in both ambient NO 2 concentration and COVID-19 spread, the crude or insufficiently adjusted associations between NO 2 and COVID-19 transmissibility might be confounded. This study aimed to investigate whether transportation restriction confounded, mediated, or modified the association between ambient NO 2 and COVID-19 transmissibility. Methods: The time-varying reproduction number ( R t ) 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 2 , 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 ( p -value < 0.05) of the three scenarios in 31 cities was summarized. Results: We repeated the crude correlational analysis, and also found the significantly positive association between NO 2 and COVID-19 transmissibility. We found that little evidence supported NO 2 as a mediator between transportation restriction and COVID-19 transmissibility. The association between NO 2 and COVID-19 transmissibility appears less likely after adjusting the effects of transportation restriction. Conclusions: Our findings suggest that the crude association between NO 2 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 2 and COVID-19 transmissibility appears unlikely. Further studies are warranted to validate the findings in other regions.
【저자키워드】 COVID-19, China, Reproduction number, nitrogen dioxide, transportation, 【초록키워드】 lockdown, Spread, Transmissibility, COVID-19 outbreak, Linear regression, Mediation analysis, Intensive, association, Evidence, Concentration, Analysis, Decline, COVID-19 transmission, statistical significance, P -value, Chinese, measure, confounders, positive, ambient, Effect, regions, repeated, statistical, significantly, reported, evaluated, unlikely, supported, calculated, adjusted, appear, less, instantaneous, 【제목키워드】 nitrogen, restriction, shape, relationship, dioxide,