The spread of 2019-nCoV in China was primarily driven by population density. Comment on “Association between short-term exposure to air pollution and COVID-19 infection: Evidence from China” by Zhu et al.

Abstract

Recently, an article published in the journal Science of the Total Environment and authored by Zhu et al. has claimed the “Association between short-term exposure to air pollution and COVID-19 infection” (doi: https://doi.org/10.1016/j.scitotenv.2020.138704 ). This note shows that the stated dependence between the diffusion of the infection and air pollution may be the result of spurious correlation due to the omission of a common factor, namely, population density. To this end, the relationship between demographic, socio-economic, and environmental conditions and the spread of the novel coronavirus in China is analyzed with spatial regression models on variables deflated by population size. The infection rate - as measured by the number of cases per 100 thousand inhabitants - is found to be strongly related to the population density. At the same time, the association with air pollution is detected with a negative sign, which is difficult to interpret.

Negative Correlation between Altitude and COVID-19 Pandemic in Colombia: A Preliminary Report

“…7 Population and/or population density are known to be common factors for the spread of infectious diseases, and, as expected, have been reported as one of the main components in the amplification of the COVID-19 pandemic. 15,16 In this study, we found that positive cases and deaths for COVID-19 had an apparent correlation with altitude; however, these variables were better explained by population density; this trend can be explained by understanding that the larger the population is, the higher the transportation volumes, economic activity, air pollution, social interactions, and virus infections are.…”

Association between exposure to airborne pollutants and COVID-19 in Los Angeles, United States with ensemble-based dynamic emission model

“…In addition, this is validated by the second sensitivity analysis, where the removal of Los Angeles, i.e., highly polluted, has resulted in a positive association between particulates and corona cases. Chan et al (2020) have observed a positive association between short term exposure to particulates and corona incidences in China, which is contested to be spurious by Copiello and Grillenzoni (2020) . With a systematic review of the literature, Copat et al (2020) point out that PM 2.5 is closely associated with COVID-19 than PM 10 due to the inability of the latter to penetrate type II alveolar cells.…”

Particulate matter and SARS-CoV-2: A possible model of COVID-19 transmission

“…A study involving 120 cities in China showed that a 10 μg/m 3 increase in PM of <2.5 μm in aerodynamic diameter (PM 2.5 ) led to more than a 2% increase in new COVID-19 cases ( Zhu et al, 2020b ). However, it was argued that this rise in COVID-19 infection was related to the high population density rather than the short-term exposure to air pollution ( Copiello and Grillenzoni, 2020 ). PM 10 and PM 2.5 were found to be associated with the COVID-19 incidence in Xiaogan, China ( Li et al, 2020 ).…”