Associations between mortality from COVID-19 in two Italian regions and outdoor air pollution as assessed through tropospheric nitrogen dioxide

Abstract

After the appearance of COVID-19 in China last December 2019, Italy was the first European country to be severely affected by the outbreak. The first diagnosis in Italy was on February 20, 2020, followed by the establishment of a light and a tight lockdown on February 23 and on March 8, 2020, respectively. The virus spread rapidly, particularly in the North of the country in the 'Padan Plain' area, known as one of the most polluted regions in Europe. Air pollution has been recently hypothesized to enhance the clinical severity of SARS-CoV-2 infection, acting through adverse effects on immunity, induction of respiratory and other chronic disease, upregulation of viral receptor ACE-2, and possible pathogen transportation as a virus carrier. We investigated the association between air pollution and subsequent COVID-19 mortality rates within two Italian regions (Veneto and Emilia-Romagna). We estimated ground-level nitrogen dioxide through its tropospheric levels using data available from the Sentinel-5P satellites of the European Space Agency Copernicus Earth Observation Programme before the lockdown. We then examined COVID-19 mortality rates in relation to the nitrogen dioxide levels at three 14-day lag points after the lockdown, namely March 8, 22 and April 5, 2020. Using a multivariable negative binomial regression model, we found an association between nitrogen dioxide and COVID-19 mortality. Although ecological data provide only weak evidence, these findings indicate an association between air pollution levels and COVID-19 severity.

Keywords: Air pollution; Coronavirus; Covid-19; Mortality; Nitrogen dioxide; Public health.

Graphical abstract

Fig. 1

Average NO₂ tropospheric levels in the study area before the lockdown of February 23, 2020, based on data from the Sentinel-5P mission from Copernicus Earth Observation Programme of the European Space Agency and the European Union.

Fig. 2

Negative binomial regression analysis between nitrogen dioxide (NO₂) tropospheric levels (μmol/m²) before the spread of the outbreak and COVID-19 mortality rate (deaths per 100,000) in the three periods after the lockdown dates (A: February 24–March 8; B: February 24–March 22; C: February 24–April 5). Adjusted COVID-19 mortality rate (solid line) with 95% confidence interval (dash lines) was estimated with a multivariable model, taking into account population density, aging index, people mobility measured from telephone movements before the lockdown, temperature (°C) and relative humidity (%) in the three subsequent periods, and airport presence. Shaded circles are weighted on number of deaths corresponding to the adjusted mortality rates at each time point.