Associations between COVID-19 Incidence Rates and the Exposure to PM2.5 and NO 2 : A Nationwide Observational Study in Italy

The COVID-19 outbreak disproportionately affected the elderly and areas with higher population density. Among the multiple factors possibly involved, a role for air pollution has also been hypothesized. This nationwide observational study demonstrated the significant positive relationship between COVID-19 incidence rates and PM2.5 and NO 2 levels in Italy, both considering the period 2016–2020 and the months of the epidemic, through univariate regression models, after logarithmic transformation of the variables, as the data were not normally distributed. That relationship was confirmed by a multivariate analysis showing the combined effect of the two pollutants, adjusted for the old-age index and population density. An increase in PM2.5 and NO 2 concentrations by one unit (1 µg/m 3 ) corresponded to an increase in incidence rates of 1.56 and 1.24 × 10 4 people, respectively, taking into account the average levels of air pollutants in the period 2016–2020, and 2.79 and 1.24 × 10 4 people during March–May 2020. Considering the entire epidemic period (March–October 2020), these increases were 1.05 and 1.01 × 10 4 people, respectively, and could explain 59% of the variance in COVID-19 incidence rates (R 2 = 0.59). This evidence could support the implementation of targeted responses by focusing on areas with low air quality to mitigate the spread of the disease.