Associations between COVID-19 Incidence Rates and the Exposure to PM2.5 and NO₂: 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 NO₂ 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 NO₂ concentrations by one unit (1 µg/m³) corresponded to an increase in incidence rates of 1.56 and 1.24 × 10⁴ people, respectively, taking into account the average levels of air pollutants in the period 2016-2020, and 2.79 and 1.24 × 10⁴ people during March-May 2020. Considering the entire epidemic period (March-October 2020), these increases were 1.05 and 1.01 × 10⁴ people, respectively, and could explain 59% of the variance in COVID-19 incidence rates (R² = 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.