Covid-19 spread determinant factors during the early phase pandemic in Italy

Abstract Although the Covid-19 pandemic is more than two-years ongoing, the environmental factors beyond virus transmission are still partially unknown. This statistical study investigates the early phase of pandemic in Italy, as its heterogeneity in pollution levels and climate conditions provides an ideal scenario for an ecological study. The selected period excludes important confounding factors, as different virus variants, restriction policies or vaccines. The short-term relationship between the infection maximum increase and demographic, pollution and meteo-climatic parameters was investigated, including both winter-spring and summer 2020 data, also focusing separately on the two seasonal periods and on North vs Centre-South. Among main results, the importance of population size confirmed social distancing as a key management option. The pollution hazardous role undoubtedly emerged, as NO2 affected infection increase in all the studied scenarios, PM2.5 manifested its impact in North of Italy, while O3 always showed a protective action. Whereas higher temperatures were beneficial, especially in the cold season with also wind and relative humidity, solar irradiance was always relevant, revealing several significant interactions with other co-factors. Presented findings address the importance of the environment in Sars-CoV-2 spread and suggest prevention strategies in crowded areas, especially if highly polluted and weakly exposed to sun.