COVID-19 epidemic spread and green areas Italy and Spain between 2020 and 2021: An observational multi-country retrospective study

Several studies have proposed that environmental factors influencing human wellbeing, such as chronic exposures to high levels of particulate matter, could indirectly or even directly affect also the severity of COVID-19 disease in case of infection by novel coronavirus SARS-COV2. This study has investigated the association between COVID-19 infections, hospitalizations or deaths and the extension of public green areas (km2 per 100,000 based on OECD data of 2014), an indicator that has been chosen as independent endpoint variable to test the research hypothesis in 10 Italian and 8 Spanish Provinces with more than 500.000 inhabitants, including capitals (Rome and Madrid) and bigger cities (Bologna, Catania, Florence, Genoa, Milan, Naples, Palermo, Turin and Venice for Italy; Barcelona, Valencia, Seville, Zaragoza, Malaga, Las Palmas and Bilbao for Spain). Two different methodologies have been applied: a bottom-up approach was applied to Spanish institutional data concerning contagions/hospitalizations/deaths and the extent of public green areas for each responder to an official questionnaire in the frame of a nationwide survey (with detailed data granularity per province) containing specific georeferenced information; a top-down approach was used for Italy, starting from the official figures of contagions/hospitalizations/deaths of each province and linking them to the OECD statistics about the extension of public green areas in the different areas. Linear and generalized models were used for statistical analyses including also PM2.5 in a multivariate approach (with annual average concentrations from official air quality monitoring stations) and were able to adjust for the different number inhabitants living in each province, in order to take into account the difference in contagion dynamics related to the different density of population. The results obtained for Spain are consistent with those observed for Italy, as for both countries, it has clearly emerged a statistically significant association between COVID-19 clinical features (contagions, hospitalizations, and deaths) and the extension of public green areas, as well as the annual average concentrations of PM2.5 (with this latter variable loosing statistical significance in some province). Therefore, the extension of public green areas and air pollution seem to have a high correlation with COVID-19 severity.