Air quality and COVID-19: Much more than six feet. Evidence about SARS-COV-2 airborne transmission in indoor environments and polluted areas

In March 2020, while Italy was the first European country to experience the COVID-19 pandemic, the Italian Society of Environmental Medicine (SIMA) called for carefully considering the role of air pollution in boosting SARS-CoV-2 diffusion, as well as COVID-19 lethality in Lombardy and the neighborhood Northern Italian Regions (Setti et al., 2020a). After displaying the first evidence of SARS-CoV-2 RNA found on particulate matter of Bergamo before the first Italian lockdown (Setti et al., 2020b), the same researchers argued that the simple prescription of maintaining a social distancing of 6 feet (2 m) could not be enough to protect people from contagion, especially in enclosed spaces (Setti et al., 2020c). At that time, the use of facial masks in indoor or outdoor environments was not yet recommended by the World Health Organization, as well as by many Governments. As highlighted by Morawska and Cao (2020) and also by Paules et al. (2020), small particles with a higher viral load, could probably be transferred up to 10 m from the emission source in indoor environments, thus meaning more than 6 feet (2 m). Only in May 2021, due to the increasing evidence produced in medical literature (Domingo et al., 2020; Wu et al., 2020), the Centre for Diseases Control and Prevention (CDC, 2021) updated their official documents concerning the transmission of coronavirus SARS-CoV-2, recognizing that “once infectious droplets and particles are exhaled, they move outward from the source”, and that the transmission of SARS-CoV-2 might occur also at distances greater than six feet (2 m) from the infectious source. This despite being less likely than at closer distances, with the warning that “the progressive loss of viral viability and infectiousness over time is also influenced by environmental factors such as temperature, humidity, and ultraviolet radiation such as sunlight” (CDC, 2021).