Two mechanisms for accelerated diffusion of COVID-19 outbreaks in regions with high intensity of population and polluting industrialization: the air pollution-to-human and human-to-human transmission dynamics

Mario Coccia

of asthma or asthma-like symptoms (Shankardass et al., 2009; Weinmayr et al., 2010) . Especially, current evidence indicates that PM10 increases cough, lower respiratory symptoms and lower peak expiratory flow (Ward and Ayres, 2004; Nel, 2005) . Weinmayr et al. (2010) provide strong evidence that PM10 may be an aggravating factor of asthma in children. Furthermore, asthma symptoms are exacerbated by air pollutants, such as diesel exhaust, PM10, NO2, SO2, and O3 and respiratory virus, such as adenovirus, influenza, parainfluenza and respiratory syncytial virus (Jaspers et al., 2005; Murdoch and Jennings, 2009; Murphy et al., 2000; Wong et al., 2009) . The study by Liao et al. (2011) confirms that exacerbations of asthma have been associated with bacterial and viral respiratory tract infections and air pollution. Some studies have focused on the effect of meteorology and air pollution on acute viral respiratory infections and viral bronchiolitis (a disease linked to seasonal changes in respiratory viruses) in the first years of life (Nenna et al., 2017; Ségala et al., 2008; Vandini et al., 2013 Vandini et al., , 2015 . Carugno et al. (2018) analyze respiratory syncytial virus (RSV), the primary cause of acute lower respiratory infections in children: bronchiolitis. Results suggest that seasonal weather conditions and concentration of air pollutants seem to influence RSV-related bronchiolitis epidemics in Italian urban areas. In fact, airborne particulate matter (PM) may influence the children's immune system and foster the spread of RSV infection. This study also shows a correlation between short-and medium-term PM10 exposures and increased risk of hospitalization due to RSV bronchiolitis among infants. In short, manifold environmental factorssuch as air pollution levels, circulation of respiratory viruses and colder temperaturesinduce in longer periods of time spent indoors with higher opportunities for diffusion of infections between people. In fact, in Italy the high diffusion of viral infectivity by COVID-19 in North of Italy is in winter period (February-March, 2020). Studies also show that air pollution is higher during winter months and it has been associated with increased hospitalizations for respiratory diseases (Ko et al., 2007a; Medina-Ramón et al., 2006) . Moreover, oscillations in temperature and humidity may lead to changes in the respiratory epithelium which increased susceptibility to infection (Deal et al., 1980) . Murdoch and Jennings (2009) correlate the incidence rate of invasive pneumococcal disease (IPD) with fluctuations in respiratory virus activity and environmental factors in New Zealand, showing how . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.