“Current evidence suggests that COVID-19 spreads between people through direct, indirect (through contaminated objects or surfaces), or close contact with infected people via mouth and nose secretions. These include saliva, respiratory secretions or secretion droplets. These are released from the mouth or nose when an infected person coughs, sneezes, speaks or sings, for example. […]. To avoid contact with these droplets, it is important to stay at least 1 meter away from others, clean hands frequently, and cover the mouth […] when sneezing or coughing. Physical distancing, wearing mask, (WHO, 2020) quarantine and contact tracing is important to protect others and a good opportunity to stop COVID-19 pandemic (Zhang et al., 2020).
Not only physical contact with an infected person or through touching a contaminated surface can lead to a COVID-19 infection but also the inhalation of small COVID-19 contaminated droplets (called aerosolized droplet nuclei or aerosols) (Bounanno et al., 2020, WHO, 2020, Zhang et al., 2020). Zhang et al., revealed in their scientific paper, that “[…] airborne transmission is highly virulent and represents the dominant route to spread the disease” (Zhand et al., 2020). Outbreaks of COVID-19 through aerosol transmission have been reported from “indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods of time with others” (WHO, 2020). The importance of the transmission by aerosols has also been studied previosuly on other interhuman respiratory viruses including influenza virus, SARS-CoV-1 (coronavirus responsible for the 2002-2003 SARS outbreak), and the Middle East Respiratory Syndrome coronavirus (MERS-CoV, (Zhang et al., 2020)). “While transmission via direct or indirect contact occurs in a short range, airborne transmission via aerosols can occur over an extended distance and time. Inhaled virus-bearing aerosols deposit directly along the human respiratory tract” (Zhang et al., 2020). “Recent experimental studies have examined the stability of SARS-CoV-2, showing that the virus remains infectious in aerosols for hours” (Zhang et al., 2020)- for at least three hours according to Bounanno et al. (2020).
“Within an enclosed environment, virus-bearing aerosols from human atomization are readily accumulated, and elevated levels of airborne viruses facilitate transmission from person to person” (Zhang et al., 2020). “Even with normal nasal breathing, inhalation of virus-bearing aerosols results in deep and continuous deposition into the human respiratory tract, and this transmission route typically requires a low dose. Also, airborne viruses have great mobility and sufficiently long surviving time for dispersion, and residents situated in densely populated environments are highly vulnerable. In addition, nascent micrometer-size aerosols produced from coughing/sneezing of infected people have the potential of containing many viruses, particularly from asymptomatic carriers (Zhang et al., 2020).
Given the rapid spread of the disease, including through asymptomatic carriers, it is of clear importance to explore practical mitigation technologies that can inactivate the airborne virus in public locations, especially when people are around, and thus limit airborne transmission (Buonanno et al., 2020; Brenner, 2020; Welch, 2020).