The update came a few weeks after WHO acknowledged the possibility of airborne transmission, especially in crowded, poorly-ventilated spaces, thanks to the intense advocacy by scientists around the globe, including several REHVA experts. Without doubt, ventilation is the most important engineering control measure within infection control of indoor spaces.
New evidence and the general recognition of the aerosol-based transmission route have evolved recently. To date, there is evidence on SARS-CoV-2 aerosol-based transmission, and this route is now recognised worldwide. Transmission routes remain an important research subject, and it has already been reported that the short-range aerosol-based route dominates exposure to respiratory infection during close contact1.
Medical literature has started to talk about a new paradigm of infectious aerosols and there is no evidence to support the concept that most respiratory infections are primarily associated with large-droplet transmission. It seems that small particle aerosols are the rule, rather than the exception, contrary to current guidelines. In the context of buildings and indoor spaces there is no doubt that cross-infection risk may be controlled up to 1.5m from a person with physical distancing and beyond that distance distribution solutions. See Figure 1.
Key aspects to consider In such a pandemic situation at least three levels of guidance are required: (1) how to operate HVAC and other building services in existing buildings right now; (2) how to conduct a risk assessment and assess the safety of different buildings and rooms; and (3) what would be more far-reaching actions to further reduce the spread of viral diseases in future in buildings with improved ventilation systems.
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