There is an increasing number of epidemiological studies on the transmission of SARS-CoV-2. As time passes, an ever-growing number of scientific publications confirm what was already suspected: the main vehicle in indoor environments are HVAC systems.
This is confirmed by a very recent study about to be published: Lu J, Gu J, Li K, Xu C, Su W, Lai Z, et al. COVID-19 outbreak associated with air conditioning in restaurant, Guangzhou, China, 2020. Emerg Infect Dis. 2020 Jul [date cited]. https://doi.org/10.3201/eid2607.200764, also accessible from the US CDC portal at this link. It was demonstrated that respiratory water vapour (micro-droplets under 5 microns) of a person infected with coronavirus inside a restaurant remained suspended in the flow generated by the air conditioning system, going well beyond the normal recommended safe distance and directly reaching the other diners, who then went on to develop symptoms.
This aspect is fundamentally important and should not be underestimated – we have already discussed it extensively in articles on our website – especially in this delicate phase of resumption of activities.
The key principle to keep in mind is that every sanitisation and disinfection activity, whether of the environment or surfaces, must always be preceded by proper cleaning using appropriate methods. According to this principle, all HVAC systems must also always be cleaned before proceeding with disinfection of the systems themselves, as well as of the environments in which they operate.