Is there a very simple (and well-known) way to prevent Covid from continuing its run, a way that puts those who work or study indoors and often without the possibility of choosing not to have close contact with others in safety? It has been talked about from the initial stages of the pandemic, and now the theme of ventilation of the environments in which the virus is stationed more frequently is back, precisely because they are often crowded. It is a research published by The BMJ Journals to face the challenge again.
The new review highlights the importance of adequate ventilation to prevent the spread of Covid indoors. And so it adds further weight to the evidence of “long-distance” airborne transmission of the virus indoors, see restaurants, workplaces and public transport.
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Ventilation restrains the virus
The starting point is an assumption that has already been verified in the recent past: some public places may need better ventilation to prevent the spread of Covid, a need even more evident, the research suggests, following the demonstration of the potential for airborne transmission “a long distance “of the disease.
It is now a review of 18 studies indicating that airborne transmission of SARS-CoV-2 from one infected person to others located more than two meters away may occur in a variety of indoor, even non-healthcare settings. However, the researchers stress that studies on the long-distance potential for airborne transmission of the virus need to be continuously investigated in order to increase the degree of certainty.
The airborne spread of the infection
Since the onset of pandemics and so-called “superspreader” events, there has been mounting evidence to suggest that airborne transmission of the virus in poorly ventilated locations has helped spread the infection.
Superspreader events are those in which an infectious disease spreads far more than usual, while an unusually contagious organism infected with a disease is known as a superspreader. In the case of a human-transmitted virus, a super diffuser is an individual who is more likely to infect others than a typical infected person.
That said, while it is commonly accepted that short-range transmission (less than two meters away) can occur through droplets and aerosols in the air, there is no agreement on the importance of long-distance aerial transmission (for more than two meters) indoors. For example hospitality places, leisure facilities, workplaces or condominiums.
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The review of studies
This is exactly what the team of researchers from the UK Health Security Agency and the University of Bristol thought of, deciding to evaluate the long-distance air transmission potential of Covid in indoor community contexts and to investigate the factors that could influence transmission.
In this regard, research on the subject published between January 2020 and January 2022 was examined, and we focused in particular on 18 observational studies of Covid outbreaks in Asia, Europe, Oceania and the United States.
These are outbreaks that have erupted within various community settings: apartments in condominiums, quarantine hotels, restaurants, buses, a food processing factory, a courtroom, a gym and during singing events.
The conclusions
And here are the conclusions: Long-distance airborne transmission probably occurred for some, or all of the transmission events, in 16 of the 18 studies. Furthermore, in the latter, some factors would have been to increase long-distance contagion, in particularly insufficient air replacement, directional airflow, and activities associated with increased aerosol output, such as singing or speaking loudly.
It should also be noted that in 13 cases examined, people likely to be the source of infection were reported as asymptomatic, presymptomatic, or to the point of just starting to have symptoms at the time of transmission.
“This systematic review demonstrates that long-distance airborne transmission of Covid can occur indoors, such as restaurants and workplaces – explain the researchers -, while factors identified as insufficient air replacement can contribute to the spread of the infection. Hence, these findings support the role of indoor mitigation measures, such as adequate ventilation. “
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“Open air” project
Precisely on this trend he had already moved, in recent months, Roberto Buzzetti, epidemiologist from Bergamo and specialist in medical statistics. “The basic idea of the project was born looking at the typical environment in which several people, gathered indoors, risked contagion – he recalls -. I mean the school. So the bet was that of an open-air school, able to translate into a sharp decline in respiratory pathology among the boys. But the scheme can also be applied in other areas: restaurants, offices, meeting rooms, assemblies ”.
Thinking about this, Buzzetti focused on “rooms equipped with air exchange systems”. Specifying: “There are specific technological solutions. And the costs could be acceptable in a short time, given the possibility of renting the plants in question “.
Air purification systems
Basically they are purifiers. But how to choose them? In order to obtain a satisfactory air exchange, first of all you need to calculate the volume of the room in which to install it and multiply it by the desired number of ACH (Air Changes per Hour). A reasonable number is 4, but in hospital premises, for example, you need to get to 12ACH.
Once this number has been obtained, that is the necessary flow rate, it is necessary to look for a purifier that has a HEPA filter. By definition this filter must be able to remove 99.97% of particles with a diameter of 0.3um, while for those of different diameters the degree of removal is higher. In other words, the performance for that diameter is the minimum of the filter.