In the pre-covid world, air conditioning was the king of summer, now it can be a serious problem: what we know and how to avoid it

On January 24, 2020, ten family members went to a Guangzhou restaurant to celebrate Chinese New Year. It was a nice, modern place. The dining room was about 145 square meters and was located on the third, windowless floor of a building of five. There were 89 people on the premises. It was a good meal except for one small detail.

Between January 26 and February 10, ten of those 89 people developed symptoms of coronavirus pneumonia. When the trackers spoke to all of them they only had one risky contact, a concerned family member who had just arrived from Wuhan a few hours earlier. It was not unusual that they had been in the same closed room for between 53 and 73 minutes at tables that were around a meter away.

But, curiously, they were not the ones who stayed the longest at the venue, nor the ones closest to each other. Why, out of almost a hundred people, only ten became infected? What's more, why only those ten specific people? The answer was much more unexpected than it might seem: the air conditioning was responsible. And that obviously leaves numerous questions on the table. As deconfusion progresses and heat reaches the northern hemisphere, what do we know about weatherization and the coronavirus?

The 'time bomb' that can be hidden in air conditioners

Rene Deanda

There has been a lot of talk in recent weeks about "super scattering events." That is to say, the fact that, unlike other infectious diseases, with the coronavirus the vast majority of those infected do not transmit the virus and only a few infected people end up infecting a large number of people. Current estimates say that 10% of those infected originate 80% of transmissions.

As of today we do not know if these "super dispersers" have common genetic, immunological or social characteristics. However, we do have evidence that massive infections occur in situations with similar circumstances: "when there are infected people in closed spaces and in continuous contact with other people." If we look at the most extensive studies, we see that "most of the clusters originated in gyms, pubs, live music venues, karaoke rooms and similar establishments where people gather, eat and drink, chat, sing, they exercise or dance, rubbing their shoulders for relatively long periods of time "

In a world conquered by air conditioning, common sense tells us that the confluence between unconfinement and the arrival of summer in the northern hemisphere can generate many cases in which infected people spend long periods of time "in closed spaces and in contact I continue with other people. " Even more so if, as it seems with the example of the Guangzhou restaurant, the air conditioning systems turn out to be unexpected allies of the SARS-CoV-2.

What we know about how the virus is transmitted

United Nations Covid 19 Response

In fact, it is not the only documented case in which air conditioning systems appear to have played a role in facilitating outbreaks. However, although the researchers are working at full speed, we are still not sure how and why that amplifying effect occurs. Given this, we are left to resort to what we do know about the transmission of the SARS-CoV-2.

In general terms, there are three fundamental ways to contract it: By direct contact (by touching sensitive areas of an infected patient), by indirect contact (by touching objects contaminated with the virus) and by respiratory flow (through the drops that we expel when cough, sneeze, or talk). There is one more case in which the evidence is less clear: aerosol infection. It is an intermediate situation between the "respiratory flow path" (in the droplets they quickly settle on the ground) and the "airway" (in which the virus is able to live in the air and retain its infective capacity for a long time) weather).

Although, as I say, there is no absolute consensus among researchers, with the available evidence we can assume that this virus does have the ability to be transmitted by aerosols; that is, it can be in the environment for time windows ranging from a few minutes to several hours. The question, however, is not in its theoretical capacity, but in what is its priority path of contagion. That is what depends on whether the effect of the air is simply bad or is very worrying.

What should we do to avoid unnecessary risks?

Mostafa Meraji

If we draw a continuum between the contagion by flow and the contagion by aerosols, the danger of the air will increase as the priority route of contagion of the virus is closer to the latter. With the contagion by flow, the air conditioning machines have as their main problem that they can increase the radius of virus spread; With the spread of aerosols, airs (especially in a closed circuit) could end up considerably increasing the 'viral load' in the environment. The latter would potentially be much more dangerous.

The good news is that cases like the Guangzhou New Year meal seem to hint that the main means of transmission is contagion by respiratory flow: in the restaurant in question all the infected were in the direction of the air conditioning. Just what we would expect to see in the type of contagion: the drops spread further, but quickly landed on the floor, tables or people.

This leads us to believe that simple measures such as preventing air recirculation or using machine filtering can help reduce exposure to the virus. However, it is too early to put all our precautions on those two measures. Therefore, reports from professional organizations (both from the Spanish Society of Environmental Health and the Federation of European Heating, Ventilation and Air Conditioning associations) recommend direct ventilation (through windows) and avoid centralized systems (to avoid possible spread to spread outside the room) to avoid problems. Things like changing the filters or cleaning the ducts are actions that have not been proven effective.

In short, as the virologist and researcher of the Higher Council for Scientific Research Margarita de Val explained to Webedia, it is vital "to promote the outdoors as much as possible. Ventilate indoors and only when it is essential, but really essential, to use air conditioned without recycling, taking air from outside ".

Image | Ashkan Forouzani

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