Scientists warn of "overwhelming" evidence of airborne coronavirus contagion

For the first time since March, New York allows the use of the interior of its restaurants, like the one in the image, at 25% capacity.Mary Altaffer / AP

While scientists warn that the risk of catching COVID indoors could be almost twenty times higher than outdoors, the authorities continue to reduce the capacity of closed premises and terraces in the same proportion, as if the danger were the same.

They close parks, they open bars.

These examples serve to illustrate the impact of a letter just published in the journal

, in which a group of scientists and doctors explains the importance of taking measures to combat airborne infections.

That is, fitting masks and improving ventilation to prevent someone from breathing and becoming infected with the contagious particles that accumulate suspended when the air is not flowing.

In addition, and around the same time, the US Centers for Disease Control and Prevention (CDC) have updated their guidelines to finally recognize the role that airborne contagion plays.

"There is overwhelming evidence that inhalation of SARS-CoV-2 represents an important transmission route for covid-19," write the letter's authors, led by Kimberly Prather of the University of California, San Diego.

As explained in the article, people with covid, also those who do not have symptoms, release thousands of aerosols loaded with viruses, and also a few droplets, when they breathe, cough, speak or sing.

"Therefore, one is much more likely to inhale aerosols than a drop, so the focus should be on protection against airborne transmission," they say.

For this reason, they demand that the health authorities, together with the known obligations of distance, hygiene and masks, be added new ones specifically focused on avoiding the risk of these aerosols.

"We urge public health officials to add clear instructions on the importance of moving activities outdoors, improving indoor air through ventilation and filtration, and improving protection for high-risk workers," they conclude in their text.

Imagine that other people expel contagious smoke from their mouths, aerosol experts suggest, because that is how these particles behave.

"The masks at all times indoors"

"This virus is released in aerosols that stay afloat in the air, travel more than six feet [two meters] and can accumulate in the air in the room," summarizes Prather in an email.

And she warns: “Masks should be used indoors at all times when there are other people present;

aerosols don't stop at two meters ”.

“The truth is that many authorities include the idea of ​​ventilating interiors in their recommendations.

But since the reason is not explained, much less is fulfilled, ”criticizes aerosol specialist José Luis Jiménez, from the University of Colorado.

Practically all organisms advise it, but in most cases not with the emphasis that this group of scientists claims.

Last week, the director of the Center for Health Alerts and Emergencies, Fernando Simón, assured that we do not have "solid evidence" of transmission by aerosols, although he recognized that "some study appears that seems to indicate this line."

For the most part, official guides assume the existence of three routes of contagion, although not with the same importance.

The droplets that a patient expels and end up in the mouth, eyes or nose of another person (hence the need for distances and masks), the contact of these mucous membranes with some contaminated surface (or fomites, and hence hand hygiene) and inhalation of aerosols.

Floating in the air at five meters

The evidence of the existence of this mode of contagion by breathing microscopic airborne particles has been growing in weight and in support since in February some specialists began to warn of this possibility.

The evidence goes in two directions.

On the one hand, by locating contagious particles, with a sufficient viral load, floating in the air almost five meters from the patient.

On the other hand, the numerous cases of massive infections that are registered week by week and in which only aerosols can explain such a massive infection.

"The evidence from the study of outbreaks, especially massive ones, indicates that in them the contagion has had to be produced mainly by airborne transmission of aerosols, persisting suspended in the air and distributed throughout a poorly ventilated interior room", assures virologist Margarita del Val, director of the CSIC Global Health research group on coronavirus.

For example, the Skagit choir, where one of the singers infected 52 people in a single rehearsal, some located several meters behind him in an unventilated room.

Or the Zumba class from South Korea.

Or the Guangzhou restaurant, in which diners more than four meters from patient zero were infected, with whom they shared a room without external ventilation for an hour.

Despite how extremely difficult it is to know in detail how a person has been infected, there are circumstances that make certain routes ruled out.

“Super-spread events can only be explained by aerosols: everyone breathes the same air in a closed room with little ventilation," says Prather. He adds: "The challenge with this virus is that many people move infected without knowing that they are sick; they exhale infectious aerosols simply by talking. ”Del Val believes that there is less evidence of outbreaks of transmission by surfaces, or by droplets received directly:“ Also admitting transmission by aerosols, without forgetting that both routes can be important in contagion, allows us to react on time and not delay the implementation of measures that would reduce infections in closed places ”.

Even so, the World Health Organization (WHO) only recognized that this airway could play some role in the pandemic after more than two hundred scientists published an open letter demanding that their data be taken into account.

But it only admits it as a possibility, although its guides do encourage improving the ventilation of spaces.

The CDC added more confusion after publishing on its website that inhalation of aerosols was the main route of infection for a couple of days, then completely erased it, claiming that a draft was published by mistake.

Precisely this Monday, the CDC has again updated its guidelines, recognizing that “under certain conditions, people with COVID-19 appear to have infected others who were more than six feet [two meters] away.

These transmissions occurred within enclosed spaces that had inadequate ventilation.

Sometimes the infected person breathed heavily, for example, while singing or exercising. "The Johns Hopkins University, one of the most prestigious in medical matters, considers the role of aerosols evident and points to indoor ventilation as one of the main challenges of this phase of the pandemic.

Closed parks and open bars: “It's the other way around”

This controversy has real effects, it is not purely technical.

The general ignorance of this route of contagion means that, for example, the possibility that the climate of Spain provided to transfer activities abroad has hardly been taken advantage of.

Or that it is decided to reduce the capacity to 50% both in outdoor terraces and inside the premises, when the risk of contagion is much greater inside, while pedestrianized streets and parks are closed.

"It's the other way around," criticizes Prather, "the exterior is better than the interior, due to dilution."

"Bars are the most risky activity: talking loudly, without masks while drinking or eating, poor ventilation, sitting close to each other ... Everything leads to the accumulation of aerosols," explains the scientist.

The University of California professor gives New York City as an example, where all the bars and restaurants closed and the dining rooms have just reopened with only 25% occupancy.

"As schools and businesses open, it is essential that they have the proper guidance to do so safely," she remarks.

Del Val proposes other measures: “How to be more strict recommending masks in all interiors, put the heated air in buildings with central air heating systems in a renewal position, instead of recirculating the air, and study the possibility of equipping them with adequate filters or virus inactivation processes, or even recommend regulated ventilation at various intervals ”.

What is technical is the origin of this controversy, as seen by the signers of this

letter

.

They explain that the droplets that are thrown like projectiles and fall to the ground before crossing the two meter limit are larger (100 microns) and scarcer than was thought when the distinction between droplets and aerosols was established (at 5 microns) , many decades ago.

"Aerosols extend down to 100 microns, not the old 5 micron belief, established by the WHO," Prahet explains.

This justifies a large part of the resistance, because it would force a review of many criteria on which many health workers have been educated for decades.

For this reason, in this controversy, there has sometimes been a confrontation between specialists in aerosols, from disciplines such as Physics, with biosanitary with more experience in contagion, but less in how fluids behave in the air.

The

letter is

signed by two aerosol experts, but also by doctors, virologists, and public health specialists.

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