While governments around the world recommend taking all activities outside and airing indoors, an intense scientific debate remains open about the reasons for doing so. No health agency denies that there are infections by air, that is, by breathing in particles with viruses that remain in suspension after being expelled by an infected person when talking, screaming or coughing. This type of contagion is what would justify these measures, which is now recommended by the World Health Organization (WHO), although initially it discussed the existence of infections by aerosols, those viral particles in suspension. But the controversy remains because a virus has not yet been caught in the air that infects someone and many specialists argue that the main route of infection are droplets that impact like pellets in direct contact with a patient.
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A team of scientists, including the Spanish José Luis Jiménez (University of Colorado), publish now in The Lancet a compilation of the ten scientific arguments that support the existence of aerosols as a major player in the covid pandemic. Already in March 2020 they demanded that the WHO take into account this air hazard, but now the evidence is accumulating. His argument begins by acknowledging its main weakness, published by another specialist: “The lack of recoverable samples of viral cultures of SARS-CoV-2 prevents firm conclusions on airborne transmission.” For these scientists, from universities such as Oxford, California and Toronto, this conclusion “is worrying due to the implications for public health”: it is not the same to fight a few drops that fall to the ground than an invisible nebula that remains in suspension. And then they detail their reasons, reviewed by other independent scientists for the prestigious journal.
1- Events of super spread. These situations, in which many people are infected in the same setting, are considered one of the main drivers of the pandemic. The analysis of massive contagions in choirs, cruise ships, restaurants, slaughterhouses, homes for the elderly and prison facilities suggests that the airway plays a determining role in these cases, “which cannot be adequately explained by droplets or fomites. [superficies contaminadas]”, According to this group.
2- Contagion of long-range. New Zealand has documented a contagion between two people who did not even cross, caused by poor ventilation in a hotel with people in quarantine.
3- Transmission asymptomatic or presymptomatic. The determining role played by symptom-free contagion supports “a predominantly airborne mode of transmission,” according to these scientists, because “direct measurements show that talking produces thousands of aerosol particles and few large droplets.”
New Zealand has documented a contagion between two people who did not even cross, caused by poor ventilation in a hotel
4- Interiors. Since the beginning of the pandemic, it has been known that indoors places are about twenty times more likely to cause infections than outdoors. And that the risk is remarkably reduced with indoor ventilation, which suggests the existence of an airborne transmission route, which dissolves with circulating air.
5- Infections in hospitals. Infections in medical centers, where strict precautions are applied against direct contact and large droplets, but not so much against contagion by microscopic particles in suspension that can be inhaled.
6- It has been detected in the air. In experiments it has been possible to determine that SARS-CoV-2 remained infectious in the air up to three hours and five meters from a patient, but there are other studies that have failed to capture aerial samples that can be cultured, that is, that show the ability to infect. This is one of the main keys that raises doubts: the absence of solid evidence of viruses that spread in the air. The signatories of the article in Lancet They argue that airborne virus sampling is a technical challenge and give an example: “Measles and tuberculosis, two primarily airborne diseases, have never been cultivated from ambient air.”
7- Traces in air filters. Scientists have found traces of the coronavirus in air conditioning systems and building ducts, “places that could only be reached by aerosols.” Furthermore, the use of these traces of coronavirus in air filters as an alert system for the presence of infections in an area is being investigated.
8- Caged animals. Several studies have tested infections between ferrets and other animals that they were in separate cages and that can only be explained by airborne transmission.
9- Evidence against. The signatories of the article admit here another Achilles heel: that many people do not become infected after sharing air with infected people as it happens with other more contagious diseases through the air, such as measles. “This situation could be explained by a combination of factors”, they are justified, and point out the different viral load of individuals and environmental conditions.
10- Other routes of transmission. This group points out that there is more limited evidence on the other two possible routes of infection: respiratory droplets and contact with surfaces (fomites). All health agencies now recognize that the latter, touching contaminated objects, is rare if not very unlikely. The droplets would explain better with contagions by proximity, but these could also be explained by aerosols, since they are concentrated in greater quantity near the person who expels them.
Covid has redefined airborne transmission
This heading is the title of an opinion article that another group of scientists, from universities such as Leicester or Virginia Tech, publish in the magazine British Medical Journal , one of the most important in the sector. In their article, they once again insist on the need for authorities to focus their attention on airborne infections, recognizing that a redefinition of these classic medical terms is needed because of the false distinction between “droplets” and “airway” generates confusion when it comes to infectious particles of many sizes that may or may not remain in suspension and infect. And they add: “This does not mean that the transmission does not occur through contact with surfaces or by air of greater range, but they are less important than those that happen during brief daily interactions in the usual conversation distance of one meter.”
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