If the birth of modern medicine has to be located at a moment in history, it could be in the second half of the 19th century, when Louis Pasteur demonstrated the germ theory. Infections were not transmitted by miasmas that unbalanced the mysterious humors, as had been believed since the time of Hippocrates, but by microorganisms present in water, in food, on our own hands, and which had gone unnoticed until then. The revolution that followed the germ theory also had a side effect: it virtually relegated the airborne transmission of pathogens to the status of superstition. Although it was assumed in the past with other ailments, such as tuberculosis and measles, the dogma was maintained that other respiratory infections were not spread by aerosols. Until the covid that, after much controversy, came to remember that these diseases can also be in the air.
This evolution and the resistance of the health authorities to accept that the coronavirus is spread through the air is dealt with at length by José Luis Jiménez, professor of Environmental Sciences and Chemistry at the University of Colorado. He is among the first scientists to warn the World Health Organization about the airborne transmission of SARS-CoV-2 and has become an activist calling for measures to clean up the air we breathe. The recommendation to ventilate indoors, repeatedly repeated by experts during the pandemic, seems to conflict with the energy savings needed in cold months that coincide with a fossil fuel crisis.
It really wouldn’t have to be contradictory. Modern building codes mandate air renewal procedures with little loss of temperature. They are double flow systems with heat recovery that, in winter, take advantage of the stale air that comes out to heat the clean air that comes in from outside and in summer they do the opposite. It is the mechanism used by homes with the highest energy rating, known as passivhaus (from German, passive house), a private certification that accredits its minimum expense. Spanish regulations have a lower level of requirements for common households, but this type of air renewal is mandatory in buildings and public places built after 2007.
It is established by the Regulation for Thermal Installations in Buildings, which provides maximum CO2 concentration values in these rooms: an ideal of 350 parts per million (ppm) above the concentration in the outside air, which applies in venues such as hospitals or day care centers. The problem is that the buildings prior to this date, which are the majority, do not have these requirements, and do not usually comply with this measure. Belén Zalba, an expert air conditioning engineer from the University of Zaragoza, explains that for years the tightness of buildings has been significantly increased to save energy to prevent uncontrolled air inlets, but not enough progress has been made in controlled air inlets (mechanic ventilation). “It gave rise to what is known as the sick building syndrome, although the buildings do not get sick, the occupants get sick,” she says.
Zalba often checks this with his CO2 meter. “The limit is between 800 and 1,000 ppm and I have measured more than 2,000, which means that I am breathing the air that other people have breathed and, therefore, there is a risk of disease transmission”, he maintains. Zalba is not so concerned about private homes, since ventilation, despite being highly recommended, is not enough to avoid contagion with such close coexistence. This changes when there are visits or on dates such as Christmas, when houses become venues for celebrations and can be a source of spread of pathogens.
But what really worries Zalba are buildings such as nursing homes, which very often do not meet the aforementioned pollution standards and are inhabited by older people, the most vulnerable to respiratory infections.
In addition to the covid, there is strong evidence that the air is a vehicle for the transmission of others, such as the flu, measles or chickenpox. “And there are many others for which too many experiments have not been done due to the traditional assumption that they were transmitted by contact with infected surfaces. “But other coronaviruses, such as colds, or the respiratory syncytial virus (which causes bronchiolitis in children) and another series of pathogens are exhaled in aerosols just like SARS-CoV-2, so it is logical to assume that they are also spread by air”, Jiménez insists.
Various scientific publications list an extensive catalog of diseases that can be transmitted by aerosols, since their pathogens travel in tiny droplets that do not fall to the ground and can remain suspended in the air for hours. They include anthrax, aspergillosis, blastomycosis, chickenpox, rotavirus, influenza, rhinovirus, meningitis, streptococcus, pneumonia, legionellosis, measles, mumps, tuberculosis, covid, SARS and MERS, among others.
“Jiménez is in line with other scientists who believe that the health authorities have not placed sufficient emphasis on the importance of clean air because that would mean transferring the responsibility of regulating it more demandingly to them. “Hand washing is still insisted on because that is something that depends on each one, if you do not wash them and you get infected, it is your fault. But you can’t help but breathe the polluted air of a place open to the public. If you get infected, the venue has a responsibility, ”he maintains.
Although taking action on this matter can have a high investment if the adequacy of all the buildings is added, the costs are much lower than treating all respiratory infections, says Lidia Morawska, director of the International Laboratory for Air Quality. and health. “The cost to society of prevention through better designed buildings and the gradual improvement of ventilation in existing buildings is much less than that of infections. By some estimates, this would represent only 1% of the initial construction costs,” she argues.
The necessary facilities depend on the size of the rooms and their use. There are four factors that decisively influence the probability of transmission of covid and other airborne infections: the size of the enclosure (which determines how much air is shared), the number of people who coincide, the time they spend in it and the degree of vocalization that occurs. In other words, it is not the same risk in a place where people are quiet, such as a cinema, as in another where they talk or, even more so, where they sing or shout, moments in which a greater amount of noise is expelled. virus.
The systems must have an air renewal capacity in accordance with these four conditions. In a place with adequate infrastructure, it would not be necessary to open windows to ventilate. “In fact, it is counterproductive, due to energy efficiency and because it interferes with what is already there,” explains Zalba. In a recent investigation in Italian schools, 10,000 classrooms were studied, of which a third had a mechanical ventilation system. In them, the risk of covid infection for students dropped by at least 74% compared to classes that only had natural ventilation.
Another alternative that Jiménez points out, simpler and cheaper than installing an entire air conditioning system that renews the air, is to clean it. For that, purifiers with HEPA filters can be used, which have been shown to drastically reduce the viral load of the air that is shared in case there is an infected person. And a third would be to disinfect it with chemical procedures, although it is discouraged in most cases because the health risks may outweigh the benefits.
All these methods do not guarantee that contagion will be avoided. It is a question of probabilities and what you achieve by cleaning the air is to reduce them. To understand it, experts in this field give the example of tobacco: if there are many people smoking in a room, the air is charged with smoke. If it is not renewed, those who share space will breathe it in large quantities. Let’s imagine that instead of smoke, that air is populating with viruses. The more they are inspired, the more chances there are of getting sick. And the simplest way today to find out how polluted the air is is to check the amount of CO2 there is. “The solution is to measure, measure and act based on the measured values”, says Belén Zalba.
To raise awareness of the importance of clean air, the researchers also resort to an analogy with water: developed countries have been concerned with bringing it disinfected to homes and nobody thinks of drinking it if it is of dubious origin, a precaution that is not usually taken have with what we breathe. “People inhale 8,000 liters of air throughout the day, eat a kilo of food and drink two liters of water. We need to breathe constantly, so the quality of the air we breathe has a great impact on our health”, state the conclusions of the last International Congress on Indoor Air Quality, which was held in November in Madrid, and which calls for more demanding regulations in ventilation of public spaces. “Energy saving does not have to be incompatible with good indoor air quality, as long as the appropriate techniques are used in the dimensioning, maintenance and operation of air conditioning installations”, he concludes.
