If the birth of modern medicine has to be placed at a historical moment, it could have been in the second half of the 19th century when Louis Pasteur demonstrated the germ theory. Infections were not transmitted by miasms unbalancing the mysterious humors, as has been believed since Hippocrates, but by microorganisms present in water, in food, on our own hands, which had hitherto gone unnoticed. The revolution that followed the germ theory also had a side effect: it practically demoted airborne pathogen transmission to the status of superstition. Although other diseases such as tuberculosis and measles have been suspected in the past, the dogma has been that other respiratory infections are not aerosol transmitted. Until the Covid, which, after much controversy, recalled that these diseases can also be in the air.
This development, and public health officials’ reluctance to accept the airborne spread of the coronavirus, is discussed in detail by José Luis Jiménez, Professor of Environmental Sciences and Chemistry at the University of Colorado. He was among the first scientists to warn the World Health Organization about airborne transmission of SARS-CoV-2 and has become an activist calling for action to clean the air we breathe. The recommendation to ventilate indoors, repeated over and over again by experts during the pandemic, seems at odds with the need for energy savings in cold months that coincide with a fossil fuel crisis.
It really doesn’t have to be a contradiction. Modern building codes dictate air renewal practices with low temperature loss. They are dual flow heat recovery systems that use the used exhaust air to heat the clean outdoor air in winter and do the opposite in summer. It is the mechanism used by houses with the highest energy rating, known as Passivhaus (from German, Passivhaus), a private certification that certifies their minimal cost. Spanish regulations have a lower level of requirements for ordinary households, but this type of air renewal is mandatory in buildings and public places built after 2007.
It is set by the regulation on heating systems in buildings, which sets maximum values for the concentration of CO2 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 centres. The problem is that most buildings before this date do not meet these requirements and usually do not comply with this measure. Belén Zalba, an expert in air conditioning from the University of Zaragoza, explains that for years the tightness of buildings has been increased significantly to save energy and prevent uncontrolled air intakes, but not enough progress has been made on controlled air intakes (mechanical ventilation). . “The so-called sick building syndrome developed, although the buildings do not get sick, the residents do get sick,” he says.
Zalba often checks this with its CO2 meter. “The limit is between 800 and 1,000 ppm and I’ve measured more than 2,000, which means I’m breathing the air that other people have been breathing and therefore at risk of disease transmission,” he claims. Zalba is less worried about private households because, despite the urgent recommendation, ventilation is not enough to avoid infection when living together so closely. This changes when visiting people or on dates like Christmas, when houses become festivals and can be a source of the spread of pathogens.
But what really worries Zalba are buildings like nursing homes, which very often don’t meet the above pollution standards and are occupied by elderly people who are most vulnerable to respiratory infections.
In addition to the Covid, there is strong evidence that the air is a vehicle for transmission of others, such as influenza, measles or chickenpox. “And there are many others for which too many experiments have not been conducted due to the traditional assumption that they were transmitted through contact with infected surfaces. “But other coronaviruses such as the common cold or respiratory syncytial virus (which causes bronchiolitis in children) and another range of pathogens are also exhaled in aerosols, as is SARS-CoV-2, so it is logical to assume that it is also spread by them become air,” stresses Jiménez.
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 float in the air for hours. These include anthrax, aspergillosis, blastomycosis, chickenpox, rotavirus, influenza, rhinovirus, meningitis, streptococcus, pneumonia, legionellosis, measles, mumps, tuberculosis, Covid, SARS and MERS.
“Jiménez agrees with other scientists who believe that health authorities have not sufficiently emphasized the importance of clean air because it would mean that the responsibility for regulation would be handed more tightly to them. “There is still an insistence on washing hands because it depends on everyone. If you don’t wash them and get infected, it’s 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 is responsible,” he says.
Although taking action on this matter can mean a heavy investment when adding the adequacy of all buildings, the cost is much less than treating all respiratory infections, says Lidia Morawska, director of the International Air Quality and Health Laboratory. “The cost to society of prevention through better designed buildings and incremental improvements in ventilation in existing buildings is much less than the cost of infection. According to some estimates, this would only represent 1% of the initial construction costs,” he argues.
The necessary equipment depends on the size of the rooms and their use. There are four factors that critically affect the likelihood of transmission of Covid and other airborne infections: the size of the enclosure (which determines how much air is shared), the number of individuals who fall in, the time they spend in it, and the degree of vocalization that occurs. In other words, in a place where people are quiet, such as a cinema, there is not the same risk as in another place where they speak or, even more so, where they sing or shout, in moments when there is more noise, the virus is expelled.
The plants must have an air renewal capacity according to these four conditions. In a place with sufficient infrastructure, it would not be necessary to open windows for ventilation. “Actually, it’s counterproductive because of the energy efficiency and because it interferes with what’s already there,” explains Zalba. A recent study in Italian schools examined 10,000 classrooms, a third of which had a mechanical ventilation system. In them, the risk of Covid infection for students fell by at least 74% compared to classes that only had natural ventilation.
Another alternative that Jiménez points out, which is simpler and cheaper than installing a complete air conditioning system that renews the air, is cleaning. This can be done using air purifiers with HEPA filters, which have been shown to drastically reduce the viral load of shared air in the event of an infected person. And a third would be chemical disinfection, although in most cases this is discouraged as the health risks can outweigh the benefits.
All of these methods do not guarantee that infection will be avoided. It’s a matter of probabilities and what you do by cleaning the air is to reduce them. Experts in this field cite tobacco as an example: if many people smoke in a room, the air is polluted with smoke. If it is not renewed, those sharing the space will inhale it in large quantities. Let’s imagine that this air is populated with viruses instead of smoke. The more inspired they are, the more likely they are to get sick. And the easiest way to determine how polluted the air is today is based on the amount of CO2 present. “The solution is to measure, measure and act on the basis of the measured values,” says Belén Zalba.
To raise awareness of the importance of clean air, the researchers also draw on an analogy with water: Developed countries have made efforts to bring it sanitized into homes, and nobody thinks of drinking it if it’s of dubious origin , a precaution that is not normally taken with what we breathe. “Every day, people breathe in 8,000 liters of air, 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 major impact on our health,” read the conclusions of the last International Congress on Indoor Air Quality, held in Madrid in November, which sets further requirements for the ventilation of public spaces. “Energy saving need not be incompatible with good indoor air quality, as long as the appropriate techniques are applied in the sizing, maintenance and operation of air conditioning systems,” he concludes.