Humans in the 21st century spend most of their time indoors, but the air we breathe inside buildings is not regulated to the same degree as the food we eat and the water we drink.
A group of 39 researchers from 14 countries, including two from the University of Colorado Boulder, say that needs to change to reduce disease transmission and prevent the next pandemic.
In a Perspectives piece published in Science May 14, they call for a “paradigm shift” in combating airborne pathogens such as SARS-CoV-2, the virus that causes COVID-19, demanding universal recognition that respiratory infections can be prevented by improving indoor ventilation systems.
“Air can contain viruses just as water and surfaces do,” said co-author Shelly Miller, professor of mechanical and environmental engineering. “We need to understand that it’s a problem and that we need to have, in our toolkit, approaches to mitigating risk and reducing the possible exposures that could happen from build-up of viruses in indoor air.”
The paper comes less than two weeks after the World Health Organization (WHO) changed its website to acknowledge that SARS-CoV-2 is spread predominantly through the air, and 10 months after the WHO acknowledged the potential for aerosol transmission and 239 scientists (including Miller and Jose-Luis Jimenez) signed an open letter to medical communities and governing bodies about the potential risk of airborne transmission.
The researchers now call on the WHO and other governing bodies in this new article to extend its indoor air quality guidelines to include airborne pathogens and to recognize the need to control hazards of airborne transmission of respiratory infections.
Such a shift in ventilation standards should be similar in scale to the 19th century transformation that took place when cities started organizing clean water supplies and centralized sewage systems. But it would also correct a major scientific misperception that arose around the same time.
When people in London were dying of cholera in the 1850s, scientists assumed the disease was airborne. But British physician John Snow discovered that microorganisms in contaminated water were the reason. Similarly, Hungarian physician Ignaz Semmelweis showed that handwashing before delivering a baby greatly reduced postpartum infections.
While these discoveries encountered great resistance in their time, scientists eventually agreed that in these cases, water and hands – not air – were the vector for disease.
Then in the early 20th century, American public health expert Charles Chapin erroneously attributed respiratory infections caught in close proximity to other people to large droplets produced by an infected person, which fall quickly to the ground. As a result, he stated that airborne transmission was almost impossible.
Yet in 1945, scientist William Wells published a paper in the predecessor to Science, lamenting that while we were investing in disinfecting water and keeping our food clean, we had done nothing for our indoor air, given the denial of airborne transmission. His research on measles and tuberculosis – caused by airborne pathogens – challenged this notion in the 20th century, but didn’t break it.
Now that the research on SARS-CoV-2 finally has brought to light that many respiratory diseases can be transmitted through the air, researchers argue that we must take action.
“Let’s now not waste time until the next pandemic,” said said co-author Jose-Luis Jimenez, fellow in the Cooperative Institute of Research Sciences (CIRES) and professor of chemistry at CU Boulder. “We need a societal effort. When we design a building, we shouldn’t just put in the minimum amount of ventilation that’s possible, but instead we should keep ongoing respiratory diseases, such as the flu, and future pandemics in mind.”
The long-standing misunderstanding of the importance of airborne transmission of pathogens has left a large gap of information in how to best construct and manage building ventilation systems to mitigate the spread of disease—with the exception of some manufacturing, research and medical facilities.
Instead, buildings have focused on temperature, odor control, energy use and perceived air quality. So while there are safety guidelines for chemicals such as carbon monoxide, there are currently no guidelines, globally or in the U.S., that regulate or provide standards for mitigating bacteria or viruses in indoor air resulting from human activities.
“Air in buildings is shared air—it’s not a private good, it’s a public good. And we need to start treating it like that,” said Miller.
Lidia Morawska, lead author on the article and director of Queensland University of Technology’s International Laboratory for Air Quality and Health, said there needs to be a shift away from the perception that we cannot afford the cost of control.
She notes that the global monthly cost from COVID-19 had been conservatively estimated as $1 trillion and the cost of influenza in the U.S. alone exceeded $11.2 billion annually.
While detailed economic analysis has yet to be done, estimates suggest necessary investments in building systems may be less than 1% of the construction cost of a typical building.
Ventilation systems should also be demand-controlled to adjust for different room occupancies, and differing activities and breathing rates, such as exercising in a gym versus sitting in a movie theatre, according to Morawska. For spaces that cannot improve ventilation to an appropriate level for the use of the space, she said air filtration and disinfection will be needed.
Because buildings consume over one-third of energy globally, much from heating or cooling outdoor air as it is brought indoors, it would be useful to design a “pandemic mode,” that would allow for buildings to only use more energy when necessary, said Jimenez.
The researchers also call for national comprehensive indoor air quality (IAQ) standards to be developed and enforced by all countries, and for this information to be available to the public.
For this to happen, however, many more than scientists will need to understand its importance.
“I think there is a certain amount of demand that needs to start coming from the consumer and from the person who works in these indoor spaces in order to push change,” said Miller.
Unexpected Forms of Transmission and the Role of Policy
The COVID-19 pandemic consistently demonstrated a pattern of growing community transmission worldwide, even with the adoption of social distancing measures (lockdown or voluntarily shelter in place) in January and early May 2020. The continuing transmission of the virus despite the policy measures adopted in some countries was an important point of debate and investigation in the scientific community and among authorities. Unexpected forms of transmission (atmospheric [1-3]) associated with the social distancing policy became the central question for the infectious transmission modeling of SARS-CoV-2 and predictive methods.
This research considers the advanced phases of community transmission observed in some countries  in a select period. Due to the increasing numbers of new infections and deaths, monitored by the World Health Organization  and Johns Hopkins University, this research is mainly focused on the nonlinear epidemic properties of SARS-CoV-2 transmission.
These nonlinear epidemic properties of transmission can be understood through the highly random forms of virus transmission associated with human social behavior and with environmental conditions (physical or aerosol long-range transmission, airborne transmission).
In this research, nonlinearity refers mainly to the unpredictability of the epidemiologic framework of the SIR (susceptible, infected, removed) stochastic models used to track the possible rate of infection in the population, even with some policy measures implemented by countries [5-8].
This limited ability to predict future rates of contagion was noted during the spread of the pandemic. It was suggested that the qualitative theory of differential equations may be appropriate for identifying the variables, policies, or environmental conditions that influence the constant propagation of the virus.
The random patterns of virus reproduction suggest that transmission happens through the air. Other dimensions of research must be considered—the social behavior of individuals and the aerosol fluid dynamic behavior. This direction of research has yielded unresolved mathematical equations that simulate the daily growth of new cases. This study defined the aerosol, or biosol, or ground form of transmission as spreading patterns of infection.
The policy measure adopted by a country may or may not address these spreading patterns adequately, which then may sustain (or not) dissemination patterns of the virus worldwide. In this way, the spreading pattern is related to the forms of virus transmission. At the same time, the dissemination of the virus, regardless of how it can be transmitted, depends on the cultural, personal, and policy aspects of managing societal and individual behaviors.
In this study, geographical regions in Asia, South America, North America, the Middle East, Africa, and Europe were analyzed to confirm whether the policies adopted by China and South Korea during the outbreak were the most effective ones in the period of January to April 2020. During this period, only these two countries had adopted specific policy measures addressing the airborne framework of SARS-CoV-2 transmission beyond social distancing (mask wearing and city disinfection).
These countries also had the lowest daily new case counts of COVID-19. The relationship between mask wearing, city disinfection, and the airborne form of transmission during the period of interest will be used to test the hypothesis that the virus can be transmitted through the air.
Theoretical Analysis of the Nonlinear Properties of SARS-CoV-2 Dissemination Patterns
SARS-CoV-2 follows different patterns of transmission among humans [5-7]. These patterns are being investigated not only using clinical trials, statistical tools [5-11], and medical interviews with patients [9,10], but also from a mathematical point of view, using SIR compartmental models with a high degree of uncertainty. Concerning mathematical predictions of SARS-CoV-2 reproductive patterns within a complex network of human behavior , the maximum possible rate of infection with the virus in daily human life [5-8,12,13] consists of a community dissemination pattern with an increasing margin of statistically unpredictable outcomes.
The models were still being developed due to predictive failures. One specific unpredictable pattern  of the virus spread and dissemination from January to April 2020 is visible in the numbers of new infections over time in countries where the input and output (which is the number of people who could be infected from an initial number, resulting in maximum and minimum margins of dissemination of the virus fluctuation) expressed unpredictability. This observation was initially and briefly modeled by Koerth et al .
Regarding these nonlinear aspects of infection within countries, this study points out that there is evidence for long-range airborne transmission [16-18] of SARS-CoV-2. The evidence consists of the type of policies adopted in China and South Korea from January to April 2020, where a significant reduction in infection cases occurred, with distinct patterns found in other countries during all epidemic contagion phases.
China and South Korea instituted social or physical distancing measures along with additional methods, such as mask use and city disinfection. It was one of the main causes of the nontrivial frequency of daily new COVID-19 case distribution during the early stage of the pandemic, up to late April and early May. Physical distancing with an air preventive framework was revealed to be an urgent need for any country at that time, and, along with social distancing and testing policies, is now one of the main preventive methods used.
Recent studies reported that the transmission of SARS-CoV-2 occurs due to proximity to other humans and to social interactions within a set of empirical variables, including the most basic forms of human behavior, such as coughing, sneezing, handshakes, sharing clothes, sharing cups, general touching, and general object-sharing behaviors [19,20]. This set of variables influences transmission, together with the environmental factors associated with the virus’s possible transmission on the ground (surfaces) and in the air (not only aerosols in medical facilities but aerosol and biosol formed under atmospheric conditions outdoors).
This leads to new patterns for course epidemiology . Between January and April 2020, the World Health Organization confirmed aerosol transmission only at medical facilities , not in outdoor urban spaces. However, van Doremalen et al  stated early on that human upper and lower respiratory tracts cause the nearby atmosphere to become infected, propagating the virus through the air.
They measured this effect for about 3 hours during an experiment and observed low infection reduction over time, with infectious titer changing from 103.5 to 102.7 TCID50 (50% tissue culture infective dose) for SARS-CoV-2 . An alternative scientific hypothesis and further probabilistic and statistical frameworks were needed to establish new policies and guide individual preventive actions.
Although a scientific breakthrough occurred early in the pandemic, no policy measure was announced as definitive, and each country was searching for preventive methods independently. This is why it is worthwhile to compare how some countries reduced SARS-CoV-2 transmission with specific social distancing measures.
The analysis of the nonlinear properties of the mathematical models and nonpharmaceutical interventions for the COVID-19 epidemiological framework is important not only for medical facilities but also for public policies and health care infrastructure.
It can help to estimate the disease patterns of community transmission in a pandemic scenario that affect the economy and threaten people’s health and survival. This research is also relevant due to the large active workforce trying to maintain essential services and sectors necessary for survival, such as electrical, water, garbage disposal, energy, food supply/production, commerce, and industry.
COVID-19 Transmission Instability
Policy that consists of physical distance between individuals may fail because the virus may continue to be transmitted in other unexpected ways. This instability becomes visible when countries that adopt this policy still fail to contain virus spread due to asymptotic instability between the virus’s potential to infect individuals in spite of the policy measures and methodology.
The unbalancing of this equation is found in a wide variety of probability distributions of daily new cases, with distinct patterns [6-9,12,13,15,19,23] observed in many countries . This may be why new cases continued to occur between January and April 2020, even with preventive methods such as social distancing (lockdown or shelter in place) and COVID-19 testing.
Causes beyond the traditional transmission analysis [5-9,13,24-26] need to be considered to explain the continued growth of new cases. Other factors for transmission and modeling patterns should be considered and constructed [12,13,15,27-30] using mathematical counterproof predictions for countries that had already adopted social distancing and had COVID-19 testing available but adopted social physical distancing measures with distinct parameters such as using or not using masks and city disinfection.
Statistical Uncertainty and COVID-19 Prevention
Many variables affect virus transmission rates, such as the type of health policies adopted by each country, public health infrastructure, population genetics, human variance in biological resistance, local epidemic outbreaks, globalization aspects, COVID-19 testing availability, virus mutation, and citizens’ adherence to social physical distancing. The influence of these factors is visible on the Our World in Data webpage .
These confounding outcomes in each country make it difficult to determine why some countries still have an active virus infection and what would be the best fixed-point orientation (policy measure) to reduce virus transmission rates. However, worldwide statistical data can provide a relevant confidence interval analysis if different countries’ policies are compared. This would reveal the best approach for reducing virus infections. At the moment, policy is the most effective way to reduce COVID-19 cases since no vaccine or drugs have been consistently effective for treating the disease or stopping virus propagation worldwide.
Research shows that individual behavior and social ties [32-34] are still key for controlling the community transmission of the virus through social distancing measures. These measures must consider the dynamics of groups/communities and the community infrastructure (households, buses, shopping malls, meetings, markets, daily activities, and human behavior). Note that the term “social distancing” is used here to describe the behavior of an uninfected individual outside medical facilities and refers only to the population separation patterns based on ground distances. The term “social physical distancing” refers to one of the measures included in the social distancing policies.
To explain why the virus continues to be transmitted when social physical distancing is practiced, it is important to consider that social contact might still occur as a human physical connection during environmental socialization; that is, physical ground and atmospheric contact may occur.
The policy requires individuals to stay 1 or 2 m apart, assuming that this is enough to prevent virus transmission, and has the same effect as sheltering in place (mandatory or not). However, with this measure, there are still many opportunities for social contact within a physical dimension at the ground and atmospheric levels, both indoors or outdoors, as observed in many studies [20,35-39].
We need to theoretically and empirically analyzed two parameters, social distancing policy and social transmission isolation, because environmental transmission may play a role in recurrent community transmission of SARS-CoV-2. The epidemiological methods of prediction and control (which are needed to estimate the supply of financial, economic, and public health resources for the predicted number of infected people) lose their effectiveness due to certain aspects of social transmission isolation and SARS-CoV-2’s airborne virulence potential [20,35-39].
This new approach diverges from older approaches, such as the one demonstrated by Hellewell et al , since social distancing and social transmission isolation parameters are different stages under atmospheric conditions, which require further empirical investigation.
Many recent viral infectious diseases (severe acute respiratory syndrome [SARS], Middle Eastern respiratory syndrome [MERS], H1N1) are transmitted similarly to SARS-CoV-2 , but they have different rates of exponential growth . Therefore, it is important to consider not only the causes of transmission, such as the chemical and biological properties of transmission and the virus-human biological affinity but also the emergent virus and human social behavior in the context of the environment [35-40,42-47].
The nonlinear time series of worldwide policies may present a clue in the form of a high asymptotic stability (dissemination network)  about the type of preventive policy measures adopted by each country, as also observed previously by Riou and Althaus  with the k dispersion parameters and the superspreading prediction possibilities.
Evidence for Airborne Transmission
The presence of these epidemiological factors (forms of transmission, biological-chemical affinities, and emergent social virus transmission behavior) associated with the preventive epidemic framework , implemented from January to April 2020, requires considering any given number of infected individuals as an ongoing pandemic threat, since uncertainty prevails.
This led to the conclusion that there was no minimum range of infected individuals that would classify the local epidemic as under control. No policy adopted during the period of interest was more effective than those of China and South Korea. At that time, many authorities thought that the epidemic would have a natural upper limit and posterior descendant tail and would end naturally without any human intervention. However, it has not yet been scientifically proven that the pandemic can end naturally or become seasonal. Therefore, this theoretical observation should not have been used as a preventive measure at that time.
Concerning the evolution of the pandemic from January to April 2020, one important issue reported in the media is the difference between maintaining social physical distancing and full social isolation. Social physical distancing means maintaining physical distance in restaurants, parks, drugstore lines, household activities, neighborhoods (especially low-income neighborhoods), household tree proximity, markets, indoor and outdoor social events, windows and balconies, airplanes, ship balconies, hospital rooms, meetings, delivery or mail activities, prisons, residences, commercial establishments, and industrial facilities .
Full social transmission isolation, meanwhile, requires ground or atmospheric barriers. News and scientific reports [51,52] show that most of China and South Korea  had required residents to wear masks, and full disinfection had been implemented in crowded public spaces [15,53]. There had been some further concerns from public health professionals, as reported by Li et al  and Wong et al .
These policy actions converged with the physical distancing criteria and possible failures, presenting physical transmission isolation barriers for airborne transmission (aerosol-biosols and atmospheric conditions [20,35-39]). Chinazzi et al  discussed community policy actions regarding airplanes. At this point, a counter effect can be seen despite social physical distancing if social activities occur in outdoor spaces without the use of masks or city disinfection. Therefore, risk continues to be present.
Social connection might be one of the unobservable factors of transmission if the virus can spread under atmospheric conditions [35,36,57-60] and is still active in air fluids [20,35-39]. This would mean that a ground preventive framework is insufficient. Most of the recommendations for physical distancing issued during that time addressed the virus’s potential to spread on the ground and through the air via human bodily fluid droplets.
Complex air-fluid scenarios without droplets involved (eg, pollution) were not considered. Wickramasinghe et al  reported several cases of person-to-person transmission patterns in that period, which can be understood as air transmission caused by the lack of virus social transmission isolation policies involving additional barriers, such as masks and city disinfection.
Similar observations were made by Cembalest , based on a brief analysis, and by Pirouz et al , based on mathematical modeling with a deep analysis of how the atmospheric parameters of temperature, humidity, and wind affect the population density output for SARS-CoV-2 infection.
These studies came to the proximal conclusion that atmosphere has a strong impact on the patterns of community virus dissemination in countries that adopted social physical distancing without mask policies and city disinfection. Finally, Poirier et al  examined the weather conditions capable of generating the full transmission patterns without a social transmission barrier for airborne transmission.
reference link : https://publichealth.jmir.org/2021/4/e20699
More information: L. Morawska at Queensland University of Technology in Brisbane, Australia el al., “A paradigm shift to combat indoor respiratory infection,” Science (2021). science.sciencemag.org/cgi/doi … 1126/science.abg2025