An in-depth study into the airborne transmission of SARS-CoV-2 and the need for Indoor Air Quality (IAQ) standards
Airborne Transmission
Eighteen months after the first confirmed case of a pneumonia caused by a novel coronavirus, the Centers for Disease Control and Prevention (CDC) and the World Health Organisation (WHO) have finally acknowledged that the virus that causes COVID-19, SARS-CoV-2, is airborne. Since the beginning of the pandemic, the WHO and CDC, among others, had advised that the primary paths for the spread of COVID-19 were droplets, surfaces and objects. This recent acknowledgement is crucial because it will change the basis of health protocols and policies all over the world.
Updated on May 7th 2021, the CDC website now states that the SARS-CoV-2 virus is transmitted by exposure to infectious respiratory fluids. It goes on to say that “The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory fluids carrying infectious virus. Exposure occurs in three principal ways: (1) inhalation of very fine respiratory droplets and aerosol particles, (2) deposition of respiratory droplets and particles on exposed mucous membranes in the mouth, nose, or eye by direct splashes and sprays, and (3) touching mucous membranes with hands that have been soiled either directly by virus-containing respiratory fluids or indirectly by touching surfaces with virus on them.”
Similarly the WHO website has been updated and now acknowledges that “The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols remain suspended in the air or travel farther than 1 metre (long-range).”
Among many in the medical and scientific community, this change seemed like a long time coming. The updates appeared shortly after an article entitled “Ten scientific reasons in support of airborne transmission of SARS-CoV-2” appeared in the respected medical journal the Lancet which put it rather bluntly: “There is consistent, strong evidence that SARS-CoV-2 is spread by airborne transmission. Although other routes can contribute, we believe that the airborne route is likely to be dominant. The public health community should act accordingly and without further delay.”
The reasons this conclusion was reached were many, among the most convincing being:
- transmission observed at superspreader events
- long-range transmission observed in quarantine hotels between people who did not spend time in the same room
- the virus has been found in air filters and building ducts—or locations that could be reached only by aerosols—in hospitals with COVID-19 patients
- transmission is higher indoors than outdoors and is substantially reduced by indoor ventilation
- contact tracing has shown that conditions such as ventilation play a significant factor in infections
- caged animals have contracted the virus from other infected animals staying in separate enclosures but connected through an air duct
Conversely, no study has provided consistent evidence refuting airborne transmission and there is limited supporting evidence that the virus can spread through other means such as objects or through large droplets.
The recognition of airborne transmission by the CDC and WHO is imperative because it directly influences how the virus is combatted. Chiefly, because we know that an aerosolized droplet can stay in the air longer and can travel further than 3 feet—up to 8 ft in a closed space without ventilation- it means that
- buildings will have to ensure proper ventilation to reduce spread of disease.
- the wearing of masks indoors and among unvaccinated individuals may be more important.
- upgrading of office heating, ventilation and air conditioning systems to improve indoor air quality could be critical.
Resistance To Change
Why did it take so long for these large institutions to acknowledge this? After all, back in November 2020, 239 scientists signed an open letter to medical communities and governing bodies about the potential risk of airborne transmission. In it the scientists said ‘We appeal to the medical community and to the relevant national and international bodies to recognize the potential for airborne spread of coronavirus disease 2019 (COVID-19).”
This resistance to changing popular thinking isn’t a new phenomenon.
When people in London were dying of cholera in the 1850s, scientists made a major scientific misperception- that the disease was airborne. But one British obstetrician called John Snow refused to accept this, believing microorganisms in contaminated water were the reason. Similarly, against popular thinking of the time, Hungarian physician Ignaz Semmelweis showed that handwashing before delivering a baby greatly reduced postpartum infections. Thankfully, but not without needing a lot of convincing, scientists did eventually agree that in these cases that water and hands—not air—were the vector for disease.
Dr John Snow
Frequent large-scale epidemics of cholera were an accepted part of life in European cities in the 19thcentury and were believed to be spread through the air or from “miasma” – stinking fumes from organic or rotting material. However John Snow had long believed that water contaminated by sewage was the cause of cholera and had, in 1849, published a poorly received article outlining his theory.
Like most major cities in the 19th century, use of town wells and communal pumps to obtain water combined with primitive or non-existent septic systems meant that people living in London had access only to very poor quality water. Most homes and businesses dumped untreated sewage and animal waste directly into the Thames River or into open pits called “cesspools”, in the mistaken belief that they were getting rid of the miasma, only to be aggravating the problem. Water companies often bottled water from the Thames and delivered it to pubs, breweries and other businesses.
When in August of 1854 an outbreak of cholera struck Soho in the city of London, Dr. Snow was determined to prove his theory that contaminated water was the cause of the outbreak. He suspected the water of the street-pump in Broad Street may have been be the source and his subsequent pioneering medical research confirmed his suspicions.
In September 1854, Snow convinced the town officials to take the handle off the pump, making it impossible to draw water. The outbreak of cholera almost immediately came to a stop.
Despite the success of Snow’s theory, officials refused to improve the conditions of the cesspools and sewers. The Board of Health issued a report that said, “we see no reason to adopt this belief” and dismissed Snow’s evidence as mere “suggestions.”
Through dogged research, it was eventually revealed that a woman, who lived on Broad Street, whose child who had contracted cholera from some other source, washed the baby’s diapers in water which she then dumped into a leaky cesspool just three feet from the Broad Street pump. It still took many years before public officials made the improvements necessary to ensure clean water for the people of London.
And it was nearly thirty years later, when Robert Koch isolated the bacterium Vibrio cholerae, the “poison” Snow believed caused cholera, before there was widespread acceptance of the fact that cholera is spread only through unsanitary water or food supply sources. Finally, sewage drainage systems and water purification systems began to be introduced in cities and towns in the following decades, vastly reducing the threats of cholera, typhoid and many other waterborne diseases.
Sadly, the World Health Organization estimates 78% of the people in developing countries are still without clean water supplies today, and up to 85% of those people don’t live in areas with adequate sewage treatment, making cholera outbreaks an ongoing concern in far too many parts of the world.
Dr. Ignaz Semmelweis
Ignaz Semmelweis, born in 1818 in Hungary, was the physician who discovered the cause of puerperal (childbed) fever. Puerperal or childbed fever, also known as postpartum infection, occurs when bacteria infect the uterus and surrounding areas after a woman gives birth and it has the potential to cause huge morbidity and mortality. In fact during the period when Semmelweis worked at the obstetric clinic in Vienna, the mortality rates from obstetric complications was 25-30%.
Most medics had reconciled themselves to the inevitability of the disease that was presumed to be caused by overcrowding, poor ventilation, the onset of lactation or miasma. Refusing to accept this, Semmelweis proceeded to investigate its cause over the strong objections of his superior, who, like most of his peers, had accepted that the disease was unpreventable.
Semmelweis observed that the death rate from postpartum infection among women in the first division of the clinic was two or three times as high as among those in the second division. The two divisions were identical with the exception that students were taught in the first and not in the second. Realising that the students were coming from the anatomy room where they handled cadavers, he introduced a mandatory hand washing regimen. The mortality rate fell to about 2%—down to the same level as the division one clinic. Later he started washing the medical instruments and the rate decreased to about 1%. In March and August of 1848 no woman died in childbirth in his division.
Despite this seemingly obvious causal relationship, Semmelweis was met with much resistance to his theory. He spent a lifetime trying to convince the medical community but without success and he eventually died in an insane asylum at the age of 47. It wasn’t until two decades later that his work was reconsidered and he was final given well-deserved credit. Only after Pasteur, Koch, and Lister had advanced antiseptic techniques and germ theory was the value of hand washing properly understood.
These examples from so long ago help demonstrate the tendency for the scientific community to drag their feet when it comes to change and it is this reluctance that may be attributed to their resistance to the idea that COVID-19 is spread mainly by aerosolization and to the broader issue of the necessity to treat our indoor air like we treat our water.
Protection Against Respiratory Illness and Airborne Transmission – Treat our air like we treat our drinking water
In John Snow’s time, people accepted waterborne diseases as a way of life just as we currently accept colds and the flu as a way of life but if we were to treat our air like we treat our drinking water, we could greatly reduce respiratory infections. Clean indoor air will protect not only against COVID-19 but also other respiratory illnesses. It is phenomenal to think that our acceptance of airborne diseases like influenza may, because of Covid-19 , become a thing of the past.
Let’s not let an opportunity presented to us by a deadly disease pass us by. Our apathy towards this is unacceptable. In 1945, scientist William Wells published a paper in ‘The Scientific Monthly” arguing that while we were investing in disinfecting water and keeping our food clean, we had done nothing for our indoor air. His research on measles and tuberculosis-both airborne pathogens-supported his pleas, but the world didn’t listen. Surely by now we have learned that outdated and unsupported thinking and attitudes can cost lives.
Now is the time to change.
When we design a building, we shouldn’t just plan for the minimum amount of ventilation, but build with respiratory diseases and future pandemics in mind. Until now, buildings have focused on thermal comfort, odour control and energy use but have largely ignored ventilation systems to mitigate the spread of disease. We 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. There are currently no guidelines, globally or in the U.S., that regulate or provide standards to modify bacteria or viruses in indoor air. Again, our apathetic attitude. In the developed world we expect clean water from our taps so why shouldn’t we have the same expectations for our indoor air. Clean, toxin and pathogen-free air in our indoor spaces should be a no-brainer. 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.
Paradigm Shift
In an article published on May 14th a group of 39 researchers from 14 countries called for a “paradigm shift” in combating airborne pathogens such as SARS-CoV-2 demanding universal recognition that respiratory infections can be prevented by improving indoor ventilation systems. The summary of the article entitled “A paradigm shift to combat indoor respiratory infection”, reads as follows:
‘There is great disparity in the way we think about and address different sources of environmental infection. Governments have for decades promulgated a large amount of legislation and invested heavily in food safety, sanitation, and drinking water for public health purposes. By contrast, airborne pathogens and respiratory infections, whether seasonal influenza or COVID-19, are addressed fairly weakly, if at all, in terms of regulations, standards, and building design and operation, pertaining to the air we breathe. We suggest that the rapid growth in our understanding of the mechanisms behind respiratory infection transmission should drive a paradigm shift in how we view and address the transmission of respiratory infections to protect against unnecessary suffering and economic losses. It starts with a recognition that preventing respiratory infection, like reducing waterborne or foodborne disease, is a tractable problem.’
The researchers also advocate for indoor air quality (IAQ) standards to be established and enforced globally and furthermore for this information to be available to the public. Such an overhaul in ventilation standards would be similar in impact and scale to the 19th century transformation that took place when cities started organizing clean water supplies and centralized sewage systems. And look how that changed the world.
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