By Dr Gareth Kantor
The Great Stink, London, 1858. Human effluent overflows the streets and gutters of the biggest metropolis in the world. The Thames has become a frightening, murky cesspool at the heart of the great city.
In response, parliamentarians, holding their noses against the foul aroma, approve a giant public works programme that results in London’s brilliantly engineered sewer system. Fixing the Great Stink in this way reduces cholera and other waterborne disease, and leads to huge improvements in public health, saving many lives. It helps discredit the ancient, terror-inducing ‘miasma’ (bad air) theory of disease transmission, replacing it with a new idea — germs — and a successful ongoing focus on clean water and sanitation.
January 2020: COVID is about. The Chinese government cuts off the city of Wuhan in a desperate attempt to contain the disease. As the pandemic shuts down most of the world, the World Health Organisation tells us to wash our hands, scrub surfaces, and maintain social distance. Nothing is said about masks or the dangers of being indoors. We are told that a sick person can cough droplets onto your face, or shake your hand, which you then use to rub your nose. The virus can survive on surfaces for hours or days. But the WHO decides against advice to wear masks. Droplets fall to the ground within a metre or two. Just cough into your elbow, and social distance. Wipe surfaces frequently.
April 2020: The WHO affirms that COVID-19 is not airborne, insisting on additional evidence to justify any official change in that view. Meanwhile numerous superspreading events are reported — in restaurants, cruise ships, choir rehearsals — strongly suggesting that SARS-CoV-2 virus in breathed-out air can cross large expanses of indoor air.
May 2021: A little noticed but hugely important change: The WHO says that SARS-CoV-2 is transmitted not only by large droplets, but by tiny particles (aerosols) that can float in air, infecting people many metres away. The miasma theory is back!
The story of this change and what it means for the battle against COVID-19 is a fascinating one. Its late arrival delayed important interventions which might have saved millions of lives.
The aerosol scientists
A year ago, 35 scientists wrote a letter to the WHO. They were concerned about the misunderstanding of the likely mechanism of the spread of COVID-19 by the infectious disease and public health specialists who advise governments and world bodies. The standard public health teaching is that anything under five microns in size can become airborne, and float. Everything else sinks.
The scientists insist that particles expelled from the respiratory tract of infected patients come in a range of sizes, some large droplets likely to fall to the floor, others (up to 100 microns) able to float in trapped air in an enclosed space, depending on heat, humidity, and air speed.
History of an error
In 1934, Harvard engineer William Wells analysed air samples and showed how particles bigger than 100 microns sank within seconds, while smaller particles stayed in the air. But the chief epidemiologist of the Centers for Disease Control, Alexander Langmuir, dismissed Wells’ ideas about airborne transmission as a reversion to the ancient, irrational miasma theory. Langmuir cited studies on miners and factory workers, which showed the mucus of the nose and throat able to filter out particles bigger than five microns. Only the smaller ones could enter deep into the lungs and cause permanent damage. Experiments with rabbits and the TB bacteria confirmed this.
Langmuir emphasised that the problematic particles were smaller than five microns. Scientists mis- understood his observations, taking the size of the particle that transmits tuberculosis (five microns) for a general definition of airborne spread, leaving Wells’ 100-micron threshold behind. This error became accepted as fact. Langmuir later admitted he’d been wrong, but by this time outdated science had underpinned public health policy for decades.
Dislodging the error from decades of doctrine would mean convincing health authorities not only that they were wrong, but that the error was important. Many scientists and researchers have been involved.
During the first SARS outbreak in 2003, investigation of an outbreak at a Hong Kong apartment complex provided strong evidence that the coronavirus could be airborne. The scientists showed that during coughs or sneezes, the heavy droplets are too small in number and the targets — an open mouth, nostrils, eye — too small to produce much infection. They concluded that most colds, flu, and other respiratory illnesses must spread through aerosols instead.
July 2020: 239 scientists and physicians warn that without stronger recommendations for masking and ventilation, airborne spread of SARS- CoV-2 will continue unchecked. A WHO spokesperson resists their use of the term airborne but days later the WHO releases an updated scientific brief, acknowledging that aerosols can’t be ruled out, especially in poorly ventilated places. However the WHO sticks to the 3- to 6-foot rule, advising people to wear masks indoors only if they can’t keep that distance.
October 2020: Another group of scientists and doctors publishes a letter in Science, urging consensus on how infectious particles move, starting by abandoning the five-micron threshold. The same day, the CDC updates its guidance to acknow-ledge that SARS-CoV-2 can spread through aerosols that persist in the air.
December 2020: The WHO recommends that everyone always wear a mask indoors wherever COVID-19 is spreading. They also promote ventilation, but avoid using the term airborne, instead emphasising the types of settings that pose the biggest risks.
30 April 2021: The WHO quietly updates its website, now stating that the virus can spread via aerosols as well as larger droplets. This may have been one of the biggest stories of the pandemic but it passes with no news conference, no major declaration.
May 2021: The CDC makes similar changes to its COVID-19 guidance, placing the inhalation of aerosols first on its list of ways that the disease spreads. But there is no news conference, no press release.
Airborne transmission — avoiding the avoidable?
Current best estimates: while talking, singing or coughing, SARS-CoV-2 is shed: via droplets (55%), short-range (1 — 2 m) aerosols (35%), and long-range aerosols (10%).
Airborne disease transmission means a shift in focus for public health. It would require, for example, good quality face masks to be made available to all; and for public spaces to have their ventilation assessed and possibly upgraded. To combat droplets, the chief precautions are distancing, barriers (masks, visors) and hand hygiene. To fight infectious aerosols, air itself is the enemy. Fortunately, SARS-CoV-2 doesn’t often infect people over long distances if the indoor space is well- ventilated. And the virus definitely spreads most effectively in close proximity to a coughing, talking, or shouting person.
The Third Wave is upon us, what do we do?
What does all this mean to South Africans? We are tired of COVID but COVID is not tired of us. We watch while COVID infection rates inexorably climb the peak for a third time. What else could we do? The recognition that COVID-19 can be spread at a distance, by bad (stale, trapped) air, points to new opportunities.
What we need to do
Improve the ventilation of enclosed spaces. i.e. buildings and public transport. Open doors and windows to ensure a current of air that will replace stale, rebreathed air with fresh air from outside.
Assess ventilation objectively e.g. by means of CO2 meters and analysis by specialist occupational hygienist and industrial engineers. Design or modify HVAC systems to provide cleaner air using filters.
In indoor spaces, wear masks, with good filtering and a snug fit over the nose and mouth. Cloth masks are less protective but can limit spread from infected persons.
Continue to clean hands. No need for deep, frequent, obsessive sanitising of surfaces. No fogging.
Keep a distance from people and avoid crowded indoor spaces. Outdoors is generally safe although close contact with potentially infected persons is unwise, even outdoors.
Quarantine and isolate. i.e. stay home if sick or closely exposed. Get tested; testing is readily available, with rapid turnaround times. Antigen tests are cheap and sufficiently accurate to detect infectious cases.
Last but definitely not least: vaccinate, vaccinate, vaccinate.
Wiping out TB, influenza and stopping the next pandemic
Airborne disease transmission has enormous implications for long-term health policy. By improving ventilation and other factors, it may be possible not only to suppress COVID’s third wave, but to greatly reduce TB and influenza — both major killers in South Africa — as well as to stop runny noses, chest colds, and flu which regularly sweep through society.
Acknowledging the history, and how it has hindered an effective global response to COVID-19, could allow good ventilation and cleaner air to become a pillar of public health policy, a development that could not only hasten the end of this pandemic, but stop future ones; and reduce the enormous disease burden of TB and influenza.
Dr Gareth Kantor is an anaesthesiologist based in Cape Town, a health industry consultant and a health system improver. He is also on the expert panel of GreenFlag Association, a new group that aims to give people the peace of mind that they live, work and relax in safe, healthy, well-ventilated spaces.
• Published in the PDF edition of the June 2021 issue – Download here.
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