Global experts warn of COVID-19 airborne threat
WASHINGTON, United States (AFP) – An international group of 239 scientists has urged authorities, including the World Health Organization, to recognize that the coronavirus can spread in the air at distances well beyond two meters (six feet), and to revise their prevention guidelines accordingly.
In a commentary that appeared in the Oxford Academic journal Clinical Infectious Diseases, researchers wrote that studies have shown “beyond any reasonable doubt” that viruses can travel tens of meters in the air, and analyses of certain spreading events had demonstrated the same was true of the SARS-CoV-2 virus that causes COVID-19.
“There is significant po
tential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale),” wrote the authors, led by Lidia Morawska of the Queensland University of Technology.
“Hand washing and social distancing are appropriate, but in our view, insufficient to provide protection from viruscarrying respiratory microdroplets released into the air by infected people.”
The new paper appears in the Oxford Academic journal Clinical Infectious Diseases.
Their recommendations included greater ventilation for indoor environments; the introduction of high efficiency air filters and ultraviolet lamps; and to avoid overcrowding in buildings and on public transport.
When an infected person coughs or sneezes, they expel droplets of various sizes. Those above five to ten micrometers fall to the ground quickly within a meter or two, while droplets under this size can become suspended in the air in what is called an “aerosol,” remaining aloft for far longer and traveling further.
There has been a vigorous debate in the scientific community about how infectious microdroplets are in the context of COVID19, but for the time being the WHO advises that it occurs in “in specific circumstances” that occur in hospitals, for example when a patient is intubated on a ventilator.
On the other hand, studies of particular spreading events have shown that microdroplet transmission isn't limited to hospitals.
The authors of the new commentary recognized that the evidence for microdroplet transmission was “admittedly incomplete,” but argued that the evidence for large droplets and surface transmission was also incomplete yet still formed the basis for health guidelines.
“Following the precautionary principle, we must address every potentially important pathway to slow the spread of COVID-19,” they wrote.
The paper comes as countries ease their lockdowns, bringing people back to workplaces and students back to schools and colleges.
“We hope that our statement will raise awareness that airborne transmission of COVID-19 is a real risk and that control measures, as outlined above, must be added to the other precautions taken,” they concluded.
For the time being, the WHO advises that the potential for infection from an aerosol occurs “in specific circumstances” mainly in hospitals, for example when a tube is placed down a patient's airway.
On the other hand, some studies of particular spreading events suggest that aerosolization and microdroplet transmission can happen in a variety of settings.
The air flow from an air conditioning unit appeared to waft the coronavirus to several tables in a Chinese restaurant in January where patrons became infected, according to a study that appeared in Emerging Infectious Diseases.
Another study that appeared in a report by the Centers for Disease Control and Prevention indicated that the virus was spread by microdroplets from people singing during a choir practice in Washington state in March.
Fifty-three people fell ill at that event and two died.
That is in addition to the fact that bars jam-packed with people have also emerged as hotspots of contagion, with droplets of all sizes believed to contribute to the spread.
Cath Noakes, a professor of environmental engineering for buildings at the University of Leeds, who contributed to the paper, said COVID-19 doesn't spread in the air as easily as measles or tuberculosis, but is a threat nonetheless.
“COVID-19 is more likely to be ‘opportunistically’ airborne and therefore poses a risk to people who are in the same room for long periods of time,” she added.
The WHO advice is out of step with both the US CDC and its European counterpart.
“We are aware of the article and are reviewing its contents with our technical experts,” the WHO said in response to the new commentary.
‘Precautionary principle’ The authors recognized that the evidence for microdroplet transmission was ''admittedly incomplete,'' but argued that the evidence for large droplets and surface transmission was also incomplete yet still formed the basis for health guidelines.
‘'Following the precautionary principle, we must address every potentially important pathway to slow the spread of COVID-19,’' they wrote.
Put another way, “absence of evidence is not evidence of absence,” said Julian Tang, an associate professor of respiratory sciences at the University of Leicester who contributed to the commentary.
“The WHO says that there is insufficient evidence to prove aerosol/airborne transmission of SARSCoV-2 is happening. We are arguing that there is insufficient proof that aerosol/airborne transmission does not occur,” he said.