As three families lunched at neighbouring tables in a stuffy restaurant in southern China in January, they partook of more than a New Year’s meal. They shared an invisible pathogen apparently carried aloft in an air conditioner’s breeze.
Ten diners later came down with Covid-19, but none of the waiters or other 73 patrons in the room contracted the disease. A video recording and a simulation of airflow dynamics support what scientists had feared, namely that the virus could linger in turbulent air long enough to cause multiple infections.
Almost six months later, the New Year’s feast has become the touchstone in a global debate about how the coronavirus can spread in poorly ventilated spaces — and the extra measures that may be required to halt that. At the core of the controversy remain lingering questions about how often such airborne contamination occurs. After all, the Guangzhou incident shows a majority of diners remained healthy.
The World Health Organization said on Thursday it doesn’t rule out the possibility of airborne transmission in crowded areas or indoor venues with poor ventilation, in an update of a scientific brief. However, the Geneva-based body said more research is needed, because in such cases, there may be alternative explanations as to how the people got sick, such as respiratory droplets that fell onto surfaces.
The WHO faces pressure from scientists led by Lidia Morawska, director of the International Laboratory for Air Quality and Health at Queensland University of Technology, who argue that hand-washing and physical distancing alone aren’t enough to stem infections.
“This problem is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation,” Morawska and a colleague wrote in an open letter published this week and backed by 239 scientists. Officials must endorse other precautions such as increasing ventilation and avoiding recirculating potentially virus-laden air in buildings such as hospitals and schools, they said.
At stake isn’t what happens when an infected person coughs or sneezes globs of virus-laden liquid — a long-established mode of infection — but whether tiny particles known as micro-droplets and aerosols stay afloat long enough to be inhaled and cause infection deep in the lungs.
“Viruses can spread in this way and we need to be aware of that,” said Benjamin Cowling, head of epidemiology and biostatistics at the University of Hong Kong, who assisted China in the early study of transmission dynamics. “But that’s not to scare everybody.”
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Morawska and others are calling on the WHO and similar bodies to recognize airborne transmission as a factor contributing to the spread of Covid-19, which has now sickened more than 11 million people.
‘Not Rocket Science’
Their push is gaining urgency as workplaces, schools, and colleges reopen. In the US, President Donald Trump rejected school-reopening guidelines that included increasing the circulation of outdoor air as too difficult.
“This is not rocket science,” Morawska said in an interview. “We know how to deal with ventilation.”
Some scientists point to the fact that the new pathogen hasn’t spread explosively across hospitals as evidence that it isn’t as contagious by air as flu or measles. The WHO says its existing recommendations, such as avoiding closed settings and ventilating indoor environments, do take into consideration the virus’s potential airborne nature. However, it stopped short of saying that such transmission is a proven threat in its scientific brief.
While the Morawska-led group recommended high efficiency air filtration and germicidal ultraviolet lights be used, it also pointed to simpler protective measures, like supplying clean outdoor air and avoiding overcrowding on public transport.
“Ventilation can be particularly important,” said the University of Hong Kong’s Cowling, who reviewed the letter. “Spending time outdoors can be a really good thing to do to avoid the risk of transmission of Covid-19.”
The WHO needs to concede that the new coronavirus can spread via the airborne route, according to Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
“We are long overdue for the WHO to confront the blind spot it has had for accepting the critical importance of airborne transmission of respiratory pathogens,” he said Monday in his center’s daily news bulletin.
Morawska, 67, started looking at airborne transmission of infectious disease after the SARS epidemic. During the outbreak, she was asked by the WHO to join a team of aerosol scientists to investigate contagion at Hong Kong’s Amoy Gardens housing estate, where a virus-laden plume emanating from a patient with diarrhoea was implicated in hundreds of cases.
‘Get Something Done’
The epidemic ended before the investigation could properly start, but the airborne hypothesis piqued Morawska’s interest. At the time she’d been researching the impact of air quality on human health, but after she discovered only three papers were published on airborne transmission of infectious diseases, she spent the next 17 years doing her own investigations.
Among her discoveries, she showed that Pseudomonas aeruginosa, a bacterium known to sicken cystic fibrosis and hospital patients, could linger in the air 45 minutes after it was emitted from a cough. Morawska always wanted to understand more about the aerosol transmission of SARS. Once the epidemic was over though, she struggled to get grants for the research.
“No one was interested,” she said. Since SARS-CoV-2 emerged, she’s written or contributed to more than a dozen papers on the potential for the pandemic’s airborne spread via microscopic aerosols and droplets, which she hopes will inform “practices which are necessary to control this infection” as well as influenza and other pathogens.
“This makes me even more determined to get something done about this,” Morawska said. “Once this pandemic is over — which probably won’t happen that quickly — and these issues are not recognized and not taken care of, then we will be in the same situation during the next pandemic.”
(This story has been published from a wire agency feed without modifications to the text. Only the headline has been changed.)
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