Tag: aerosols

COVID Variants Evolving to Improved Airborne Transmission

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A new study found that people infected with SARS-CoV-2 shed significant numbers of virus particles in their breath – and those infected with the Alpha variant put 43 to 100 times more virus into the air than people infected with the original strains. 

The researchers also found that loose-fitting cloth and surgical masks reduced the amount of virus that gets into the air around infected people by about half. The study was published in Clinical Infectious Diseases.

“Our latest study provides further evidence of the importance of airborne transmission,” said Dr Don Milton, Professor, Environmental Health, University of Maryland School of Public Health. “We know that the Delta variant circulating now is even more contagious than the Alpha variant. Our research indicates that the variants just keep getting better at traveling through the air, so we must provide better ventilation and wear tight-fitting masks, in addition to vaccination, to help stop spread of the virus.”

The numbers of airborne virus particles coming from infections with the Alpha variant (the dominant strain circulating at the time this study was conducted) was much more (18 times more) than could be explained by the increased amounts of virus picked up in nasal swabs and saliva. 
Doctoral student Jianyu Lai, a lead author of the study, explained: “We already knew that virus in saliva and nasal swabs was increased in Alpha variant infections. Virus from the nose and mouth might be transmitted by sprays of large droplets up close to an infected person. But, our study shows that the virus in exhaled aerosols is increasing even more.” These major increases in airborne virus from Alpha infections occurred before the arrival of the Delta variant, suggesting that the virus is evolving to have improved airborne transmission.

To test the efficacy of masks in reducing transmission, the researchers measured how much SARS-CoV-2 is exhaled into the air with and without wearing a cloth or surgical mask. They found that face coverings significantly reduced virus-laden particles in the air around the person with COVID by about 50%.

Co-author Dr Jennifer German said, “The take-home messages from this paper are that the coronavirus can be in your exhaled breath, is getting better at being in your exhaled breath, and using a mask reduces the chance of you breathing it on others.” This means that a layered approach to control measures (including improved ventilation, increased filtration, UV air sanitation, and tight-fitting masks, in addition to vaccination) is critical to protect people in public-facing jobs and indoor spaces.

Source: University of Maryland

2-Metre Social Distancing May be Insufficient Indoors

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A new study found that the two-metre physical distance required to avoid the viral shedding from a person infected with COVID caused by speaking or breathing may be insufficient indoors.

Researchers from the Penn State Department of Architectural Engineering found that indoor distances of two metres may not be enough to sufficiently prevent transmission of airborne aerosols. Their results were published online in Sustainable Cities and Society.

“We set out to explore the airborne transport of virus-laden particles released from infected people in buildings,” said first author Gen Pei, a doctoral student in architectural engineering at Penn State. “We investigated the effects of building ventilation and physical distancing as control strategies for indoor exposure to airborne viruses.”

The researchers looked at three factors: the amount and rate of air ventilated through a space, the indoor airflow pattern associated with different ventilation strategies and the aerosol emission mode of breathing versus talking. They also compared transport of tracer gas, usually used to test leaks in air-tight systems, and human respiratory aerosols ranging in size from one to 10 micrometres, a size that can still carry SARS-CoV-2.

“Our study results reveal that virus-laden particles from an infected person’s talking — without a mask — can quickly travel to another person’s breathing zone within one minute, even with a distance of two meters,” said corresponding author Donghyun Rim, associate professor of architectural engineering. “This trend is pronounced in rooms without sufficient ventilation. The results suggest that physical distance alone is not enough to prevent human exposure to exhaled aerosols and should be implemented with other control strategies such as masking and adequate ventilation.”

Aerosols were found to travel farther and more quickly in rooms with displacement ventilation, where fresh air continuously flows from the floor and pushes old air to an exhaust vent near the ceiling. This is the type of ventilation system installed in most residential homes, and it can result in a human breathing zone concentration of viral aerosols seven times higher than mixed-mode ventilation systems. Many commercial buildings have mixed-mode systems, which bring in outside air to dilute the indoor air and result in better air integration as well as tempered aerosol concentrations, according to the researchers.

“This is one of the surprising results: Airborne infection probability could be much higher for residential environments than office environments,” Prof Rim said. “However, in residential environments, operating mechanical fans and stand-alone air cleaners can help reduce infection probability.”

According to Rim, increasing the ventilation and air mixing rates can effectively reduce the transmission distance and potential accumulation of exhaled aerosols, but ventilation and distance are only two options in an arsenal of protective techniques.

“Airborne infection control strategies such as physical distancing, ventilation and mask wearing should be considered together for a layered control,” Prof Rim said.

The researchers are now applying this analysis technique to other kinds of occupied spaces, such as classrooms and transportation environments. 

Source: Pennsylvania State University

Many Respiratory Diseases Are Borne by Aerosols

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As the COVID pandemic forced a close study of airborne transmission, new evidence has challenged the idea that many respiratory pathogens besides SARS-CoV-2 were only carried in the large respiratory droplets from coughs and sneezes of infected individuals. Rather, they also spread through virus-laden microscopic respiratory aerosols.

In a review published in Science, Chia Wang and colleagues discussed recent research regarding airborne transmission of respiratory viruses and how an improved understanding of aerosol transmission will enable better-informed controls to reduce and mitigate airborne transmission.

Most respiratory pathogens were until recently assumed to spread largely in large droplets expirated from an infectious person or transferred from contaminated surfaces. Public health recommendations in mitigating viral spread has, thus far, been guided by this understanding.

It is also known however, that a number of respiratory pathogens, such as influenza and the common cold, spread through infectious respiratory aerosols, which can remain suspended in the air, travelling further and for much longer, infecting those that inhale them.

According to a growing body of evidence, much of which gained from studying the spread of COVID, airborne transmission may be a more dominant mode of respiratory virus transmission than previously thought. Here, Wang et al. highlight how infectious aerosols are generated, travel throughout an environment and deliver their viral payloads to hosts. Before COVID, the maximum size for droplets to be classified as aerosols was 5 micrometres, but this has now been updated to 100 micrometres, because up to this size, droplets can remain suspended in the air for up to 5 seconds from a height of 1.5m and travel one metre to be inhaled by another.

The deal with this under-appreciated threat, the authors described ways to mitigate aerosol transmission at long and short ranges, including improvements to ventilation and airflows, air filtration, UV disinfection and personal face mask fit and design.

Source: News-Medical.Net