Aerosolized Transmission

This forum is to discuss general things concerning TSOI.
Post Reply
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Study links SARS-CoV-2 seasonality to increased spread at lower temperatures

10/15/20 ... tures.aspx

In a recent paper available on the bioRxiv* preprint server, US researchers show that individual particles of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) undergo structural destabilization at relatively mild but elevated temperatures – strengthening the case for coronavirus disease (COVID-19) resurgence in the winter.

A common transmission route for SARS-CoV-2, the causative agent of COVID-19 disease, is through aerosols created during sharp exhalation events, such as coughing or sneezing. Furthermore, it is known that viral particles frequently spread after their deposition on different surfaces.

Seasonal dependence and variation according to climate were expected early in the pandemic due to certain similarities with other human coronavirus diseases; nonetheless, we did not witness a sharp fall in the rates of infections during the summer of 2020, resulting in widespread doubts about COVID-19 seasonality.

Alongside envelope and spike proteins, SARS-CoV-2 also packages the RNA genome encapsidated with manifold copies of nucleocapsid proteins. Moreover, the virus also harbors thousands of copies of the matrix protein. All of this opens the door for constructing virus-like particles (without genetic material) amenable for research.

The value of virus-like particles

In this new paper, researchers from the University of Utah in Salt Lake City and the University of California in Davis (US) have employed atomic force microscopy to investigate the structural stability of individual SARS-CoV-2 virus-like particles at a range of different temperatures – before or after immobilization and drying out on a functionalized glass surface.

"The ability to make virus like particles based on the SARS-CoV-2 genome, combined with abundant available structural information allowing for high precision design strategies opens a unique opportunity for fast progress and allowed us to overcome the safety concerns associated with experiments on the full virus", study authors explain their methodological choice.

In a nutshell, the researchers have utilized this technology to appraise the viral envelope's stability and associated proteins (i.e., matrix, envelope, and spike) under diverse environmental conditions.

The same research group has previously shown that (akin to SARS-CoV) the expression of SARS-CoV-2 matrix, envelope, and spike proteins in transfected human cells is enough for the formation and release of virus-like particles through the same biological pathway that is used by the fully infectious virus.

Viral stability in different temperatures

"We demonstrate that even a mild temperature increase, commensurate with what is common for summer warming, leads to a dramatic disruption of viral structural stability, especially when the heat is applied in the dry state", study authors summarize their findings.

The use of atomic force microscopy revealed that only a handful of SARS-CoV-2 viral particles retain their shape, and even those extraordinary particles degraded almost instantly during scanning, which means they are likely already structurally impaired.

One unexpected finding stemming from this study is how little heating it takes to degrade virus-like particles; more specifically, just 34 °C for as little as 30 minutes was sufficient for a rather dramatic effect. The effect is weaker for particles exposed to elevated temperatures in solution and stronger for exposing them in a dry state.

Conversely, surfaces at 22 °C do not aid in their swift degradation, suggesting that common indoor surfaces and those located outdoors during colder seasons may indeed foster prolonged viral survival and, possibly, increased and extended viral spread.
A single particle perspective on viral seasonality

The results of this study are consistent with other available non-mechanistic studies of viral infectivity and provide a single particle perspective on viral seasonality – consolidating at the same time the case for the resurgence of COVID-19 in the winter.

"It is hard to estimate how all individual contributing factors would contribute to the epidemiological picture on the ground," caution study authors in this exciting bioRxiv paper.

"Nonetheless, our findings draw parallels between the stability of SARS-CoV-2 and the original SARS viruses and add to a growing body of research suggesting more viral spread is likely at lower temperatures via a variety of possible contributing factors", they add.

And since another big wave of the outbreak is looming while we enter the winter season, there is a pressing need to conduct further mechanistic studies of both COVID-19 and the SARS-CoV-2 virus, as these findings will be pivotal for policy decisions.

*Important Notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal references:

Sharma, A. et al. (2020). Structural stability of SARS-CoV-2 degrades with temperature. bioRxiv., ... 2.336818v1

Additional source:

Swann, H. et al. (2020). Minimal system for assembly of SARS-CoV-2 virus like particles. bioRxiv., ... 1.128058v3
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Engineers visualize how speaking spreads a virus

10/19/20 ... virus.aspx

The coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), primarily spreads through respiratory droplets expelled when a person coughs, sneezes, breathes or speaks.

A team of researchers and engineers at Princeton University has provided a visualization of how speaking produces and expels saliva droplets into the air. The smallest droplets can be inhaled by people, which is the primary mode of transmission of infections such as COVID-19.

A better understanding of how SARS-CoV-2 spreads should lead to new or better mitigation strategies and help slow down the pandemic, which has now claimed over 1.11 million lives worldwide and infected nearly 40 million people.

The study

The study, published in the journal Physical Review Fluids, highlights how the virus spreads through these respiratory as speech is a potent route for viral transmission of COVID-19.

The team aimed to show with high-speed imaging how phonation of common stop consonants, which are found in most of the world's spoken languages, form and extend salivary fragments in a few milliseconds as moist lips open.

When the mouth opens to produce speech sounds, a film of lubricating saliva spreads across the lips. When a person opens his mouth to speak, the film breaks into filaments. The lungs' airflow and outward from the mouth stretch the filaments until they break and scatter into the air as tiny droplets. All these happens within fractions of a second.

The research team visualized the formation of the droplets when speaking. The camera was zoomed in on the speaker's mouth and recorded a video at an extremely detail-revealing 5,000 frames per second under intense illumination. The footage was recorded at the millisecond level, frame-by-frame perspective, and showed the formation of a lubricating salivary layer on the lips as the speaker pronounced consonants.

“Both saliva viscoelasticity and airflow associated with the plosion of stop consonants are essential for stabilizing and subsequently forming centimeter-scale thin filaments, tens of microns in diameter, that break into speech droplets,” the researchers wrote in the paper.

Stop consonants

The researchers also found that the mechanism that produces these droplets are more pronounced when people use stop-consonants, including "p" and "b."

When people use these "plosives," the lips firmly press together to produce the sound. Hence, there is more power and force for the droplets to disperse into the air. Other consonants that produce droplets at a much greater rate are "t" and "d."

“We have made the first direct visualization of the mechanism that produces droplets in the oral cavity during everyday speech. Our study provides insights into the origin of droplets when people talk, which can aid in curbing the spread of diseases like COVID-19,” Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering, said.

COVID-19 transmission

Early in the pandemic, little was known about how the virus spread. Since it was a relative of other infections in the past, such as the severe acute respiratory syndrome (SARS) in 2002 and the Middle East respiratory syndrome (MERS) in 2012, many scientists believed that the main transmission route was through respiratory droplets.

Recent updates from the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) have acknowledged that the pathogen can spread through tiny aerosols, which hang and travel through the air. These aerosols can be produced even when a person speaks, breathes, and sings.

In the current study, the researchers wanted to bring their expertise in fluid mechanics to provide an insight into how COVID-19 spreads, explaining why the virus has spread at a fast rate across nations.

They focused on asymptomatic transmission, which is described as the virus's spread from people who were not coughing and sneezing. It turns out. The virus can also spread when people speak.

The study's findings strengthen the importance of wearing masks and practicing social distancing, especially in public places. The researchers also believe that wearing masks should effectively contain a significant number of expelled aerosols. Further, they said that the simple way of wearing lip balm should cut down on droplet formation when talking.


Princeton University. (2020). How exactly do we spread droplets as we talk? Engineers found out. ... -found-out
COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU) - ... 7b48e9ecf6

Journal reference:

Abkarian, M., and Stone, A. (2020). Stretching and break-up of saliva filaments during speech: A route for pathogen aerosolization and its potential mitigation. Physical Review Fluids. ... s.5.102301
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

The coronavirus is airborne -- what that means for you

Aerosols, droplets and microparticles. Here's what you should know about airborne transmission of COVID-19.

10/9/20 ... consensus/

Since the early days of the coronavirus pandemic, scientists and doctors have warned of airborne transmission of SARS-CoV-2, the virus that causes COVID-19. Finally, in October 2020 -- seven months into the pandemic -- public health agencies have acknowledged the potential of airborne spread.

We've long known about the transmission of the coronavirus via respiratory droplets from coughs and sneezes, which is why everyone is encouraged to wear masks and stay six feet away from each other. The question of airborne spread has been contentious for months, with some scientists arguing for preventive guidance, but public health agencies delayed in recognizing airborne transmission. However, we now know that six feet isn't far enough to prevent inhalation of aerosolized particles.

This acknowledgement, and the fact it took so long, has led to some confusion about the way the novel coronavirus spreads, reinforcing the need for precautionary measures. Learn what experts have to say about the airborne spread of COVID-19 and what it means for you.

Is the coronavirus airborne?

The Centers for Disease Control and Prevention published guidelines on Oct. 5, declaring the novel coronavirus is indeed airborne.

"From what we currently know, the preponderance of the evidence is that transmission is mainly through respiratory droplets and aerosols, with contamination of surfaces playing a limited role in transmission," says Dr. Davidson Hamer, professor of global health and medicine at the Boston University School of Public Health and School of Medicine.

According to the CDC, the coronavirus mainly spreads through direct and close contact, such as talking to someone without a mask in close quarters. It sometimes spreads through airborne transmission and occasionally spreads through indirect contact, such as touching infected surfaces and then touching your nose, mouth or eyes.

What does it mean when a virus is airborne?

According to the World Health Organization, "airborne transmission is defined as the spread of an infectious agent caused by the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in air over long distances and time."

In other words, when a virus is airborne, it spreads through the air via microscopic particles that can be inhaled.

Dr. Joseph Allen, director of the Healthy Buildings program at Harvard and an assistant professor of exposure assessment science at the T.H. Chan School of Public Health, says the public simply needs to understand that this means our "safe zone" of six feet doesn't necessarily exist.

"Of course, it's a bit more nuanced than that," he says, "but the public has been told that exposure happens within six feet." The truth is, Allen continues, we generate particles that can travel further than that. And because of their small size, they also stay in the air longer.

Wait, aren't 'respiratory droplets' airborne anyway?

This is where the confusion starts, says Dr. Philip Tierno, professor of microbiology and pathology at New York University School of Medicine. The term "respiratory droplets" refers only to where the particles come from. A respiratory droplet -- something that comes from your respiratory tract and is expelled from your nose or mouth -- can "be micro or macro in size," Tierno explains.

Every time you sneeze or cough, you release large and small particles. The larger particles travel a short way (six or so feet) and then settle to the ground, falling because of gravity. The smaller particles remain suspended in the air, traveling much farther and resisting the effect of gravity, Tierno says.

Both large and small particles can be released when someone coughs or sneezes, but also when people talk, sing and shout -- you may remember the cluster of cases linked to a choir practice with one symptomatic person. The aerosolization of particles is related to the volume of vocalization, according to the authors of the case study.

Both types of particles are still respiratory droplets, Tierno says, so yes, technically, some respiratory droplets are truly airborne.

What's the difference between aerosols and droplets?

The confusion continues. "The problem is that people use these terms interchangeably," Tierno says, "when in reality they mean different things."

You may have seen several terms floating around the internet, including droplet, aerosol and microdroplet. Microdroplets and aerosols are synonymous: These terms both refer to fine particles that can exist in the air for long periods of time and travel long distances. Droplets, on the other hand, are larger and do not travel as far.

There's a longstanding (circa 1930s) standard in the medical and scientific communities that five microns serves as the "fence" between airborne particles and non-airborne particles. Anything larger than five microns is thought to settle to the ground within six feet -- this belief informed the six-foot social distance barrier that's now commonplace.

However, a letter from researchers published on Oct. 5 urges the scientific community to change this definition. A standard of 100 microns would be more appropriate, the researchers wrote, because in confined spaces, viruses in aerosols smaller than 100 microns can live for long periods of time.

Respiratory particles exist on a continuum, Allen says. "The reality is that [people] release particles of many different sizes, from less than five microns to way more. The medical community has long thought that a five-micron particle settles to the ground in less than six feet, but this is not always the case."

Other factors, like ventilation, environment and velocity can affect how quickly a particle of any size settles, he says. Cigarette smoke might help you visualize this -- if you stand 15 feet away from someone smoking a cigarette outdoors and the wind is still, you probably won't notice the smoke. But with a breeze, the particles of cigarette smoke will quickly travel to you, even with that distance of 15 feet.

"The point for the public is this: There are a range of sizes [of particles], some of which can travel longer than six feet," Allen says.

Has COVID-19 been airborne this whole time?

According to many scientists and doctors, the CDC has severely lagged in identifying the novel coronavirus as airborne. The same thing happened during the early months of the pandemic, when the CDC and WHO delayed labeling it a pandemic.

Many scientists and doctors began lobbying the CDC as early as February 2020 in an attempt to get the public health agency to classify SARS-CoV-2 as an airborne virus. In July 2020, nearly 250 scientists and doctors wrote an open letter to public health agencies urging them to address airborne transmission.

It's unlikely anything fundamental -- like the mode of transmission -- has changed about the novel coronavirus since it began spreading in early 2020. It's more likely that now, seven months in, the evidence is clear enough to definitely say COVID-19 can spread through airborne particles.

Why didn't the CDC tell us the coronavirus was airborne?

Some say the CDC was trying to avoid adding to public fear or anxiety about the coronavirus, but this logic is faulty, Allen says. "This is risk communication 101," he says. "You don't hold back information. You have to be transparent about what's happening to establish trust and allow people to act accordingly to protect themselves and others."

Allen, who first wrote about airborne transmission of the coronavirus in February, says he doesn't know what took the CDC so long to acknowledge airborne spread. "We [doctors] were excited a few weeks ago that they acknowledged it, and then they walked it back," he says.

"The result is a confused public," Allen says. "The science is what the science is," and people can't make informed decisions without knowing the truth. Allen says he supposes many more people would've taken basic precautions early in the pandemic had public health officials declared the virus airborne.

Others say the CDC's lack of acknowledgement was of the presidency's accord. "The CDC unfortunately is affected by the White House," Tierno says. "Anything the CDC does can be politically infused. They may not have done this had they had no pressure on them."

Does this mean the coronavirus is more infectious?

No, the identification of airborne transmission doesn't mean the novel coronavirus is more infectious than it already was.

"There's a fundamental misunderstanding that all airborne viruses are highly infectious through airborne transmission," Allen says. "Not all airborne viruses are like tuberculosis or measles," both of which have high and rapid infection rates.

It does mean, however, that the standard of six feet isn't always enough to prevent infection, especially in poorly ventilated areas.

It's still not clear how many cases have occurred due to airborne transmission, and without a solid contact-tracing infrastructure, that's something we may never know, says Allen.

How long does the coronavirus live in the air?

There's no finite number of minutes or hours known yet. Estimates range from just a few hours up to 12 hours or more. Tulane University, for instance, reported that COVID-19 can remain in the air for up to 16 hours.

"'Hours' is typical, but remains largely undefined," Tierno says, "which is an important consideration."

Dr. Roshni Mathew, associate medical director of infection prevention and control at Stanford Children's Health, says it's important to remember that finding the virus's RNA in air doesn't automatically equate to transmission.

"Just having aerosols or finding virus particles does not equate to transmissibility, as there are other factors to consider," she says, notably whether or not the virus is actually viable, meaning able to infect you. The WHO reports that in several studies that found virus particles in the air, the researchers did not find viable particles.

How far can the coronavirus travel in the air?

"The virus that causes COVID-19 is still under intense research," Hamer says, "but it is understood that [larger] respiratory droplets from infected individuals can travel at least a few feet through the air to other persons within close contact."

Aerosolized particles are lighter, so they are able to travel further through the air, Hamer continues, noting that some evidence has shown aerosols containing viruses can travel up to 18 feet. One study conducted in China suggests that aerosolized SARS-CoV-2 can spread up to four meters, or about 13 feet. Another report from April estimates the virus can spread up to 10 meters, or about 32 feet.

Again, environmental factors must be considered. Wind can carry particles, even larger ones, farther than six feet.

What this means for you

Most importantly, everyone should be aware that airborne transmission of COVID-19 means six feet isn't a magic number. The novel coronavirus can spread farther than that, and it's important to keep that in mind, especially when indoors.

The current best practices for preventing the spread of COVID-19 are still our best protection, Hamer says. "The same personal protective measures should be adhered to, including wearing of face masks, good hand hygiene and practicing social distance measures," he says, emphasizing that social distancing means at least six feet apart.

Knowing the novel coronavirus is airborne, people should pay more attention to the ventilation and air quality of their homes and other environments they frequent, Allen says.

"This reinforces the need for masks; it reinforces the fact that we shouldn't be spending time indoors in crowded conditions or unventilated areas," Allen says. "And it matters that the CDC said this."

"It matters," Allen emphasizes, "because before, it was just scientists saying it. It wasn't official. Now it's official, and going against this is going against [CDC] guidance."

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Universal testing in schools may be needed to prevent SARS-CoV-2 transmission

10/25/20 ... ssion.aspx

Researchers at Simon Fraser University in Canada have warned that within the school setting, even small differences in individuals' contribution, their environment, and their activities to the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) result in highly variable sizes of transmission clusters.

SARS-CoV-2 is the virus responsible for the current coronavirus disease 2019 (COVID-19) pandemic that continues to sweep the globe posing a significant threat to global public health and the economy.

The team’s modeling study also found that none of the mitigation measures initiated to control viral spread once a symptomatic individual tested positive was effective at preventing large transmission clusters.

Study authors Paul Tupper and Caroline Colijn say that the only measure that does appear to be effective at accomplishing this prevention is rapid universal onsite monitoring.

The researchers also say the findings could apply to other settings where individuals spend many hours with the same group of 20 to 30 people, such as the workplace.

The paper is available on the server medRxiv*, while the article undergoes peer review.

Closing schools as part of control efforts

As part of efforts to control the COVID-19 pandemic, many countries implemented widespread intervention measures, including school closures. However, there is significant uncertainty surrounding the role children and schools play in the transmission of SARS-CoV-2.

Studies conducted during the early stages of the pandemic indicated that children were unlikely to be very infectious.

However, a growing body of evidence suggests that children and adolescents can acquire and transmit SARS-CoV-2 in the school setting and that large transmission clusters and outbreaks can occur.

Schools started to reopen with mitigation measures in place

Given the damaging and costly impact of school closures, many countries have started to reopen schools while ensuring control measures are in place.

A range of mitigation approaches are being used to limit viral spread within the school setting and transmission to the broader community.

It is essential to understand how much and via which routes transmission occurs in the classroom environment so that the costs of schools opening versus staying closed can be accurately weighed and so that the most effective interventions can be identified.

“If we are to maintain open schools, it is necessary to prevent large school transmission clusters, even if they are expected to be rare,” said the researchers.

What did the researchers do?

Tupper and Colijn used a stochastic individual-based model, which enabled them to consider the different observations made so far regarding cluster sizes and control measures.

The team considered two sources of transmission heterogeneity: the person-to-person variation in infectiousness and the variation in how a particular activity or environment might affect transmission rate.

The researchers also considered the potential for pre-symptomatic or asymptomatic transmission and transmission outside of a particular set of contacts through mixing with people outside of the group or through aerosol transmission.

The transmission was modeled on the elementary school and high school settings in British Columbia once schools had reopened in September 2020.

What did the study find?

None of the implemented interventions due to a symptomatic individual testing positive for infection were effective at preventing large transmission clusters, even when all pupils in the class self-isolated following the individuals’ positive result.

The researchers say the findings point to three main ways in which transmission could be prevented.

One approach would be reducing community transmission to ensure exposures are rare and that the risk of introductions into schools is minimized. Another approach would be testing for infection, not only to prevent an initial transmission cluster but also to prevent any further ones.

The authors say that regular testing of all individuals, irrespective of whether they have symptoms, is more effective than only testing symptomatic people.

“Rapid regular universal monitoring is far superior in preventing large clusters to testing that is initiated upon detection of a symptomatic case, even if a whole class is then tested soon afterward,” they write.

Finally, steps should be taken to control the environment's potential contribution to the variation in transmission rates. Data could be gathered on classroom size and organization, ventilation, and student numbers, for example, this data is further linked to follow-up studies on cluster size.

The findings apply to other settings

The researchers say that although this study focused on the classroom setting, the model used here could apply to other settings where people spend many hours per day together in groups of around 20 to 30 and have close contact with a subset of this group.

“Many workplaces may be well represented by our model and conclusions,” suggests the team.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

Tupper P and Colijn C. COVID-19’s unfortunate events in schools: mitigating classroom clusters in the context of variable transmission. medRxiv, 2020. doi:, ... 20216267v1
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Study of SARS-CoV-2 outbreak in meat processing plant suggests aerosol transmission in confined places

10/28/20 ... laces.aspx

The importance of maintaining high-quality air flow to restrict transmission of SARS-CoV-2 in confined workspaces has been strongly indicated by the investigation of an outbreak of the virus at a German meat processing plant during May and June 2020. The study, published in EMBO Molecular Medicine, found that the outbreak originated from a single worker on the meat processing production line. It also concluded that in such confined spaces where unfiltered air is recirculated at low rates of external air exchange, transmission of SARS-CoV-2 can occur over distances of at least eight meters.

The study is relevant for many workplaces, but especially significant for the meat and fish processing industries that emerged early during the pandemic as hotspots for SARS-CoV-2 around the world. A combination of environmental conditions and operational practices with close proximity between many workers on production lines engaged in physically demanding tasks promoting heavy breathing, along with shared housing and transportation, all conspire to encourage viral transmission in such plants.

Melanie Brinkmann from Technische Universität Braunschweig and Helmholtz Centre for Infection Research, Germany, Nicole Fischer from University Medical Center Hamburg-Eppendorf, Hamburg, Germany and Adam Grundhoff from the Heinrich Pette Institute for Experimental Virology, Hamburg, Germany, together with a group of further researchers conducted a multifactorial investigation at Germany’s largest meat processing plant in the state of North Rhine Westphalia, where the outbreak occurred. They traced the events starting with an initial outbreak in May, followed by increasing numbers culminating in more than 1,400 positive cases having been identified by health authorities by 23 June.

The investigation of timing of infection events, spatial relationship between workers, climate and ventilation conditions, sharing of housing and transport, and full-length SARS-CoV-2 genotypes, demonstrated that a single employee transmitted the virus to more than 60% of co-workers in a distance of eight meters.

Viral genome sequencing was conducted and showed that all the cases shared a common set of mutations representing a novel sub-branch in the SARS-CoV-2 C20 clade. Furthermore, the same set of mutations was identified in samples collected in the time period between the initial infection cluster in May and the subsequent large outbreak in June within the same factory, suggesting that the large outbreak was seeded by cases related to the initial infection cluster.

The results indicated that climate conditions, fresh air exchange rates, and airflow, were factors that can promote efficient spread of SARS-CoV-2 over long distances, but that shared accommodation and transport played a smaller role, at least during the initial phase of the outbreak. Earlier studies already suggested that tiny droplets called aerosols may be responsible for so-called super spreading events where a single source transmits the virus to a large number of individuals. Whereas larger droplets typically travel no farther than two meters, aerosols can stay in the air for prolonged periods of time and may deliver infectious viral particles over substantially greater distances, especially in indoor settings.

The recurrent emergence of such outbreaks suggests that employees in meat or fish processing facilities should be frequently and systematically screened to prevent future SARS-CoV-2 outbreaks. Furthermore, immediate action needs to be taken to quarantine all workers in a radius around an infected individual that may significantly exceed two meters.

Additional studies are required to determine the most important workplace parameters that may be altered to lower infection risk, but optimization of airflow and ventilation conditions are clearly indicated.



Journal reference:

Günther, T., et al. (2020) SARS‐CoV‐2 outbreak investigation in a German meat processing plant. EMBO Molecular Medicine.
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

SARS-CoV-2 is mainly spread in households and household-like settings

10/27/20 ... tings.aspx

Ten months into the coronavirus disease (COVID-19) pandemic, health experts have a good understanding of how the virus spreads. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreads through respiratory droplets and aerosols and enters the body through the mouth, nose, and eyes.

The virus has spread across the globe, causing epidemics that range from quickly controlled local outbreaks, such as those seen in New Zealand to large ones that have affected millions of people, akin to the one happening in the United States.

Since the start of the pandemic, many studies and debates have highlighted the relative importance of various transmission routes, the roles of presymptomatic and asymptomatic spread, and the susceptibility and transmissibility of specific age groups.

Now, a new article published in the journal Science provides insights on the engines of SARS-CoV-2 spread.

Households and other residential settings

The authors of the report from Johns Hopkins School of Medicine and Johns Hopkins Bloomberg School of Public Health said that a majority of SARS-CoV-2 infections happen within households and other residential settings, including nursing homes. The virus usually spreads through close contact with infected individuals, especially those that happen for long periods. Most people live with others, and household contacts include many forms of high-intensity, close, and long-duration interaction.

For instance, a study in South Korea has shown that of the over 59,000 case contacts, household contacts are six times more likely to contract the virus than other close contacts. Further, household contacts accounted for more than half of identified secondary infections in the same study.

The research team also found that even among close contacts, some people are at a higher risk of infection. For instance, spouses are more than twice likely to be infected as other household members, while those who develop symptoms are more likely to transmit the virus. The elderly may face the risk of infection from younger family members who work outside the home.

Just like in families that live together, other residential settings such as prison, home care facilities, and dormitories are high-risk areas for COVID-19 spread. About 66 percent of residents were infected in homeless shelters, 62 percent in a nursing home, and 80 percent in a prison area.


Although transmission is more common in households and residences, community transmission also plays a significant role in the COVID-19 spread.

Many people with COVID-19 may be presymptomatic or those without symptoms at the start of the infection but develops them later on, or asymptomatic, those who never develop any symptom at all.

“Viral loads appear to be similar between asymptomatic and symptomatic patients, although the implications for infectiousness are unclear. People experiencing symptoms may self-isolate or seek medical care, but those with no or mild symptoms may continue to circulate in the community,” the researchers wrote.

Dubbed as superspreaders, these people may transmit the virus to others without them knowing. It is more difficult to spot these people and trace who were their close contacts.

Meanwhile, superspreading events and transmission-amplifying settings contribute to the rapid spread of the virus.

“Both superspreading events and transmission-amplifying settings are part of a more general phenomenon: overdispersion in transmission. Overdispersion means that there is more variation than expected if cases exhibit homogeneity in transmissibility and number of contacts; hence, a small number of individuals are responsible for the majority of infections,” the team added.

As the pandemic evolves, more and more knowledge is gained on how the virus spreads. However, there is much more to learn about its behavior, especially as the winter season fast approaches the northern hemisphere. A better understanding of how the engines of transmission interact is vital for implementing sound mitigation strategies to combat the raging pandemic, which has now infected over 43.4 million people worldwide.


Park, Y.J., Choe, Y.J., Park, S.Y. et al. (2020). Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020. Emerging Infectious Diseases.
COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU) - ... 7b48e9ecf6

Journal reference:

Lee, E., Wada, N., Grabowski, M., Gurley, E., Lessler, J., et al. (2020). The engines of SARS-CoV-2 spread. Science.
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Bigger households associated with greater odds of SARS-CoV-2 transmission

10/27/20 ... ssion.aspx

As the coronavirus disease (COVID-19) pandemic continues to spread across the globe, more information emerges on how the virus spreads. Household transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been flagged as one of the major sources of the spread of COVID-19.

The secondary attack rates among household contacts are estimated to be five to ten times higher than among non-household contacts. However, it is unclear who among the household members are more likely to spread the virus.

Now, a team of researchers at Public Health Ontario and Sunnybrook Research Institute aimed to determine the factors that drive household transmission of the coronavirus. Specifically, the researchers wanted to compare the characteristics of cases in households with secondary transmission than those who did not.

The team found that longer testing delays and being male were tied to a higher risk of secondary household transmission. Also, households with more family members are more likely to experience the COVID-19 spread.

The study

The study, published on the preprint server medRxiv*, highlights how household transmission contributes to the growing number of coronavirus cases, which has now topped 43.89 million worldwide.

The team used address matching to identify all households with confirmed SARS-CoV-2 infections from Ontario in Canada from January to July to arrive at the study findings. The researchers compared the characteristics of cases in households that had secondary transmission to those that did not. To obtain the data, they used the provincial reportable disease systems entered by local public health units.

A secondary transmission happens when cases occur 1 – 14 days after the first person who had the coronavirus was identified. The team used the symptom onset date or the specimen collection date. Further, they also considered a wide range of individual-level and neighborhood-level covariates in the study, tied to household transmission.

Study findings

Overall, there were more than 38,000 confirmed COVID-19 cases reported in Ontario. After removing some cases based on the inclusion criteria, the team had more than 26,000 cases living in private households. From these, more than 18,000 cases were from households with no secondary transmission, and more than 7,900 cases were from households with the secondary transmission.

The team has found that longer testing delays and being male contribute to a higher risk of secondary transmission in the house or apartment. On the other hand, being a healthcare worker or linked to a known outbreak has been tied to lower household transmission chances.

The team also found that neighborhoods with a larger average economic family size and a higher proportion of people living in a room were tied to greater household transmission odds. This means that the more people living in a home, the higher the risk of a COVID-19 outbreak in the household.

“Our findings of higher odds of household transmission among neighborhoods with a higher proportion of multiple persons per room and multi-family households may support this hypothesis, and our association with economic family size may be capturing aspects of household crowding at the neighborhood,” the team explained.

Household transmission plays a pivotal role in the spread of SARS-CoV-2. The study recommends that it is essential for people to get tested immediately or as soon as symptoms appear. This way, they will take precautions to protect the other members of the family.

“Ideally, individuals should be tested on the day of symptom onset, as even a 1-day delay was associated with increased odds of secondary transmission. Additionally, if cases are living with other individuals, it may also be important to try to isolate in a room alone or outside the home, if possible,” the researchers said.

These mitigation strategies may be considered by public health officials to combat household transmission. Further studies should be done to focus on the role of children and the youth in household transmission.

The coronavirus pandemic has now killed more than 1.16 million people. The United States remains the hardest-hit country, reporting more than 8.77 million cases, followed by India, with a staggering 7.94 million people.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU) - ... 7b48e9ecf6

Journal reference:

Paul, L., Daneman, N., Brown, K., Johnson, J. et al. (2020). Characteristics associated with the household transmission of SARS-CoV-2 in Ontario, Canada. medRxiv. ... 20217802v1
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Mouth may be primary route of SARS-CoV-2 infection and transmission

10/29/20 ... ssion.aspx

The viral transmission underlying the current COVID-19 pandemic has been a matter of intense investigation. According to the World Health Organization (WHO), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a respiratory virus, and transmission is by respiratory droplets and aerosols from infected individuals. A new study published on the preprint server medRxiv* in October 2020 shows that the virus also multiplies robustly in the oral cavity, indicating that saliva plays a role in viral transmission.

It is now accepted that breathing, singing, coughing, and sneezing are linked to SARS-CoV-2l transmission. All of these involve air passing through the mouth, but most research has explored infectious particles' movement from the lungs and the nose to the outside to possibly infect others.

Among 40 studies, including over 10,000 COVID-19 patients, however, there was a range of oral manifestations, such as ageusia, dryness of mouth, and blisters on the mucosal lining, in half of all cases.

Saliva contains viral RNA, and as a result, is being employed as a diagnostic test sample. However, if the oral cavity and associated salivary glands transmit the virus through saliva to the lung and the gut, saliva could also be of importance in carrying the virus to others.

Susceptibility of Oral Tissues

Therefore, the current study sought to examine the infection and replication of the virus in oral tissues, including the mucous membrane and the salivary glands. Viral entry depends on host receptors like ACE2 and TMPRSS2, which have poorly described but variable expression patterns in oral tissues. The oral cavity contains a wide variety of cells adapted to feeding, digestion, and speech.

Heterogeneous Cell Types

The researchers first generated a human oral single-cell RNA sequencing atlas, the first-ever, to help predict which cell types might promote SARS-CoV-2 infection. They found that in just the minor salivary glands (SGs) and the gums, there were 50 cell types.

The former had epithelial types belonging to the serous and mucous acini, salivary ducts, myoepithelial cells, and glia, besides ionocytes, fibroblasts, endothelial, and smooth muscle cells. There were also types of immune cells, including plasma cells and B cells, T cells, and macrophages. The gums also showed dendritic and other immune cell types and various types of epithelium.

Viral Entry Receptor Expression

They then used in situ hybridization (ISH) to examine the pattern of ACE2 and TMPRSS2 expression in various epithelial cell types in the SGs and mucosal cells. Based on this, they predicted that SARS-CoV-2 infection could occur in multiple epithelial types, especially the SG ducts and acini, and the uppermost layers of the mucosal epithelium.

This was confirmed on autopsy and outpatient samples of the oral and oropharyngeal mucosa, using ISH and confirmatory polymerase chain reaction (PCR) testing for viral RNA. This proved that the mucosa are sites of SARS-CoV-2 infection, with SGs being susceptible to infection. The shed epithelium could provide potential routes for the virus to spread to other parts of the body through the saliva.

Two SG responses are possible, the first being a response to SARS-CoV-2 infection by shedding the infected cells and reducing gene activity involved in viral protein transcription. The other may allow the virus to replicate in a sheltered environment, leading to persistent and symptomatic infection.

Oral Infection, Shedding in Saliva, and Symptoms

The researchers also carried out a prospective study in an outpatient cohort, using nasopharyngeal mucosa and saliva samples. They looked for correlations between the viral burden in saliva, viral RNA in the shed oral epithelial cells, and the presence of symptoms suspicious of COVID-19.

They found that some patients took more than two months to clear the virus from saliva and nasopharyngeal samples. Asymptomatic subjects also carry the virus for long periods of time. In some cases, the nasopharyngeal samples were negative for the virus, while saliva continued to be positive, indicating sustained viral shedding from either infected SGs or infected epithelial cells.

Finally, the detection of salivary SARS-CoV-2 RNA predicted anosmia and ageusia associated with a high viral load and epithelial cell infection. The use of masks decreased expelled salivary droplets by a factor of over 10. Further study will show if this is equivalent to reduced viral RNA as well.


Overall, this study demonstrates the susceptibility of the oral mucosa and SGs to this virus and the presence of actual infection. Transmission of the virus via saliva will require public health measures to block salivary dispersion.

Moreover, the integrated oral human atlas showed the broad susceptibility of minor SGs to SARS-CoV-2. These glands are spread over the tongue, palate, and mucosa, all of which are "hotspots for SARS-CoV-2 infection." This correlates well with and may help explain why COVID-19 patients often lose their sense of taste and complain of a dry mouth.

The occurrence of asymptomatic but productive infection at most of these sites could also explain why silent spread occurs so frequently in COVID-19. Again, comparison with mouse oral cavity single-cell data showed that the expression of both ACE2 and TMPRSS2 increased as cells in the epithelium moved from the bottom towards the top, poised to eventually shed into the saliva. This would favor and explain asymptomatic COVID-19 since shed cells do not produce any specific symptoms.

On the other hand, these infected epithelial cells can induce a strong local immune response in both the gut and the mucosa, with antibodies being secreted by the oral mucosa and the SGs. This corresponds to the observed link between the presence of oral infection and a robust antibody response in saliva.

The authors conclude: “The discovery of an oral source of infection and replication in the SG as well as the natural conduit for viral spread via saliva establishes the possibility of two infection axes in COVID-19.”

Future Directions

The study raises the need for testing both nasopharyngeal and oral samples to assess the spread of SARS-CoV-2. Secondly, the authors point out the possibility that the virus spreads not from the nose to the mouth through respiratory mucus but from the mouth, which is infected via fomites or droplets. Thirdly, the above question also leads to further confusion as to whether the route of primary infection affects the clinical severity and the host immune response.

Daily testing using both nasopharyngeal swabs and salivary testing will be needed to help answer these questions. This study's importance is providing a proper understanding of asymptomatic spread, which has been the bane of all containment efforts, is obvious. The findings also support the relevance of universal hand hygiene, face mask use, and social distancing to prevent transmission via salivary droplets and aerosols and fomites contaminated by saliva.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

Byrd, K. M. et al. (2020). Integrated Single-Cell Atlases Reveal an Oral SARS-CoV-2 Infection and Transmission Axis. medRxiv preprint. doi: ... 20219089v1
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Researchers track the flight trajectory of airborne cough droplets

11/3/20 ... plets.aspx

The ongoing COVID-19 pandemic has led many researchers to study airborne droplet transmission in different conditions and environments. The latest studies are starting to incorporate important aspects of fluid physics to deepen our understanding of viral transmission.

In a new paper in Physics of Fluids, by AIP Publishing, researchers from A*STAR's Institute of High Performance Computing conducted a numerical study on droplet dispersion using high fidelity air flow simulation. The scientists found a single 100-micrometer cough droplet under wind speed of 2 meters per second can travel up to 6.6 meters and even further under dry air conditions due to droplet evaporation.

" In addition to wearing a mask, we found social distancing to be generally effective, as droplet deposition is shown to be reduced on a person who is at least 1 meter from the cough."

- Fong Yew Leong, Author

The researchers used computational tools to solve complex mathematical formulations representing air flow and the airborne cough droplets around human bodies at various wind speeds and when impacted by other environmental factors. They also assessed the deposition profile on a person at a certain proximity.

A typical cough emits thousands of droplets across a wide size range. The scientists found large droplets settled on the ground quickly due to gravity but could be projected 1 meter by the cough jet even without wind. Medium-sized droplets could evaporate into smaller droplets, which are lighter and more easily borne by the wind, and these traveled further.

The researchers offer a more detailed picture of droplet dispersion as they incorporated the biological considerations of the virus, such as the nonvolatile content in droplet evaporation, into the modelling of the airborne dispersion of droplets.

"An evaporating droplet retains the nonvolatile viral content, so the viral loading is effectively increased," said author Hongying Li. "This means that evaporated droplets that become aerosols are more susceptible to be inhaled deep into the lung, which causes infection lower down the respiratory tract, than larger unevaporated droplets."

These findings are also greatly dependent on the environmental conditions, such as wind speed, humidity levels, and ambient air temperature, and based on assumptions made from existing scientific literature on the viability of the COVID-19 virus.

While this research focused on outdoor airborne transmission in a tropical context, the scientists plan to apply their findings to assess risk in indoor and outdoor settings where crowds gather, such as conference halls or amphitheaters. The research could also be applied to designing environments that optimize comfort and safety, such as hospital rooms that account for indoor airflow and airborne pathogen transmission.


American Institute of Physics

Journal reference:

Li, H., et al. (2020) Dispersion of evaporating cough droplets in tropical outdoor environment. Physics of Fluids.
Posts: 2310
Joined: Fri Jun 26, 2020 5:22 am

Aerosolized Transmission

Post by trader32176 »

Dose of Coronavirus, Timing Matters for Infection

11/5/20 ... nfection#1

THURSDAY, Nov. 5, 2020 (HealthDay News) -- How likely you are to become infected with coronavirus can depend on how much virus you inhale, where those particles land in your respiratory tract, and even the weather, researchers report.

Researchers from many institutions are working on a National Science Foundation-funded project to develop a mask with a reusable respirator that captures and kills the COVID-19 virus.

As part of that effort, Saikat Basu, an assistant professor at South Dakota State University's Department of Mechanical Engineering, has developed a model that uses breathing rates to track the droplet sizes that are likely to reach vulnerable areas of the respiratory tract.

"To become infected, you must first inhale the virus, so inhalation patterns are important," Basu explained in a university news release.

Also important is wearing masks. A cell culture study from the University of North Carolina found that the upper part of the throat behind the nasal passages and above the esophagus and voice box -- an area known as the nasopharynx -- is the most accessible seeding zone for the virus.

In his study, Basu used digital models to simulate inhalation rates in healthy adults. He reported that droplet sizes most likely to reach that zone were larger than expected.

"Most masks would block out these droplet sizes, so wearing a mask is very useful," Basu said. "These are also the droplet sizes that we need to make sure our new respirator design captures."

The data could also be useful in developing inhaled antivirals and intranasal vaccines that reach this initial infection site.

One negative discovery is that virus-carrying droplets can dehydrate in the air, increasing the concentration of virus particles and their potential to cause disease. This could have an impact on COVID-19 transmission this winter, when the humidity drops and triggers a faster rate of dehydration of the droplets.

"The droplets being inhaled after dehydration in the external air carry a larger viral load," Basu noted.

To estimate the threshold for infection, Basu looked at reports on a May superspreader event among a choral group of 61 people in Skagit Valley, Wash., where one symptomatic person transmitted COVID-19 to 52 other members.

To estimate probability that a droplet would contain at least one virus particle, Basu used a study on the amount of virus in the sputum and mucus of COVID-19 patients and accounted for dehydration. He conservatively estimated about 300 virus particles as the threshold for infection. Typically, an inhaled viral infection requires 1,950 to 3,000 virus particles.

"The fact that the number of virus particles needed to launch the infection is in the range of hundreds is very remarkable, and shows how contagious this particular virus is," Basu said.

The results from the droplet inhalation modeling were screened by the scientific team at medRxiv. The corresponding research manuscript is undergoing peer review at the journal PLOS One.
Post Reply