Aerosolized Transmission

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Re: Aerosolized Transmission

Post by trader32176 »

NO SHOUTING: California theme parks ban people from screaming in rides to prevent coronavirus spread

3/19/21 ... rides.html

Theme parks in California will limit patrons’ screaming or shouting on rides to curb the spread of COVID-19. A union of amusement parks in the state proposed the measure in a list of actions they would take to safely reopen these leisure facilities in line with a state blueprint.

The California Attractions and Parks Association (CAPA) shared a list of steps its member amusement parks would be taking to safely reopen their properties to the public. It drafted the list with the hope of better following the state’s blueprint for determining COVID-19 risk. According to CAPA, member parks “have been busy planning and preparing to implement their own site-specific plans for reopening.”

Theme parks to limit activities known to cause the spread of COVID-19

CAPA’s plan detailed how amusement parks and attractions can reopen “in limited capacity with the proper modifications.” Limiting activities and environments that are known to cause increased COVID-19 transmission and require people to raise their voices was among the points indicated in the plan.

To address concerns about the virus’ spread, amusement park operators will require the use of face masks or face coverings for park ride passengers. Seat loading patterns on rides will also be modified “to mitigate the effects of shouting.” CAPA also remarked that guests ought to “generally face in one direction” on rides to minimize excess noise. The association also added it will only sit people from the same party for various rides and attractions to prevent mixing and mingling of amusement park visitors. CAPA explained that amusement parks “do not encourage congregations” as families stay within their own household group when visiting.

Furthermore, the CAPA list also says that amusement parks will provide designated eating and drinking areas where people can remove their masks. Eating on the go will no longer be allowed as guests will be required to wear face coverings while walking around.

New regulations in line with theme park re-openings in California

CAPA published the reopening action plan as a spike in coronavirus cases in the winter rapidly tapered off. California officials announced in early March that reopening criteria for theme parks and outdoor stadiums would be relaxed starting April 1.

Theme parks will only be allowed to re-open if the county they are located in drops below California’s restrictive coronavirus tier. They will also be permitted to re-open albeit initially at 15 percent capacity, and the parks will be open only to California residents.

Disneyland was among the theme parks in the state aiming to reopen soon. The “happiest place on Earth” has joined other amusement park operators and local officials in pressuring state authorities to permit swift re-opening. Disney CEO Bob Chapek said the previous week that the park was targeting a late April 2021 re-opening after the state eased COVID-19 restrictions.

The theme park in Anaheim, located near Los Angeles, has been closed for almost exactly a year – while other Disney resorts worldwide have re-opened their doors. Based on previous guidance, theme parks would be among the last places to re-open in California. But the projection has not dissuaded Chapek. “Here in California, we’re encouraged by the positive trends we’re seeing. [We’re] hopeful they’ll continue to improve and we’ll be able to reopen our parks to guests with limited capacity by late April,” he said. (Related: Disneyland converted into mass COVID-19 vaccination site.)

The Disney CEO cautioned that the park could not reopen on April 1, the date originally eyed for resumption. He explained that it would take time to recall more than 10,000 furloughed staff members and to retrain them in pandemic safety measures. Chapek added that a precise opening date would be confirmed “in the coming weeks.” (Related: Disney to lay off 28,000 workers in belt-tightening move amid coronavirus pandemic.)

Soon enough, Disneyland posted on its Twitter account that it would reopen its doors on April 30. In a March 17 tweet, the park said it plans to officially reopen with limited capacity, and only for California residents.
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Re: Aerosolized Transmission

Post by trader32176 »

Thermo Fisher Scientific launches in-air SARS-CoV-2 surveillance solution

4/8/21 ... ution.aspx

Thermo Fisher Scientific Inc., the world leader in serving science, today announced the launch of the Thermo Scientific AerosolSense Sampler, a new surveillance solution designed to deliver fast and highly reliable insight into the presence of in-air pathogens, including SARS-CoV-2.

Individual testing will continue to be a cornerstone in the COVID-19 pandemic response because it enables and informs clinical diagnoses, patient triage and treatment decisions. As society returns to pre-pandemic activities, expanded and complementary monitoring of environments will be key in providing useful insights into virus presence. The AerosolSense Sampler is the next step in providing institutions with highly reliable information to help keep their employees and the public safe.

The AerosolSense Sampler is an in-air pathogen surveillance solution, which collects representative aerosol samples of ambient air and traps in-air pathogens on a collection substrate. The sample can be readily analyzed through subsequent laboratory testing using polymerase chain reaction (PCR) methodology. Confirming the presence of pathogens like SARS-CoV-2 in a space during a known time interval enables decision makers in hospitals and other indoor facilities to take actions to protect their employees and provide the public with confidence.

" Such factors as emerging variants, semi-vaccinated populations and varying levels of compliance with COVID-19 personal safety protocols, continue to pose risks to a society looking to return to life as it was before the pandemic. It is important that easy-to-use, highly reliable solutions be available to allow hospitals, nursing homes, schools, businesses and government institutions to identify the presence of in-air pathogens quickly, so safety protocols can be put into action, validated, or strengthened."

- Mark Stevenson, Executive vice president and chief operating officer, Thermo Fisher Scientific

Dr. John Broach, assistant professor of Emergency Medicine at the University of Massachusetts and an early user of the AerosolSense Sampler said, "Monitoring the efficacy of infection control practices is invaluable to protecting health care providers on the frontlines. Combatting COVID-19 is a multi-front battle, and this surveillance solution can be implemented seamlessly within institutions to alert them to the presence of SARS-CoV-2, so that they can take appropriate steps to prevent its spread."

Thermo Fisher designed the AerosolSense Sampler to capture a wide variety of in-air pathogens and has specifically validated it for the SARS-CoV-2 pathogen.


Thermo Fisher Scientific Inc.
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Re: Aerosolized Transmission

Post by trader32176 »

Researchers assess SARS-CoV-2 transmission risk during air travel

4/15/21 ... study.aspx

A team of scientists from the United States recently conducted a meta-analysis to estimate the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during air travel. The findings reveal that even with SARS-CoV-2-infected persons onboard, the risk of viral transmission is low inside an aircraft. The study is currently available on the medRxiv* preprint server.


As of April 15, 2021, globally, there have been 136 million confirmed cases of coronavirus disease 2019 (COVID-19), including 2.9 million deaths, registered to the World Health Organization (WHO). At the initial phase of the pandemic, strict control measures applied to control the viral transmission have severely impacted the socioeconomic status of many countries globally. Because of national and international travel restrictions, the aviation industries have faced an almost 95% drop in passenger numbers during the initial phase of the pandemic.

As the pandemic progresses, the aviation-related services of many countries have been resumed to boost the global economy. This gives rise to global concerns about the risk of SARS-CoV-2 transmission among passengers traveling by air across the globe.

Viral transmission due to air travel can occur in two ways. A passenger with SARS-CoV-2 infection traveling via aircraft to a new location can transmit COVID-19 either on the ground or inside the aircraft.

In the current study, the scientists estimated the risk of SARS-CoV-2 transmission from an infected person to fellow passengers inside an aircraft.

Study design

The scientists conducted a systemic review of the present literature to estimate the number of index patients and secondary COVID-19 cases related to air travel between January 2020 and September 2020. An index patient refers to a passenger who was infected before air travel. A secondary COVID-19 case refers to the passenger who became infected from the index patient during air travel.

Because the primary focus of most of the published studies was infected passengers, the current risk estimation was limited to flights with index patients and did not involve the transmission risks among aircrew, ground crews, and airport staff.

The scientists estimated the risk of viral transmission using a quantitative approach that considered secondary cases and the total number of passengers inside an aircraft. The data collected from published literature were corrected for known data limitations, such as asymptomatic and underreported COVID-19 cases. Moreover, because COVID-19 testing and reporting processes vary across different locations/countries, uncertainties were also included in the risk calculation to obtain the most accurate risk estimation.

Important observations

According to the study findings, about 1.4 billion passengers traveled by air between January 2020 and September 2020. Among all air travelers, 2,866 were identified as index patients, and 44 were identified as potential secondary COVID-19 cases.

For estimating the risk of transmission during air travel, the scientists hypothesized that all possible transmissions occurred inside the aircraft cabin; however, they mentioned that in some cases, the transmission could have occurred elsewhere, such as in the airport.

Available literature on in-flight transmission

In a London-Hanoi flight on March 2, 2020, 15 secondary COVID-19 cases were identified. However, based on the duration between flight arrival and a positive SARS-CoV-2 test result, the scientists hypothesized that all these passengers were infected after the completion of air travel.

Furthermore, in a Singapore to Hangzhou, China flight on January 24, 2020, 15 index patients and only a single secondary COVID-19 case were identified. With further analysis, the scientists observed that except for eating food and drinking water, all 16 passengers wore masks throughout the air travel. However, the secondary case did not wear a mask properly when sitting in an unassigned seat surrounded by infected symptomatic passengers.

Estimated risk of in-flight transmission

By including all data correction factors in the calculations, the scientists estimated that the risk of SARS-CoV-2 transmission inside an aircraft cabin is 1 in 1.7 million. Furthermore, using the uncertainty estimates of publicly available literature, they estimated that the risk of in-flight transmission ranges from 1 case in every 712,000 passengers to 1 case in every 8 million passengers.

Study significance

The study reveals that the risk of SARS-CoV-2 transmission inside an aircraft cabin is as low as 1 case in 1.7 million passengers. In other words, the study findings indicate that even with index patients onboard, the overall risk of acquiring secondary infection is low during air travel.

Improved environmental control measures inside an aircraft cabin, such as high airflow, high-quality air purification, and seating arrangements, are believed to play a significant role in reducing the risk of viral transmission among passengers.

*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:

Pang JK. 2021. Probability and Estimated Risk of SARS-CoV-2 Transmission in the Air Travel System: A Systemic Review and Meta-Analysis. MedRxiv. doi:, ... 21255171v1
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Re: Aerosolized Transmission

Post by trader32176 »

Future attempts to reduce Covid-19 spread should focus on tackling airborne transmission

4/15/21 ... ssion.aspx

Any future attempts to reduce the spread of covid-19 should be focused on tackling close airborne transmission of the virus which is considered to be the primary route for its circulation, according to experts in an editorial published in The BMJ.

Respiratory experts argue that it is now clear that covid-19 (SARS-CoV-2) is most likely to transmit between people at close range through inhalation rather than through contact with surfaces or longer range airborne routes, although those routes can also be responsible.

The covid-19 pandemic has helped to redefine airborne transmission of viruses, say the experts from the universities of Leicester, Edinburgh Napier and Hong Kong, Virginia Tech, and NHS Lanarkshire, Edinburgh.

There has been some confusion over precise definitions of air transmissions of infections from the last century in which the difference between “droplet” “airborne,” and “droplet nuclei” transmission have led to misunderstandings over the physical behavior of these particles, they say.

What is important to know, they claim, is that if a person can inhale particles, regardless of their size or name, they are breathing in aerosols. And while this can happen at long range, it is more likely to happen when being close to someone because the aerosols between two people are much more concentrated at short range, similar to being close to someone who is smoking.

People infected with SARS-CoV-2 produce many small respiratory particles full of the virus as they exhale. Some of these will be inhaled almost immediately by those within a typical conversational “short range” distance of less than one meter, say the experts, while the remainder will disperse over longer distances to be inhaled by others further away – more than two metres.

The well-known and often used preventative steps of wearing masks, keeping your distance, and reducing indoor occupancy all help to reduce the usual routes of transmission, whether through direct contact with surfaces or droplets, or from inhaling aerosols, they say.

However, they argue that a crucial difference is the need for added emphasis on ventilation because the tiniest suspended particles can remain in the air for hours and these are an important route of transmission.

Therefore measures to ensure that air is replaced or cleaned are all the more important, meaning opening windows, installing or upgrading heating, ventilation, and use of air conditioning systems.

In addition, the quality of masks is important to ensure effective protection against inhaled aerosols. Masks usually prevent large droplets from landing on covered areas of the face but tiny airborne particles can find their way around any gaps.

High quality masks with high filtration efficiency and a good fit are, therefore, important, they say.

Efforts to improve the quality of indoor air through better ventilation will bring other benefits, they add, such as reduced sick leave for other respiratory viruses and other environmentally related complaints including allergies and sick building syndrome.

If companies experienced less absenteeism with its impact on productivity, this could save them significant costs which would offset the expense of upgrading their ventilation systems.

The experts conclude: “Covid-19 may well become seasonal, and we will have to live with it as we do with influenza. So governments and health leaders should heed the science and focus their efforts on airborne transmission.

“Safer indoor environments are required, not only to protect unvaccinated people and those for whom vaccines fail, but also to deter vaccine resistant variants or novel airborne threats that may appear at any time.

“Improving indoor ventilation and air quality, particularly in healthcare, work, and educational environments, will help all of us to stay safe, now and in the future.”



Journal reference:

Tang, J.W., et al. (2021) Covid-19 has redefined airborne transmission. BMJ.
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Re: Aerosolized Transmission

Post by trader32176 »

A new approach to estimate the risks of exposure to COVID-19 under different indoor settings

4/16/21 ... tings.aspx

Two MIT professors have proposed a new approach to estimating the risks of exposure to Covid-19 under different indoor settings.

The guideline they developed suggests a limit for exposure time, based on the number of people, the size of the space, the kinds of activity, whether masks are worn, and the ventilation and filtration rates. Their model offers a detailed, physics-based guideline for policymakers, businesses, schools, and individuals trying to gauge their own risks.

The guideline, appearing this week in the journal PNAS, was developed by Martin .Z. Bazant, professor of chemical engineering and applied mathematics, and John W. M. Bush, professor of applied mathematics. They stress that one key feature of their model, which has received less attention in existing public-health policies, is providing a specific limit for the amount of time a person spends in a given setting.

Their analysis is based on the fact that in enclosed spaces, tiny airborne pathogen-bearing droplets emitted by people as they talk, cough, sneeze, sing, or eat will tend to float in the air for long periods and to be well-mixed throughout the space by air currents.

There is now overwhelming evidence, they say, that such airborne transmission plays a major role in the spread of Covid-19. Bush says the study was initially motivated early last year by their concern that many decisions about policies were being guided primarily by the "6-foot rule," which doesn't adequately address airborne transmission in indoor spaces.

Using a strictly quantitative approach based on the best available data, the model produces an estimate of how long, on average, it would take for one person to become infected with the SARS-CoV-2 virus if an infected person entered the space, based on the key set of variables defining a given indoor situation.

Rather than a simple yes or no answer about whether a given setting or activity is safe, it provides a guide as to just how long a person could safely expect to engage in that activity, whether it be a few minutes in a store, an hour in a restaurant, or several hours a day in an office or classroom, for example.

" As scientists, we've tried to be very thoughtful and only go with what we see as hard data. We've really tried to just stick to things we can carefully justify. We think our study is the most rigorous study of this type to date. While new data are appearing every day, and many uncertainties remain about the SARS-CoV-2 virus' transmission. We feel confident that we've made conservative choices at every point."

- Martin .Z. Bazant, Professor of Chemical Engineering and Applied Mathematics, Massachusetts Institute of Technology

Bush adds: "It's a quickly moving field. We submit a paper and the next day a dozen relevant papers come out, so we scramble to incorporate them. It's been like shooting at a moving target." For example, while their model was initially based on the transmissibility of the original strain of SARS-CoV-2 from epidemiological data on the best characterized early spreading events, they have since added a transmissibility parameter, which can be adjusted to account for the higher spreading rates of the new emerging variants. This adjustment is based on how any new strain's transmissibility compares to the original strain; for example, for the U.K. strain, which has been estimated to be 60 percent more transmissible than the original, this parameter would be set at 1.6.

One thing that's clear, they say, is that simple rules, based on distance or capacity limits on certain types of businesses, don't reflect the full picture of the risk in a given setting. In some cases that risk may be higher than those simple rules convey; in others it may be lower. To help people, whether policymakers or individuals, to make more comprehensive evaluations, the researchers teamed with app developer Kasim Khan to put together an open-access mobile app and website where users can enter specific details about a situation -- size of the space, number of people, type of ventilation, type of activity, mask wearing, and the transmissibility factor for the predominant strain in the area at the time -- and receive an estimate of how long it would take, under those circumstances, for one new person to catch the virus if an infected person enters the space.

The calculations were based on inferences made from various mass-spreading events, where detailed data were available about numbers of people and their age range, sizes of the enclosed spaces, kinds of activities (singing, eating, exercising, etc.), ventilation systems, mask wearing, the amount of time spent, and the resulting rates of infections. Events they studied included, for example, the Skagit Valley Chorale in Washington state, where 86 percent of the seniors present became infected at a two-hour choir practice

While their guideline is based on well-mixed air within a given space, the risk would be higher if someone is positioned directly within a focused jet of particles emitted by a sneeze or a shout, for example. But in general the assumption of well-mixed air indoors seems to be consistent with the data from actual spreading events, they say.

"When you look at this guideline for limiting cumulative exposure time, it takes in all of the parameters that you think should be there -- the number of people, the time spent in the space, the volume of the space, the air conditioning rate and so on," Bush says. "All of these things are kind of intuitive, but it's nice to see them appear in a single equation."

While the data on the crucial importance of airborne transmission has now become clear, Bazant says, public health organizations initially placed much more emphasis on handwashing and the cleaning of surfaces. Early in the pandemic, there was less appreciation for the importance of ventilation systems and the use of face masks, which can dramatically affect the safe levels of occupancy, he says.

"I'd like to use this work to establish the science of airborne transmission specifically for Covid-19, by just taking into account all factors, the available data, and the distribution of droplets for different kinds of activities," Bazant says. He hopes the information will help people make informed decisions for their own lives: "If you understand the science, you can do things differently in your own home and your own business and your own school."

Bush offers an example: "My mother is over 90 and lives in an elder care facility. Our model makes it clear that it's useful to wear a mask and open a window -- this is what you have in your control." He was alarmed that his mother was planning to attend an exercise class in the facility, thinking it would be OK because people would be 6 feet apart. As the new study shows, because of the number of people and the activity level, that would actually be a highly risky activity, he says.

Already, since they made the app available in October, Bazant says, they have had about half a million users. Their feedback helped the researchers refine the model further, he says. And it has already helped to influence some decisions about reopening of businesses, he adds.

For example, the owner of an indoor tennis facility in Washington state that had been shut down due to Covid restrictions says he was allowed to reopen in January, along with certain other low-occupancy sports facilities, based on an appeal he made based in large part on this guideline and on information from his participation in Bazant's online course on the physics of Covid-19 transmission.

Bazant says that in addition to recommending guidelines for specific spaces, the new tools also provide a way to assess the relative merits of different intervention strategies. For example, they found that while improved ventilation systems and face mask use make a big difference, air filtration systems have a relatively smaller effect on disease spread. And their study can provide guidance on just how much ventilation is needed to reach a particular level of safety, he says.

"Bazant and Bush have provided a valuable tool for estimating (among other things) the upper limit on time spent sharing the air space with others," says Howard Stone, a professor of mechanical and aerospace engineering at Princeton University who was not connected to this work. While such an analysis can only provide a rough estimate, he says the authors "describe this kind of order of magnitude of estimate as a means for helping others judge the situation they might be in and how to minimize their risk. This is particularly helpful since a detailed calculation for every possible space and set of parameters is not possible."


Massachusetts Institute of Technology

Journal reference:

Bazant, M. Z & Bush, J. W. M., et al. (2021) A guideline to limit indoor airborne transmission of COVID-19. Proceedings of the National Academy of Sciences.
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Re: Aerosolized Transmission

Post by trader32176 »

The CDC says empty middle seats reduce COVID-19 exposure on flights. Will airlines bring social distancing back?

4/15/21 ... 224517002/

Blocking middle seats on airplanes reduces the risk of COVID-19 exposure, according to a study released Wednesday by the Centers for Disease Control and Prevention.

The research, done in conjunction with Kansas State University, found a 23% to 57% reduction in exposure to "viable'' virus particles when middle seats are vacant.

The conclusion: "Physical distancing of airplane passengers, including through policies such as middle seat vacancy, could provide additional reductions in risk for exposure to SARS-CoV-2 on aircraft.''

Airlines have abandoned the pandemic practice of blocking seats to maintain social distance between travelers.

Delta Air Lines is the only U.S. carrier still blocking middle seats in economy, and that practice will end May 1. Southwest stopped blocking seats Dec. 1.

United Airlines CEO Scott Kirby has repeatedly said there is no way to keep passengers 6 feet apart on a plane, and chief communication officer Josh Earnest said last summer that blocking seats is a PR strategy, not a safety strategy.

"The CDC just dropped a bombshell on the airline industry,'' said Robert Glatter, an emergency room physician at Lenox Hill Hospital in New York. "That's really what this report is.''

Delta Air Lines CEO Ed Bastian dismissed the results of the study in an appearance on CNBC early Thursday and said it will not change the airline's plans to start filling middle seats again in May.

"This study was based on 2017 data, so it doesn’t take into account any of the safety protocols that we’ve implemented, including masking, the electrostatic spraying (of planes), the cleanliness of the surfaces.''

With rising vaccination rates and strong travel demand, Bastian said the airline's experts say it's "absolutely safe to sit in that middle seat,'' he said.

On Wednesday, airlines deferred comment on the CDC study to their trade group, Airlines for America.

The group's statement did not address the study but reiterated that airlines have a host of measures to prevent virus transmission on planes, including hospital-grade ventilation systems, strict face mask requirements, preflight health forms and intensified cleaning of planes.

The group pointed to Harvard research, paid for in part by the airline industry, that concluded that the ventilation on planes, together with other measures, reduces the possibility of exposure to COVID-19 to a point where it "effectively counters the proximity travelers are subject to during flights.”

COVID-19 exposure on flights: More common than you think

The bottom line for travelers: Don't expect airlines to resume blocking seats or, in the case of Delta, to keep blocking them. (The CDC never required social distancing on planes. Airlines started the practice to give travelers confidence to book.)

Airlines lost billions in 2020 and are doing everything they can to fill their planes as travel resumes. On Easter Sunday and the following day, Delta temporarily lifted its middle seat block to rebook travelers stranded by flight cancellations caused by staffing issues and other factors.

Domestic travel is rebounding strongly: Passenger counts at U.S. airports have topped 1 million every day since March 10. The number of travelers had fallen below 100,000 a year ago and didn't top a million again until October.

Bookings got a boost this month when the CDC said vaccinated travelers can resume travel at low risk.

Delta estimates it lost $100 million to $150 million in revenue by blocking middle seats in March, president Glen Hauenstein said on the airline's earnings conference call Thursday.
CDC middle seat study: Mask use not included

The data for the social distancing study was collected before the pandemic began, so the effects of mandatory airline passenger mask use on COVID-19 exposure were not measured.

The CDC said the fact that mannequins in the study weren't wearing masks does not negate the findings, because the study measured aerosol exposure on the plane, and masks are "more effective at reducing fomite (objects such as clothes that might carry infection) and droplet exposures than aerosol (airborne) exposures.''

Glatter said the reduction in COVID-19 exposure without masks actually buttresses the CDC study's argument for keeping middle seats open.

"That's the reality of this: even without the masks they were able to reduce exposure, which is quite impressive,'' he said. "Imagine wearing a mask. That would be even more impactful.''

Glatter said the findings, and the fact that just one-quarter of Americans are vaccinated, suggest passengers should keep spreading out on planes until the pandemic is over.

"There's no question we should keep those middle seats open,'' he said.
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Re: Aerosolized Transmission

Post by trader32176 »

Covid-19 has redefined airborne transmission


Improving indoor ventilation and air quality will help us all to stay safe

Over a year into the covid-19 pandemic, we are still debating the role and importance of aerosol transmission for SARS-CoV-2, which receives only a cursory mention in some infection control guidelines.12

The confusion has emanated from traditional terminology introduced during the last century. This created poorly defined divisions between “droplet,” “airborne,” and “droplet nuclei” transmission, leading to misunderstandings over the physical behaviour of these particles.3 Essentially, if you can inhale particles—regardless of their size or name—you are breathing in aerosols. Although this can happen at long range, it is more likely when close to someone, as the aerosols between two people are much more concentrated at short range, rather like being close to someone who is smoking.4

People infected with SARS-CoV-2 produce many small respiratory particles laden with virus as they exhale. Some of these will be inhaled almost immediately by those within a typical conversational “short range” distance (<1 m), while the remainder disperse over longer distances to be inhaled by others further away (>2 m). Traditionalists will refer to the larger short range particles as droplets and the smaller long range particles as droplet nuclei, but they are all aerosols because they can be inhaled directly from the air.5

Why does it matter? For current infection control purposes, most of the time it doesn’t. Wearing masks, keeping your distance, and reducing indoor occupancy all impede the usual routes of transmission, whether through direct contact with surfaces or droplets, or from inhaling aerosols. One crucial difference, however, is the need for added emphasis on ventilation because the tiniest suspended particles can remain airborne for hours, and these constitute an important route of transmission.

If we accept that someone in an indoor environment can inhale enough virus to cause infection when more than 2 m away from the original source—even after the original source has left—then air replacement or air cleaning mechanisms become much more important.67 This means opening windows or installing or upgrading heating, ventilation, and air conditioning systems, as outlined in a recent WHO document.8 People are much more likely to become infected in a room with windows that can’t be opened or lacking any ventilation system.

A second crucial implication of airborne spread is that the quality of the mask matters for effective protection against inhaled aerosols. Masks usually impede large droplets from landing on covered areas of the face, and most are at least partially effective against inhalation of aerosols. However, both high filtration efficiency and a good fit are needed to enhance protection against aerosols because tiny airborne particles can find their way around any gaps between mask and face.910

If the virus is transmitted only through larger particles (droplets) that fall to the ground within a metre or so after exhalation, then mask fit would be less of a concern. As it is, healthcare workers wearing surgical masks have become infected without being involved in aerosol generating procedures.111213 As airborne spread of SARS-CoV-2 is fully recognised, our understanding of activities that generate aerosols will require further definition. Aerosol scientists have shown that even talking and breathing are aerosol generating procedures.141516

It is now clear that SARS-CoV-2 transmits mostly between people at close range through inhalation. This does not mean that transmission through contact with surfaces or that the longer range airborne route does not occur, but these routes of transmission are less important during brief everyday interactions over the usual 1 m conversational distance. In close range situations, people are much more likely to be exposed to the virus by inhaling it than by having it fly through the air in large droplets to land on their eyes, nostrils, or lips.17 The transmission of SARS-CoV-2 after touching surfaces is now considered to be relatively minimal.181920

Improved indoor air quality through better ventilation will bring other benefits, including reduced sick leave for other respiratory viruses and even environmentally related complaints such as allergies and sick building syndrome.2122 Less absenteeism—with its adverse effect on productivity—could save companies significant costs,23 which would offset the expense of upgrading their ventilation systems. Newer systems, including air cleaning and filtration technologies, are becoming ever more efficient.24

Covid-19 may well become seasonal, and we will have to live with it as we do with influenza.25 So governments and health leaders should heed the science and focus their efforts on airborne transmission. Safer indoor environments are required, not only to protect unvaccinated people and those for whom vaccines fail, but also to deter vaccine resistant variants or novel airborne threats that may appear at any time. Improving indoor ventilation and air quality, particularly in healthcare, work, and educational environments, will help all of us to stay safe, now and in the future.
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Re: Aerosolized Transmission

Post by trader32176 »

10 Signs Airborne Coronavirus Spread is What Matters

4/20/21 ... at-matters

April 20, 2021 -- The scientific evidence for airborne transmission of the coronavirus from different researchers all point in the same direction — that infectious aerosols are the principal means of person-to-person transmission.

Not that it's without controversy.

The science backing aerosol transmission "is clear-cut but it is not accepted in many circles," Trisha Greenhalgh, PhD, told Medscape.

"In particular, some in the evidence-based medicine movement and some infectious diseases clinicians are remarkably resistant to the evidence," added Greenhalgh, professor of primary care health sciences at the University of Oxford, northwest of London.

"The scientific evidence on spread from both near-field and far-field aerosols has been clear since early on in the pandemic, but there was resistance to acknowledging this in some circles, including the medical journals," Joseph G. Allen, DSc, said when asked to comment.

"This is the week the dam broke. Three new commentaries came out…in top medical journals — BMJ,The Lancet, JAMA— all making the same point that aerosols are the dominant mode of transmission," Allen, associate professor of exposure assessment science at the Harvard T.H. Chan School of Public Health in Boston, said..

Greenhalgh and colleagues point to an increase in COVID-19 cases in the aftermath of so-called "super-spreader" events, spread of the coronavirus to people across different hotel rooms, and the relatively lower transmission detected after outdoor events.

Top 10 Reasons

They outlined 10 scientific reasons backing airborne transmission in a commentary published online April 15 in The Lancet:

1) The dominance of airborne transmission is supported by transmission across long distances observed at super-spreader events.
2) These so-called long-range transmissions have been reported among rooms at COVID-19 quarantine hotels, where infected people never spent time in the same room.
3) Asymptomatic individuals account for an estimated 33% to 59% of coronavirus transmission, and these patients could spread the virus through speaking, which produces thousands of aerosol particles and few large droplets.
4) Transmission outdoors and in well-ventilated indoor spaces is lower than in enclosed spaces.
5) Infections have been reported in health care settings where there protective measures against large droplets (such as masks and personal protection equipment) but not aerosols.
6) Viable coronavirus has been detected in the air of hospital rooms and in the car of an infected person.
7) Investigators found coronavirus in hospital air filters and building ducts.
8) It's not just humans — infected animals can infect animals in other cages connected only through an air duct.
9) There is no strong evidence against airborne transmission, and contact tracing shows secondary transmission in crowded, poorly ventilated indoor spaces.
10) There is only limited evidence that the coronavirus spreads through other ways, such as clothes, furniture and other objects, or through large droplets.

"We thought we'd summarize [the evidence] to clarify the arguments for and against. We looked hard for evidence against but found none," Greenhalgh said.

The evidence on airborne transmission was there very early on but the CDC, World Health Organization and others, repeated the message that the primary concern was droplets and surfaces and objects.

Response to a Review

The top 10 list is also part rebuttal of a WHO review published last month that points to inconclusive evidence for airborne transmission. The researchers involved with that review say that the lack of viral samples of coronavirus “prevents firm conclusions to be drawn about airborne transmission."

However, Greenhalgh and colleagues note that "this conclusion, and the wide circulation of the review's findings, is concerning because of the public health implications."

The current authors also argue that enough evidence already exists on airborne transmission. "Policy should change. We don't need more research on this topic; we need different policy," Greenhalgh said. "We need ventilation front and center, air filtration when necessary, and better-fitting masks worn whenever indoors."

Allen agreed that guidance hasn't always kept pace with the science. "With all of the new evidence accumulated on airborne transmission since last winter, there is still widespread confusion in the public about modes of transmission," he said. Allen also serves as commissioner of The Lancet COVID-19 Commission and is chair of the commission's Task Force on Safe Work, Safe Schools, and Safe Travel.

"It was only just last week that CDC pulled back on guidance on 'deep cleaning' and in its place correctly said that the risk [of being infected with coronavirus] from touching surfaces is low," he added. "The science has been clear on this for over a year, but official guidance was only recently updated."

As a result, many companies and organizations continued to focus on "hygiene theater," Allen said, "wasting resources on overcleaning surfaces. Unbelievably, many schools still close for an entire day each week for deep cleaning and some still quarantine library books. The message that shared air is the problem, not shared surfaces, is a message that still needs to be reinforced."
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Re: Aerosolized Transmission

Post by trader32176 »

Faster air exchange in buildings not always beneficial for coronavirus levels

Modeling study suggests vigorous ventilation can cause spike in viral concentrations

4/22/21 ... 042121.php

Vigorous and rapid air exchanges might not always be a good thing when it comes to addressing levels of coronavirus particles in a multiroom building, according to a new modeling study.

The study suggests that, in a multiroom building, rapid air exchanges can spread the virus rapidly from the source room into other rooms at high concentrations. Particle levels spike in adjacent rooms within 30 minutes and can remain elevated for up to approximately 90 minutes.

The findings, published online in final form April 15 in the journal Building and Environment, come from a team of researchers at the U.S. Department of Energy's Pacific Northwest National Laboratory. The team includes building and HVAC experts as well as experts in aerosol particles and viral materials.

"Most studies have looked at particle levels in just one room, and for a one-room building, increased ventilation is always useful to reducing their concentration," said Leonard Pease, lead author of the study. "But for a building with more than one room, air exchanges can pose a risk in the adjacent rooms by elevating virus concentrations more quickly than would otherwise occur.

"To understand what's happening, consider how secondhand smoke is distributed throughout a building. Near the source, air exchange reduces the smoke near the person but can distribute the smoke at lower levels into nearby rooms," Pease added. "The risk is not zero, for any respiratory disease."

The team modeled the spread of particles similar to SARS-CoV-2, the virus that causes COVID-19, via air-handling systems. Scientists modeled what happens after a person has a five-minute coughing bout in one room of a three-room small office building, running simulations with particles of five microns.

Researchers looked at the effects of three factors: different levels of filtration, different rates of outdoor air incorporation into the building air supply, and different rates of ventilation or air changes per hour. For downstream rooms, they found an expected clear benefit from increasing outdoor air and improving filtering, but the effect of increased ventilation rate was less obvious.

More clean outdoor air reduces transmission

Scientists studied the effects of adding varying amounts of outdoor air to the building air supply, from no outside air to 33 percent of the building's air supply per hour. As expected, the incorporation of more clean outdoor air reduced transmission risk in the connected rooms. Replacement of one-third of a building's air per hour with clean outdoor air in downstream rooms reduced infection risk by about 20 percent compared to the lower levels of outdoor air commonly included in buildings. The team noted that the model assumed that the outdoor air was clean and virus free.

"More outside air is clearly a good thing for transmission risk, as long as the air is free of virus," said Pease.

Strong filtration reduces transmission

The second factor studied--strong filtration--also was very effective at reducing transmission of the coronavirus.

The team studied the effects of three levels of filtration: MERV-8, MERV-11, and MERV-13, where MERV stands for minimum efficiency reporting value, a common measure of filtration. A higher number translates to a stronger filter.

Filtration decreased the odds of infection in the connected rooms markedly. A MERV-8 filter decreased the peak level of viral particles in connected rooms to just 20 percent what it was without filtration. A MERV-13 filter knocked down the peak concentration of viral particles in a connected room by 93 percent, to less than one-tenth of what it was with a MERV-8 filter. The researchers note that the stronger filters have become more common since the pandemic began.

Increasing ventilation--a more complex picture

The most surprising finding of the study involved ventilation--the effect of what researchers call air changes per hour. What's good for the source room--cutting transmission risk within the room by 75 percent--is not so good for connected rooms. The team found that a rapid rate of air exchange, 12 air changes per hour, can cause a spike in viral particle levels within minutes in connected rooms. This increases the risk of infection in those rooms for a few minutes to more than 10 times what it was at lower air-exchange rates. The higher transmission risk in connected rooms remains for about 20 minutes.

"For the source room, clearly more ventilation is a good thing. But that air goes somewhere," said Pease. "Maybe more ventilation is not always the solution."

Interpreting the data

"There are many factors to consider, and the risk calculation is different for each case," said Pease. "How many people are in the building and where are they located? How large is the building? How many rooms? There is not a great deal of data at this point on how viral particles move about in multiroom buildings.

"These numbers are very specific to this model--this particular type of model, the amount of viral particles being shed by a person. Every building is different, and more research needs to be done," Pease added.

Co-author Timothy Salsbury, a buildings control expert, notes that many of the trade-offs can be quantified and weighted depending on circumstances.

"Stronger filtration translates to higher energy costs, as does the introduction of more outside air than would usually be used in normal operations. Under many circumstances, the energy penalty for the increased fan power required for strong filtration is less than the energy penalty for heating or cooling additional outside air," said Salsbury.

"There are many factors to balance--filtration level, outdoor air levels, air exchange--to minimize transmission risk. Building managers certainly have their work cut out for them," he added.

Additional experimental studies underway

The team is already conducting a series of experimental studies along the same lines as the modeling study. Like the newly published study, the additional analyses look at the effects of filtration, outdoor air incorporation and air changes.

These ongoing studies involve real particles made of mucus (not incorporating the actual SARS-CoV-2 virus) and consider differences among particles expelled from various parts of the respiratory tract, such as the oral cavity, the larynx, and the lungs. Investigators deploy an aerosolizing machine that disperses the viral-like particles much as they'd be dispersed by a cough, as well as fluorescent tracking technology to monitor where they go. Other factors include varying particle sizes, how long viral particles are likely to be infectious, and what happens when they drop and decay.


DOE/Pacific Northwest National Laboratory
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Re: Aerosolized Transmission

Post by trader32176 »

Covid-19: What do we know about airborne transmission of SARS-CoV-2?


How covid-19 spreads is one of the most debated questions of the pandemic. Chris Baraniuk explains what the evidence tells us about airborne transmission of the virus

What does airborne transmission mean?

Scientists distinguish between respiratory infectious diseases classed as “airborne”—which spread by aerosols suspended in the air—and infections that spread through other routes, including larger “droplets.”

Aerosols are tiny liquid particles from the respiratory tract that are generated when someone exhales, talks, or coughs, for example. They float in the air and can contain live viruses, such as measles and chickenpox. Both are examples of highly infectious diseases classed as airborne because they are known to spread by aerosols.

On the other hand, illnesses such as influenza are thought to spread primarily through larger respiratory droplets.1 These do not float as easily and are more likely to fall to the ground within 1-2 m of the source.

An airborne disease might be more transmissible overall. For example, aerosols produced by infectious person A could build up in a small, poorly ventilated room over time. Person A might depart the room but leave their aerosols behind. If person B were then to arrive in the room and spend time there, they could potentially become infected through breathing in the contaminated air.

But these two modes of transmission—airborne or aerosol based versus droplet—are not necessarily mutually exclusive and the definitions of “droplet” and “aerosol” are a problem. “They should change the terminology,” says Julian Tang, consultant virologist at the Leicester Royal Infirmary.2 “Droplets hit the ground, they’re not inhaled. Everything else is an aerosol when inhaled, whatever size it is.”

Advice from the World Health Organization states that aerosols are liquid particles of five microns or less in diameter. In reality, larger particles of moisture can also become suspended for a time in the air, depending on conditions such as temperature and humidity, says Tang.3 This means it can be difficult to establish that a virus really has zero opportunity for airborne transmission.4

Is covid-19 airborne?

Some scientists have doubted the aerosol route because covid-19 does not appear as transmissible as, say, measles.5 But others point to cases of covid-19 transmission where airborne spread appears to be the only explanation behind multiple onward infections.

Sneezing and coughing generally produce larger particles of fluid. But evidence shows large quantities of SARS-CoV-2 are also expelled in small aerosols emitted when someone is speaking at a normal volume,6 or merely breathing. One study published in August 2020 found that a single person in the early stages of covid-19 could emit millions of SARS-CoV-2 particles per hour through breathing alone.7

Scientists still aren’t sure how long viable, infectious virus particles can linger in the air. Tang says this is difficult to study because the devices used to sample air destroy viruses, including SARS-CoV-2. Analysis might detect the virus’s RNA but generally find no whole, infectious virus particles. This doesn’t mean viable particles were not present—it might simply be that the sampling technique was unable to retrieve them intact.

Despite these unknowns, several case studies suggest airborne transmission has spread SARS-CoV-2 to distances beyond two metres from the infectious person. In a restaurant in Guangzhou, China, 10 people dined on 24 January 2020, shortly before testing positive for covid-19. Three families were seated around three separate tables, but near to each other. One of the families had recently travelled from Wuhan. There was no interaction between the families sitting at their separate tables, nor obvious routes for transmission by touching contaminated surfaces (fomites). A study of the restaurant’s ventilation systems, security camera footage, and the case histories of those present concluded that infectious particles carried in the air were likely responsible for the spread of the virus.8

Another study, examining an outbreak at an Australian church in July 2020, revealed that a chorister tested positive for covid-19 after developing symptoms.9 Researchers identified 12 secondary cases among churchgoers who were linked to the chorister through genomic sequencing of their SARS-CoV-2 infection. Some of these secondary cases had been sitting 15 m away from the chorister, who was using a microphone and not directly facing those who became infected. The building was minimally ventilated at the time and none of the infected people had worn masks. “We believe that transmission during this outbreak is best explained by airborne spread,” the study authors wrote.

A team of researchers recently argued in the Lancet10 that aerosols were likely to be the dominant route for transmission for SARS-CoV-2. They based this on 10 strands of evidence, including the fact that transmission is much higher indoors than outdoors; and that asymptomatic or pre-symptomatic transmission is thought to have caused a significant number of infections worldwide. When someone is not coughing, they may produce fewer droplets but still emit many aerosols.

What does WHO say about airborne transmission of covid-19?

WHO’s roadmap to improve and ensure good indoor ventilation in the context of covid-19, published 1 March 2021,11 states, “The virus can spread from an infected person’s mouth or nose in small liquid particles when the person coughs, sneezes, sings, breathes heavily, or talks. These liquid particles are different sizes, ranging from larger ‘respiratory droplets’ to smaller ‘aerosols.’

“Aerosol transmission can occur in specific situations in which procedures that generate aerosols are performed.”

WHO was, however, initially adamant that airborne transmission of SARS-CoV-2 was not possible. The agency tweeted on 28 March 2020, “FACT: #COVID19 is NOT airborne.” (The tweet has not been deleted. WHO told The BMJ that their policy is not to delete any communications.) This sparked much debate—in July 2020, 239 scientists signed an open letter “appealing to the medical community and relevant national and international bodies to recognise the potential for airborne spread of covid-19.”12

Since March 2020, WHO has gradually changed its stance. At the time of writing, its official advice reads, “Airborne transmission of SARS-CoV-2 can occur during medical procedures that generate aerosols.”13

Nick Wilson, an anaesthetist at the Royal Infirmary in Edinburgh, questions the emphasis on medical procedures. “Procedures don’t generate many aerosols, people do, the physiology does,” he says.14 He also points to a 2014 WHO report which noted that, for any novel acute respiratory infections that have a high public health risk, “airborne and contact precautions, as well as eye protection, should be added to the routine standard precautions whenever possible, to reduce the risk of transmission.” Precautions include ventilation and spacing of patients.15

According to WHO, in reply to BMJ questions, “Outside of medical facilities, aerosol and airborne transmission can occur in specific circumstances and settings, particularly indoor, crowded, and inadequately ventilated spaces such as restaurants, fitness classes, nightclubs, offices, and places of worship, where infected people spend long periods of time with others.”

The agency added that the term “airborne” has a specific medical meaning that applies to diseases such as measles, which transmit predominantly through the air and across long distances. “For covid-19,” WHO added, “the virus predominantly spreads through close, or direct, contact, or possibly contaminated surfaces. That is why it is not called an airborne virus.”

In other words, the agency is currently of the opinion that viral transmission by aerosols, while possible for covid-19, is not the main route by which SARS-CoV-2 spreads.

What do national governments say about airborne transmission of covid-19?

At the time of writing, UK advice states that covid-19 spreads “through the air by droplets and smaller aerosols” and notes that infectious particles can “remain suspended in the air for some time indoors, especially if there is no ventilation.”16 The government’s main public safety messaging of “hands, face, space,” to remind people to wash their hands, wear face masks, and keep distant from one another, was recently updated to include “fresh air,” to encourage people meeting to stay outdoors.

In the US, the Centers for Disease Control and Prevention (CDC) updated its advice on 5 October 2020, acknowledging “the existence of some published reports showing limited, uncommon circumstances where people with covid-19 infected others who were more than 6 feet away or shortly after the covid-19-positive person left an area. In these instances, transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise. Such environments and activities may contribute to the build-up of virus carrying particles.”17

Other countries, such as Australia, make no mention of airborne or aerosol based transmission in their official guidance on how covid-19 spreads.

How can we prevent airborne transmission?

Advice from governments includes ventilation—such as opening windows—and avoiding enclosed spaces. Japan puts emphasis on avoiding the “3Cs”: crowded places, close contact, close conversations—this is echoed in WHO communications that emphasise location, proximity, and time. There is some evidence for this from modelling studies. In one, researchers estimated that the risk of infection could be three times higher in a poorly ventilated room as opposed to one that underwent 10 air changes per hour.18

The installation of air filtering units such as those with high efficiency particulate air filters or specialised ventilation systems could also help. This may be one reason why some governments are reluctant to officially declare SARS-CoV-2 “airborne,” says Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds. “If you think something transmits on surfaces, it’s easy to do a precautionary approach and tell everybody to wash their hands. But if we say it’s in the air, that means some quite major capital investments to buildings and technologies,” she says. Installing energy hungry systems has environmental downsides too.

Do masks prevent airborne transmission?

Some have claimed that airborne transmission would mean face masks were ineffective, since aerosols carrying the virus might pass through microscopic holes in the cloth of a mask. But Noakes says the heightened humidity inside a face mask could help to catch these particles, should they be emitted by the wearer.

She adds that cloth masks—unlike filtering masks such as the N95—may offer only limited protection against breathing in aerosols if they are already suspended in the air. Tang notes that tighter fitting masks or wearing two masks might reduce the emission of aerosols from a source and the inhalation by a recipient wearer.

Still, Wilson says looser fitting masks block or deflect most exhaled air, which reduces its velocity.

How does airborne transmission compare outdoors versus indoors?

There is a risk of covid-19 transmission outdoors, but it is low compared with indoor settings.

In the summer of 2020, widely reported gatherings on British beaches were condemned by some who assumed these events would lead to a spike in covid-19 transmission. In February this year, however, Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, who has advised the government during the pandemic, told MPs, “There were no outbreaks linked to public beaches. There’s never been a covid-19 outbreak linked to a beach, ever, anywhere in the world, to the best of my knowledge.” The Republic of Ireland recently released data suggesting that just 0.1% of covid-19 cases have been linked to outdoor activity.19

Babak Javid, associate professor of medicine at the University of California, San Francisco, argues that it’s time to offer a more nuanced message to the public. Various interventions offer protection he says, but it’s also important to recognise that the risks of particular environments may differ. “If you’re wearing masks, you probably can tolerate a shorter distance between people,” he says, “If you’re outdoors you can be closer to people. If you’re indoors, distance by itself won’t be protective, necessarily.”
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