Reducing transmission of SARS-CoV-2
Correctly fitted masks are an important tool to reduce airborne transmission of SARS-CoV-2, particularly in enclosed spaces, such as on this Moscow Metro train in Russia.
PHOTO: SERGEI FADEICHEV/TASS VIA GETTY IMAGES
Respiratory infections occur through the transmission of virus-containing droplets (>5 to 10 µm) and aerosols (≤5 µm) exhaled from infected individuals during breathing, speaking, coughing, and sneezing. Traditional respiratory disease control measures are designed to reduce transmission by droplets produced in the sneezes and coughs of infected individuals. However, a large proportion of the spread of coronavirus disease 2019 (COVID-19) appears to be occurring through airborne transmission of aerosols produced by asymptomatic individuals during breathing and speaking (1—3). Aerosols can accumulate, remain infectious in indoor air for hours, and be easily inhaled deep into the lungs. For society to resume, measures designed to reduce aerosol transmission must be implemented, including universal masking and regular, widespread testing to identify and isolate infected asymptomatic individuals.
Humans produce respiratory droplets ranging from 0.1 to 1000 µm. A competition between droplet size, inertia, gravity, and evaporation determines how far emitted droplets and aerosols will travel in air (4, 5). Larger respiratory droplets will undergo gravitational settling faster than they evaporate, contaminating surfaces and leading to contact transmission. Smaller droplets and aerosols will evaporate faster than they can settle, are buoyant, and thus can be affected by air currents, which can transport them over longer distances. Thus, there are two major respiratory virus transmission pathways: contact (direct or indirect between people and with contaminated surfaces) and airborne inhalation.
In addition to contributing to the extent of dispersal and mode of transmission, respiratory droplet size has been shown to affect the severity of disease. For example, influenza virus is more commonly contained in aerosols with sizes below 1 µm (submicron), which lead to more severe infection (4). In the case of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is possible that submicron virus-containing aerosols are being transferred deep into the alveolar region of the lungs, where immune responses seem to be temporarily bypassed. SARS-CoV-2 has been shown to replicate three times faster than SARS-CoV-1 and thus can rapidly spread to the pharynx, from which it can be shed before the innate immune response becomes activated and produces symptoms (6). By the time symptoms occur, the patient has transmitted the virus without knowing.
Identifying infected individuals to curb SARS-CoV-2 transmission is more challenging compared to SARS and other respiratory viruses because infected individuals can be highly contagious for several days, peaking on or before symptoms occur (2, 7). These “silent shedders” could be critical drivers of the enhanced spread of SARS-CoV-2. In Wuhan, China, it has been estimated that undiagnosed cases of COVID-19 infection, who were presumably asymptomatic, were responsible for up to 79% of viral infections (3). Therefore, regular, widespread testing is essential to identify and isolate infected asymptomatic individuals.
Airborne transmission was determined to play a role during the SARS outbreak in 2003 (1, 4). However, many countries have not yet acknowledged airborne transmission as a possible pathway for SARS-CoV-2 (1). Recent studies have shown that in addition to droplets, SARS-CoV-2 may also be transmitted through aerosols. A study in hospitals in Wuhan, China, found SARS-CoV-2 in aerosols further than 6 feet from patients, with higher concentrations detected in more crowded areas (8). Estimates using an average sputum viral load for SARS-CoV-2 indicate that 1 min of loud speaking could generate >1000 virion-containing aerosols (9). Assuming viral titers for infected super-emitters (with 100-fold higher viral load than average) yields an increase to more than 100,000 virions in emitted droplets per minute of speaking.
The U.S. Centers for Disease Control and Prevention (CDC) recommendations for social distancing of 6 feet and hand washing to reduce the spread of SARS-CoV-2 are based on studies of respiratory droplets carried out in the 1930s. These studies showed that large, ∼100 µm droplets produced in coughs and sneezes quickly underwent gravitational settling (1). However, when these studies were conducted, the technology did not exist for detecting submicron aerosols. As a comparison, calculations predict that in still air, a 100-µm droplet will settle to the ground from 8 feet in 4.6 s, whereas a 1-µm aerosol particle will take 12.4 hours (4). Measurements now show that intense coughs and sneezes that propel larger droplets more than 20 feet can also create thousands of aerosols that can travel even further (1). Increasing evidence for SARS-CoV-2 suggests the 6 feet CDC recommendation is likely not enough under many indoor conditions, where aerosols can remain airborne for hours, accumulate over time, and follow airflows over distances further than 6 feet (5, 10).
Masks reduce airborne transmission
Infectious aerosol particles can be released during breathing and speaking by asymptomatic infected individuals. No masking maximizes exposure, whereas universal masking results in the least exposure.
GRAPHIC: V. ALTOUNIAN/SCIENCE
In outdoor environments, numerous factors will determine the concentrations and distance traveled, and whether respiratory viruses remain infectious in aerosols. Breezes and winds often occur and can transport infectious droplets and aerosols long distances. Asymptomatic individuals who are speaking while exercising can release infectious aerosols that can be picked up by airstreams (10). Viral concentrations will be more rapidly diluted outdoors, but few studies have been carried out on outdoor transmission of SARS-CoV-2. Additionally, SARS-CoV-2 can be inactivated by ultraviolet radiation in sunlight, and it is likely sensitive to ambient temperature and relative humidity, as well as the presence of atmospheric aerosols that occur in highly polluted areas. Viruses can attach to other particles such as dust and pollution, which can modify the aerodynamic characteristics and increase dispersion. Moreover, people living in areas with higher concentrations of air pollution have been shown to have higher severity of COVID-19 (11). Because respiratory viruses can remain airborne for prolonged periods before being inhaled by a potential host, studies are needed to characterize the factors leading to loss of infectivity over time in a variety of outdoor environments over a range of conditions
Given how little is known about the production and airborne behavior of infectious respiratory droplets, it is difficult to define a safe distance for social distancing. Assuming SARS-CoV-2 virions are contained in submicron aerosols, as is the case for influenza virus, a good comparison is exhaled cigarette smoke, which also contains submicron particles and will likely follow comparable flows and dilution patterns. The distance from a smoker at which one smells cigarette smoke indicates the distance in those surroundings at which one could inhale infectious aerosols. In an enclosed room with asymptomatic individuals, infectious aerosol concentrations can increase over time. Overall, the probability of becoming infected indoors will depend on the total amount of SARS-CoV-2 inhaled. Ultimately, the amount of ventilation, number of people, how long one visits an indoor facility, and activities that affect airflow will all modulate viral transmission pathways and exposure (10). For these reasons, it is important to wear properly fitted masks indoors even when 6 feet apart. Airborne transmission could account, in part, for the high secondary transmission rates to medical staff, as well as major outbreaks in nursing facilities. The minimum dose of SARS-CoV-2 that leads to infection is unknown, but airborne transmission through aerosols has been documented for other respiratory viruses, including measles, SARS, and chickenpox (4).
Airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing, and social distancing programs. After evidence revealed that airborne transmission by asymptomatic individuals might be a key driver in the global spread of COVID-19, the CDC recommended the use of cloth face coverings. Masks provide a critical barrier, reducing the number of infectious viruses in exhaled breath, especially of asymptomatic people and those with mild symptoms (12) (see the figure). Surgical mask material reduces the likelihood and severity of COVID-19 by substantially reducing airborne viral concentrations (13). Masks can also protect uninfected individuals from SARS-CoV-2 aerosols and droplets (13, 14). Thus, it is particularly important to wear masks in locations with conditions that can accumulate high concentrations of viruses, such as health care settings, airplanes, restaurants, and other crowded places with reduced ventilation. The aerosol filtering efficiency of different materials, thicknesses, and layers used in properly fitted homemade masks was recently found to be similar to that of the medical masks that were tested (14). Thus, the option of universal masking is no longer held back by shortages.
From epidemiological data, places that have been most effective in reducing the spread of COVID-19 have implemented universal masking, including Taiwan, Japan, Hong Kong, Singapore, and South Korea. In the battle against COVID-19, Taiwan (population 24 million, first COVID-19 case 21 January 2020) did not implement a lockdown during the pandemic, yet maintained a low incidence of 441 cases and 7 deaths (as of 21 May 2020). By contrast, the state of New York (population ∼20 million, first COVID case 1 March 2020), had a higher number of cases (353,000) and deaths (24,000). By quickly activating its epidemic response plan that was established after the SARS outbreak, the Taiwanese government enacted a set of proactive measures that successfully prevented the spread of SARS-CoV-2, including setting up a central epidemic command center in January, using technologies to detect and track infected patients and their close contacts, and perhaps most importantly, requesting people to wear masks in public places. The government also ensured the availability of medical masks by banning mask manufacturers from exporting them, implementing a system to ensure that every citizen could acquire masks at reasonable prices, and increasing the production of masks. In other countries, there have been widespread shortages of masks, resulting in most residents not having access to any form of medical mask (15). This striking difference in the availability and widespread adoption of wearing masks likely influenced the low number of COVID-19 cases.
Aerosol transmission of viruses must be acknowledged as a key factor leading to the spread of infectious respiratory diseases. Evidence suggests that SARS-CoV-2 is silently spreading in aerosols exhaled by highly contagious infected individuals with no symptoms. Owing to their smaller size, aerosols may lead to higher severity of COVID-19 because virus-containing aerosols penetrate more deeply into the lungs (10). It is essential that control measures be introduced to reduce aerosol transmission. A multidisciplinary approach is needed to address a wide range of factors that lead to the production and airborne transmission of respiratory viruses, including the minimum virus titer required to cause COVID-19; viral load emitted as a function of droplet size before, during, and after infection; viability of the virus indoors and outdoors; mechanisms of transmission; airborne concentrations; and spatial patterns. More studies of the filtering efficiency of different types of masks are also needed. COVID-19 has inspired research that is already leading to a better understanding of the importance of airborne transmission of respiratory disease.
Acknowledgments
The authors thank S. Strathdee, D. Petras, and L. Marr for helpful discussions. K.A.P. is supported by the NSF Center for Aerosol Impacts on Chemistry of the Environment (CHE1801971). R.T.S. is supported by the National Institute of Allergy and Infectious Diseases (R01 AI131424). C.C.W. is supported by the Ministry of Science and Technology (MOST 108-2113-M-110-003) and the Higher Education Sprout Project of the Ministry of Education, Taiwan, ROC.
Supplementary Material
References and Notes
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L. Morawska, J. Cao, Environ. Int. 139, 105730 (2020).
2
E. L. Anderson et al., Risk Anal. 40, 902 (2020).
3
S. Asadi et al., Aerosol Sci. Technol. 54, 635 (2020).
4
R. Tellier et al., BMC Infect. Dis. 19, 101 (2019).
5
R. Mittal, R. Ni, J.-H. Seo, J. Fluid Mech. 10.1017/jfm.2020.330 (2020).
6
H. Chu et al., Clin. Infect. Dis. 10.1093/cid/ciaa410 (2020).
7
X. He et al., Nat. Med. 26, 672 (2020).
8
Y. Liu et al., Nature 10.1038/s41586-020-2271-3 (2020).
9
V. Stadnytskyi et al., Proc. Natl. Acad. Sci. U.S.A. 202006874 (2020).
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G. Buonanno, L. Stabile, L. Morawska, Environ. Int. 141, 105794 (2020).
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E. Conticini, B. Frediani, D. Caro, Environ. Pollut. 261, 114465 (2020).
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N. H. L. Leung et al., Nat. Med. 26, 676 (2020).
13
J. F.-W. Chan et al., Clin. Infect. Dis. 10.1093/cid/ciaa644 (2020).
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A. Konda et al., ACS Nano 10.1021/acsnano.0c03252 (2020).
15
C. C. Leung, T. H. Lam, K. K. Cheng, Lancet 395, 945 (2020).
Information & Authors
Information
Published In
Science
Volume 368 • Issue 6498 • 26 June 2020
Pages: 1422 - 1424
PubMed: 32461212
History
27 May 2020
Copyright
Copyright © 2020, American Association for the Advancement of Science.
This is an article distributed under the terms of the Science Journals Default License.
RE: Asymptomatic Spread
In reviewing evidence from this article I was searching for clinical or confirmed asymptomatic spread. This is critical information to guide both policy and individual choices during the current epidemic. I was rather dissapointed to find that of the three citations offered for "However, a large proportion of the spread of coronavirus disease 2019 (COVID-19) appears to be occurring through airborne transmission of aerosols produced by asymptomatic individuals during breathing and speaking." none provided me with concrete or reliable data. The first entirely lacked the word asymptomatic, the second relates anecdotal unconfirmed case studies, and the third is a theoretical rational for aerosol asymtomatic spread with no original data related to Covid-19. I understand the desire to produce information for the research and political populations, but expect stronger citation confirmation and reference from this publication.
RE: Electron beam irradiation in covid 19 virus may be a solution for when it is aerosol based transmission in closed space like in hospital covid wards out patients departments, Emergency rooms,in fomites and also for strilisation of PPEkits
Dear Editor
The novel Corona virus pneumonia triggered by covid 19 is raging the whole world.This covid 19 virus spread from a sea market in Wuhan , China or from a virological lab BSL 4 lab in December 2019 in Wuhan China is controversial issues. Till 10.8.2020 the covid 19 SARS covid 2 virus killed 740435(5%) cases and infected 20,321,325 cases, with active cases 6,337558 when recovered 13,243,339(95%) affected 213 countries having highest in USA, followed by Brazil and India is in 3rd position with total cases 22,94,438,daily infection 27,285as new positive cases and total death 45,597 (2%), active cases 6,44,722,total cases per million population in India 1,661, total death per million is 33. So far in world 7,40,435 has been killed and 20 million 32 lakh people infected, billions of people were / are isolated at home ( for lock down, as with mild symptoms or asymptotic positive cases) or admitted in hospital to avoid cross infection by droplets or by aerosal in closed environment and in hospital SARI or covid hospital wards..No effective antiviral drugs are yet available and various antiviral medications are on trial. Multiple vaccines are also on phase 2 or phase 3 trial in human subjects including a russian vaçcine. The only methods are to avoid contact infection for public at large using masks ( preferably N95 masks), face shield, eye gaugles , frequently hand washing with soaps or 70% alcohol that disrupt viral lipid envelopes.Many kinds of disinfectants like sodium hypochlorite, hydrogen peroxide spraying are used as environmental sterilisation and 70% alcohol are used for hand sanitizer.what about the virus killing when it is in micro droplets or nuclue droplets if in aerosol generated in closed spaces like small rooms,in laboratory,in office rooms,in hospital wards,in operation theatre,in out patients departments or in various industries, schools, colleges, gyms, restaurant malls where aerosols are generated and virus can be air borne one ,in short distance even ? Only use of Masks,face shield, gaugles and physical distensing will be only safety measures? Then why the virus spreading so rapidly in 213 countries and still infecting thousands every day in countries
It is well known that electron beam irradiation with a specific voltage and energy or non thermal plasma energy (NTP) can inactivate mortigenious micro organisms which may attach to any fomite food or present in air. Electron beam energy or NTP can kill or disinfect many bacteria like gram positive and gram negetive bacteria including staphylococcus, streptococcus, E.coli, salmonella . Electron beam or NTP energy exposure within packed bed dielectric barirr are found exponentially increased inactivate of aerosolised MS2 phage with increasing voltage of 30 kv and at an air flow rate of 170 standard liter per minute.ozone can be generated by this process can effectively reduce the viral load in the aerosols (1) found in acute respiratory disease of previous SARS and MERS. Moreover electron beam irradiation have huge potential on food safety and vaçcine decontamination (2) PPE sterilisation etc. However though many physicists proposed and carried out investigations about electron beam irradiation of virus that can not only destroy viral envelopes protein but also viral nucleocapsid and RNA or DNA depending on irradiation KV and energy,owing to rapid outbreak disaster. It must be realised how much electron beam or NTP irradiation will effect on covid 19 Corona virus as in aerosol or in fomites or in food safety or in wards or in closed room
How does the irradiated electrons interacts with Corona virus Covid 19 is not known well yet. The novel Corona virus 19 is first sorrounded by spike glycoprotein,then under spike protein there are more than one layer of envelope protein and small fraction of hemagglutinin to help the virus to attach to the cells . inside the novel Corona virus the nucleocapsid closely attached the RNA. Both of them wandering inside the virus together with a gap space and RNA has a random movement.The viral particle is 120nm . Molecular formula for spike protein , envelope protein,and nucleocapsid are as follows C4.99458H9.6732O2.4870N1.1987S.0424: C5.2297H10.20301.2523N2.3514S0.0360 and C4.6108H9.2925O2.4505N1.3042S0.0165 respectively (3) which means that these proteins bonds can be disruptive by energy. When an incident electron or non thermal plasma irradiate inside the covid 19 virus a series of collision process must occur between energetic electrons and the viral structure molecule as described above. Based on the energy loss situation of collision process are devided into classic scattering process without energy loss and in elastic scattering process with energy loss based on scattering angles during collision between electrons and viral structure atoms based on Ratherford mode (3) and it is the inelastic scattering process that not only change the angle of scattering but also transfer energy to interact with viral protien structure.The energy of electron transfer from mostly during the inelastic scattering.When an electron hits the virus a series of Monte Carlo reaction occurs (3) which can judge and will occur with each collision and during inelastic scattering between electrons and covid 19 virus atoms,part of electron energy will transform into into atoms and results atom ionisation and inner secondary electron
Is generated that break the viral molecular chain and can destroy the covid 19 virus.Each inelastic scattering will cause ionisation and will excite also a pair of free electron to produce a hole ( like free radical produces a hole in bacterial membrane) in the spike protein, in the envelopes and nucleocapsid of covid 19 virus. The maximum break down occur will be then in spike protien.when the atom ionisation energy is 1Kv the incident electron will not be able to reach all virus area but only upper area are will be ionized and envelope protein of covid 19 will be disrupted. When the incident energy is 5Kv incident electron can reach all areas of the virus and can destroy the whole virus including its RNA
So if a device that release electron beam or non thermal plasma can attract the sorrounded virus on its surface and will destroy the covid 19 virus to keep the area virus free
References
1) This A, Kleinheksie,EM Lee,Z Qvao, KR winggton and H.L Clack " Inactivation of air borne viruses using packed bad non thermal plasma reactor " journal of Physics D: Applied physics vol 52 N25;23rd April 2019
2) Luchsinger SE,Krof DH ,Gracia zepeda C.M , Food Sciences vol 61, 1000, 2006 DOI -10.1111/j.1365-2621.1996.tb10920.x.
3) Guobao Feng, LuLiu , Wanzhio CU,Fang Wang " Electron beam irradiation on corana viruses a Monte Carlo simulation" Clin.Phys.B vol 29 N4 048703;2020
This article as e letter at journal Science are copyrighted material to authors as per copy right acts and rules of IPR and RDF copy right rules to authors only
Acknowledgement -: To our diseased parents Late Bholanath Bhattacharya and Late Mrs Bani Bhattacharya of 7/51 Purbapalli ,sodepur ,24 parganas ,north, kolkata 110, west Bengal ,India and to my late all maternal uncles , aunts and late paternal side uncles and grand mother late Saila Bala chakraborty
Prediction from clinical experiments is sometimes important rather than the evidence
Drs, Prather, Wang, And Schooley showed us timely perspectives in last issue. (26 June 2020 1422-1424)1. They mentioned the importance about the mask reduces airborne transmission. In that literature they also suggested that the distance from a smoker at which one smells cigarette smoke indicates the distance in those surroundings at which one could inhale infectious aerosols. Virus can attach to other particles such as dust and pollution, which can modify the aerodynamic characteristics and dispersion. The terms of this explanation were very helpful to every citizen in the world.
Their perspectives are based in the Evidence based medicine. Of course, evidence is the most important thing in the medicine as one of a Science.
COVID-19 may bring us many scientific evidences.
However, only a mask and hand wash can be suggested as current evidence so far.
In this particular pandemic situation, to try a predictable positive prediction or experiment-based medicine is important rather than the evidence because we have no time to wait the evidence.
In surgery, first we wear the cap, shoe cover and mask, then wash our hand, wear a surgical gown and groves to reduce transmission of the bacteria or virus. Furthermore, in an aseptic room, we remove those particles which included bacteria and virus through the filters by using aerodynamic circulation cycle.
Therefore, we strongly suggest to remove the mask and dust off of hair and clothes, removing and disinfecting the shoes2 before entering the house then wash hands and gargle to reduce predictable transmission.
References
1. Prather KA, Wang CC, Schooley RT. Reducing transmission of SARS-CoV-2. Science. 2020;368(6498):1422-1424. doi:10.1126/science.abc6197
2. Koichi Tsunod, Mihiro Takazawa. A Simple Custom Could Prevent Spread of SARS-CoV-2, (comment on June 3, 2020) Nardell EA, Nathavitharana RR. Airborne Spread of SARS-CoV-2 and a Potential Role for Air Disinfection. JAMA. Published online June 01, 2020. doi:10.1001/jama.2020.7603 doi:10.1001/jama.2020.7603
Airborne Spread of SARS-CoV-2 and a Potential Role for Air Disinfection
RE: Dr. D.V. Gokhale
This is very interesting and realistic perspective on reducing the transmission of SARS-CoV-2 infection suggesting emphatically the use mask to combat the asymptomatic spread via aerosoles and droplets that are less than 1micron. The authors pointed out the limitations of social distancing of 6 feet recommended by CDC. These recommendations were based on studies on the infected droplets of 100 microns thrown out by coughs and sneezes of the infected individual. These droplets being heavy, settle down due to gravitation force. Probably, nobody thought of droplets or particles of less than 1 micron size produced in sneezes and coughs which remain in air for hours together and carried away to longer distances because winds and breezes. These droplets may be more responsible for spreading of COVID-19 disease. However, not much information is available on the role of airborne infectious droplets in causing COVID-19 and hence the conclusions of this perspective seems to be illogical. It is necessary to undertake such studies to authenticate the airborne transmission of SARS-CoV-2 virus which will help CDC to take decisions and and issue recommendations to reduce the speard of COVID-19 disease.
RE: Wearing a mask in the era of COVID-19 makes all the difference
Prather, K. A. et al. have raised a good point - places that have been most effective in reducing the spread of COVID-19 have implemented universal masking (1). While most countries of Eastern Asia have been successful in controlling the COVID-19 pandemic, many European/American countries continue to suffer from rapid spread of the virus. Virus transmission in three East Asian countries, including Japan, South Korea, and China, seem to be under control, as their total infection curves have been almost horizontal from February 20 to May 15, 2020, whereas the curves of many European/American countries have risen very fast, especially that of the USA, which is almost vertical. What accounts for this difference?
Close interactions among people in large clusters, such as workplaces, may contribute to the number of infections. It follows that countries with greater populations would spread the coronavirus faster. Yet, compared with one country (USA) from North America and five countries from Europe, the three East Asian countries have higher population density. This seems to indicate that high population density did not accelerate virus transmission in these countries. Establishment of travel restrictions worked successfully in controlling the pandemic early in the year in China, but it was not helpful in the Western countries, possibly because it is too late to take these measures. Iinterestingly, no strict travel restrictions have been implemented in Japan and South Korea, even though they were successful in controlling the pandemic.
To explain, we look to the acceptance of face covering as a key difference between Eastern Asian countries and European/American countries. This alone was and is a notable preventive measure adopted by China early on in the pandemic. However, across European/American countries, we saw and see a hesitation to accept face covering. Data show that most countries recommended, or required, the public to wear face covering after April 2, but belatedly, because this step was implemented after their total confirmed infection number had risen more than 150,000. In contrast, the Japanese, South Koreans, and Chinese started to wear masks in January and on into March when the total number of cases was only in the hundreds. Due to the fact that SARS-CoV-2 is transmitted through air droplets and features asymptomatic carriers, universal mask wearing would be one of the most effective measures in controlling the transmission of the virus from its ability to filter out and keep in air droplets (2).
Culturally, wearing masks in East Asian countries is seen as a mutual obligation and a collective responsibility, showing that the mask wearer is conscientious and responsible. In the West, however, mask-wearing is stigmatized and seen as spreading unnecessary panic (3), indicating that sociocultural factors may affect the attitude towards wearing masks. Therefore, across cultural divides and societal differences, good public health practices, such as covering the face, must prevail if we are to control COVID-19 as one world.
REFERENCES AND NOTES
1. K. A. Prather, C. C. Wang, R. T. Schooley, Reducing transmission of SARS-CoV-2. Science (80-. )., eabc6197 (2020).
2. N. H. L. Leung, D. K. W. Chu, E. Y. C. Shiu, K. H. Chan, J. J. McDevitt, B. J. P. Hau, H. L. Yen, Y. Li, D. K. M. Ip, J. S. M. Peiris, W. H. Seto, G. M. Leung, D. K. Milton, B. J. Cowling. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat. Med. 26:676-680 (2020).
3. B. J. Strasser, T. Schlich. A history of the medical mask and the rise of throwaway culture. Lancet; https://doi.org/10.1016/S0140-6736(20)31207-1 (2020).
Reducing transmission of SARS-CoV-2 - the clinical relevance and practical application of scientific research studies during a global Pandemic
To the Editor,
I read with keen interest the perspective piece by Prather, K. A. et al. (1) and titled "Reducing transmission of SARS-CoV-2".
This perspective piece provides a brief and helpful summary of some of the studies related to airborne transmission of respiratory disease, in the context of the current Pandemic crisis and the issue of asymptomatic transmission.
Masks and widespread testing are integral to combating asymptomatic spread in aerosols and droplets, and in particular the identification and isolation of symptomatic and any asymptomatic individuals as rapidly as possible, is also essential.
The role of rapid and effective contact tracing processes, lockdown and quarantine measures coupled with the appropriate border controls are also absolutely critical in managing this current global crisis.
It is also a necessity to ensure availability and communication of the scientific studies underpinning the public health and physical distancing recommendations being put forward during the current COVID-19 pandemic.
This helps provide assurance that a sound evidence base underlies the decisions and recommendations being made.
This also provides a valuable opportunity for children and young people – the next generation of scientists, to see the immediate clinical relevance and the important practical application of scientific research studies during a global Pandemic.
Overall this brief review provides a helpful summary of direct relevance to the current Pandemic.
Respectfully yours,
Dr Dianne Sika-Paotonu CQS MRSNZ
Associate Dean (Pacific)
Senior Lecturer, Pathology & Molecular Medicine
Head, University of Otago Wellington Pacific Office
Wellington School of Medicine and Health Sciences, University of Otago, New Zealand
Honorary Research Associate, Telethon Kids Institute, Australia
Honorary Research Associate, Victoria University of Wellington, New Zealand
Associate Investigator Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, New Zealand
References:
1. Prather, K. A., Wang, C. C., & Schooley, R. T. (2020). Reducing transmission of SARS-CoV-2. Science.
RE: Nebulizer therapy with isotonic saline to decrease aerosol transmission of SARS-CoV-2
The ongoing response to COVID-19 pandemic remains focused on social distancing measures to slow the spread of SARS-CoV-2. Airborne transmission of virus-containing aerosols produced by asymptomatic individuals appears to be the main mechanism responsible for the spread of COVID-19. In their Perspective article 'Reducing transmission of SARS-CoV-2' (27 May 2020: eabc6197), K. A. Prather et al. discuss the need for control measures that will reduce aerosol transmission of SARS-CoV-2, specifically, universal masking and widespread testing to identify and isolate infected asymptomatic individuals (1).
In this context, it is somewhat surprising that the study by Edwards et al. (2004) has not received much attention. Edwards et al. found that superemitters (human subjects that expire excessive bioaerosol particles during quiet breathing) could potentially play the role of superspreaders for respiratory pathogens. More importantly, they have shown that the administration of nebulized isotonic saline in such individuals significantly diminished the number of exhaled bioaerosol particles for up to 6 hours (2).
Nebulization therapy in general has a good safety profile, is suitable for most patients (including children, elderly, patients on mechanical ventilation), and is widely used in many respiratory diseases (3). The effectivity of such an intervention in the context of SARS-CoV-2 transmission can be rapidly determined in the current outbreak scenario. Once assessed, nebulizer therapy with isotonic saline can be added to the treatment regime of hospitalized COVID-19 patients, both mechanically ventilated as well as non-ventilated patients. The costs of such addition are negligible, and the reduced viral loads would provide tremendous benefits as the risk of acquiring infection in hospital settings would decrease. Furthermore, portable and at-home use nebulizers are readily available in the market, and nebulizer therapy can be broadly recommended regardless of testing status.
REFERENCES AND NOTES
1. K. A. Prather, C. C. Wang, R. T. Schooley, Reducing transmission of SARS-CoV-2. Science (80-. )., eabc6197 (2020).
2. D. A. Edwards, J. C. Man, P. Brand, J. P. Katstra, K. Sommerer, H. A. Stone, E. Warded, G. Scheuch, Inhaling to mitigate exhaled bioaerosols. Proc. Natl. Acad. Sci. U. S. A. (2004), doi:10.1073/pnas.0408159101.
3. M. Ibrahim, R. Verma, L. Garcia-Contreras, Inhalation drug delivery devices: Technology update. Med. Devices Evid. Res. (2015), , doi:10.2147/MDER.S48888.
RE: An idea
What if you get a covid positive person to wear a mask in a sterile space the has vertical petri dishes set up at various distances. Have the person cough. Next room/space, same, but no cough. Next room/space, different type of mask, etc.
Illogical conclusion
The authors suggest that COVID-19 aerosol spread approximates the diffusion of cigarette smoke, and that such aerosols produced by asymptomatic infected individuals can efficiently infect others. If so, then it does not follow logically that cloth masks, even with social distancing, could possibly support safe return to crowded urban social life. The authors should rethink their premise, as they show no evidence of scientific tentativeness and zeal to falsify their hypothesis that are the hallmarks of evidence-based medicine and public health. It is tempting to abandon high standards of evidence during a pandemic. However, a well designed, safety monitored, adaptive randomized controlled trial is necessary and ethical to test the unproven hypothesis that mandatory masking is effective and safe (as worn by the general public, properly or not). Masks may potentially be contaminated, concentrating virus on the face. Are they assumed to be absolutely safe?
RE: Confusion over social distancing rules
Though the perspective has highlighted the importance of social distancing, it has a factual error. Prather et al wrote that "the World Health Organization (WHO) recommendations for social distancing of 6 ft and hand washing to reduce the spread of SARS-CoV-2 are based on studies of respiratory droplets carried out in the 1930s". However, the WHO recommends just 3 ft of social distancing. I think, the reason for the confusion is the US CDC, which recommends 6 ft of social distancing. The Covid-19 became a classic case of extreme scientific confusion especially in terms of social distancing. There is a discrepancy in social distancing rules across different countries. Some countries follow the WHO recommendations, other countries follow the US CDC , and a few others opted for the average of the two recommendations. For instance, India recommends 1 meter (3ft) . In contrast, Australia suggests keeping 1.5 meters away from others wherever possible. Japan adopted 1.8 (6ft) meters rule. These variations create confusion among people in a given globalized world and raise a legitimate question on 'discrepancies in expert advice' for the same science.
RE: Can we reduce transmission of SARS-CoV-2 by Nasal Wash?
Perspective by Prather et al brought the aerosol transmission of COVID-19 by the asymptomatic individuals in the frontline and posed further challenge. Particles of aerosol can be scattered over a wider area and can cause more severe diseases as they might evade the 'natural ambush' of long slender respiratory tract to instantly reach the lung alveoli.
Mask, distancing and hand wash might not be able to control the aerosol adequately. Virucidal effect of drugs might not be effective due to their higher load at symptomatic stage [Ref 6] unlike SARS and MERS. Vaccine is not expected to be the magic bullet. So what can be done in this pandemonium?
If we ponder from a different point of view, we might get a solution.
At the outset, COVID-19 virions replicate in nasal epithelial cells with hurdles as the nasal mucus gel is the barrier and keeps the virions away from nasal epithelial cells. Nevertheless, eventually, they increase the virion load which is the factor for transmissibility, pathogenicity, fatality [1] and drug resistance [Ref. 6]. So, we have to reduce the virion load.
We, pediatric surgeons, do prophylactic bowel wash with saline water to clear the load of microorganisms from gut, prior to some surgeries to protect small infants from wound infection, sepsis, septic shock or death.
COVID-19 virions are 'surface virions' as they replicate and shed on nasopharyngeal epithelial surface and they are within easy reach; unlike HIV, Dengue etc. So it appears possible to reduce the COVID-19 virion load by repurposing the concept of 'wash' done in pediatric surgery. It seems effectual to wash out virion load in nasal cavity with saline water spray and to wash out pharyngeal virions by means of gargle with antimicrobial solutions to reduce the production of droplets and aerosols contaminated with virions.
References:
1. Liu Y, Yan LM, Wan L, Xiang TX, Le A, Liu JM et al. Viral dynamics in mild and severe cases of COVID-19. Lancet Infect Dis 2020. https://doi.org/10.1016/ S1473-3099(20)30232-2
RE: Ignore masks when we exit from lockdown reopen is illogical
Most people practise the trio of social distancing, hand washing and cough etiquette religiously but many still do not believe that wearing mask is helpful. Comparing these interventions,
● All aim at preventing infections arising from droplets.
● Mask is a form of source control. Social distancing and hand washing are mitigative. In public health, source control takes precedence.
● Though clinical trial evidence on all of them is either poor or non-existent, all four are based on sound scientific and mechanistic principles
● Masks act on a continuous basis. No one can wash their hands every 10 minutes. And to reopen social distancing has to relax.
National authorities in 90 countries and august bodies such as the Royal Society in the UK have recommended mass masking in the community when we exit from lockdown. Sceptics on masks think that they are all wrong. It is possible - there are many examples in the history of science and public health where experts and authorities made erroneous judgements. If they are indeed wrong on masks, we would have wasted our time wearing them but there are little serious harms. However, if they are correct and we ignore the advice, the consequences are far more serious. Asymptomatic transmissions is an important driving force behind this pandemic. Also, <10% of cases may be responsible for 80% of secondary cases. Masking is an important tool that would help to limit the number of cases arising from these two features.
Ignoring masks is illogical as we reopen for business. If you still think it is not worthwhile, try staying in lockdown.