# ent

id: cord-103945-q3ry13vp
type: MONEY
entity:
  between 50 100µm the deposition and evaporation time scales are very similar hence the effect of composition swiftly disappears once the settling time due to gravity becomes much shorter than the droplet evaporation time scale


id: cord-276649-3zl3pm79
type: ORG
entity:
  Institute of Medicine Committee on Personal Protective Equipment for Healthcare Personnel to Prevent Transmission of Pandemic


id: cord-290277-ndfoppoq
type: ORG
entity:
  Interim Infection Prevention and Control Recommendations for Hospitalized Patients with Middle East Respiratory Syndrome Coronavirus


id: cord-253252-s8fm5rfa
type: DISEASE
entity:
  influenza viruses rhinoviruses coronaviruses respiratory syncytial viruses RSVs and parainfluenza viruses Morawska 2006


id: cord-191527-okxzqzl1
type: DNA
entity:
  TX and RX 2 t 0 t t s 3 for k 1 1 K do 4 for i 1 1 length t do 5 Step 1 Trajectory 6 Calculate s k i


# bib

id: cord-016897-t71f10kv
title: Preventing Airborne Disease Transmission: Implications for Patients During Mechanical Ventilation
author: Flores, Marco V.
date: 2013-05-29
txt: ./txt/cord-016897-t71f10kv.txt
cache: ./cache/cord-016897-t71f10kv.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7121330/
doi: 10.1007/978-3-7091-1496-4_34
summary:
  We discuss the risk of transmitting these procedures and the strategies for mechanical ventilation in future airborne epidemics with special consideration given to the issue of protecting health care workers (HCWs). In contrast to the situation regarding severe acute respiratory syndrome (SARS) or tuberculosis prevention in HCWs, little attention has been given to the importance of HCWs personal protective equipment (PPE) (gowns, gloves, masks) for prevention and management of infl uenza. There is also potential for NIV to reduce the need for intubation in patients with infl uenza pneumonia or chronic respiratory disease, facilitate extubation, and widen the provision of ventilator support outside the intensive care unit (ICU). Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebulizer treatment and chest physiotherapy in clinical practice: implications for management of pandemic infl uenza and other airbone infections Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: a systematic review

abstract:
  The organisms causing respiratory infections such as influenza are spread in droplets or aerosols or by direct or indirect contact with contaminated surfaces. Certain medical procedures have been termed aerosol generating because they are associated with high or augmented inspiratory and expiratory flows, which can increase microbial dissemination. Invasive ventilation maneuvers and noninvasive ventilation (NIV) fall into that category. We discuss the risk of transmitting these procedures and the strategies for mechanical ventilation in future airborne epidemics with special consideration given to the issue of protecting health care workers (HCWs).


id: cord-102746-rimpulm0
title: Physics of Virus Transmission by Speaking Droplets
author: Eaton, W. A.
date: 2020-05-16
txt: ./txt/cord-102746-rimpulm0.txt
cache: ./cache/cord-102746-rimpulm0.txt
extension: .txt
mime: text/plain
url: http://medrxiv.org/cgi/content/short/2020.05.12.20099630v1?rss=1
doi: 10.1101/2020.05.12.20099630
summary:
  Calculations with these equations provide a straightforward way to determine the airborne lifetime of emitted droplets after accounting for the decrease in droplet size from water evaporation. At a relative humidity of 50%, droplets with initial radii larger than about 50 microns rapidly fall to the ground while smaller, potentially-virus containing droplets shrink in size and remain airborne for many minutes. Second, for each relative humidity, how much time does it take for water evaporation to reduce a virus-containing droplet to a size that leaves it floating in air for a sufficiently long time to allow direct transmission of the virus to another person? Determining whether or not a virus-containing droplet will remain airborne to cause an infection requires determination of the rate of evaporation of water, which is a more complex problem and is different for different size regimes.

abstract:
  Droplets of oral fluid emitted by speaking are a long-recognized mechanism of respiratory virus transmission. While there have been many simulations of droplet evaporation to determine whether droplets containing virions remain floating in air or rapidly fall to the ground, they typically conceal the fundamental mechanisms because of the use of numerics. To make the physics of emitted oral fluid droplets easily understood, we present simple and transparent algebraic equations that capture the essential physics of the problem. Calculations with these equations provide a straightforward way to determine the airborne lifetime of emitted droplets after accounting for the decrease in droplet size from water evaporation. At a relative humidity of 50%, droplets with initial radii larger than about 50 microns rapidly fall to the ground while smaller, potentially-virus containing droplets shrink in size and remain airborne for many minutes. Rough estimates of airborne virion emission rates while speaking support the proposal that covering the mouth can help end the pandemic more quickly.


id: cord-103945-q3ry13vp
author: de Oliveira, P. M.
date: 2020-07-24
txt: ./txt/cord-103945-q3ry13vp.txt
cache: ./cache/cord-103945-q3ry13vp.txt
extension: .txt
mime: text/plain
url: http://medrxiv.org/cgi/content/short/2020.07.23.20160648v1?rss=1
doi: 10.1101/2020.07.23.20160648
summary:
  By modelling the evaporation and settling of droplets emitted during respiratory releases and using previous measurements of droplet size distributions and SARS-CoV-2 viral load, estimates of the evolution of the liquid mass and the number of viral copies suspended were performed as a function of time from the release. By modelling the evaporation and settling of droplets emitted during respiratory releases and using previous measurements of droplet size distributions and SARS-CoV-2 viral load, estimates of the evolution of the liquid mass and the number of viral copies suspended were performed as a function of time from the release. The Lagrangian framework, given in Sec. 2(a), is considered in one (vertical) dimension and droplet clouds for two exhalation modes, speaking and coughing, are released at the height of the emitter''s mouth (1.5 m) and then let settle by gravity while evaporating in ambient air.

title:
  Evolution of spray and aerosol from respiratory releases: theoretical estimates for insight on viral transmission

abstract:
  By modelling the evaporation and settling of droplets emitted during respiratory releases and using previous measurements of droplet size distributions and SARS-CoV-2 viral load, estimates of the evolution of the liquid mass and the number of viral copies suspended were performed as a function of time from the release. The settling times of a droplet cloud and its suspended viral dose are significantly affected by the droplet composition. The aerosol (defined as droplets smaller than 5 m resulting from 30 seconds of continued speech has o(1h) settling time and a viable viral dose an order-of-magnitude higher than in a short cough. The time-of-flight to reach 2m is only a few seconds resulting in a viral dose above the minimum required for infection, implying that physical distancing in the absence of ventilation is not sufficient to provide safety for long exposure times. The suspended aerosol emitted by continuous speaking for 1 hour in a poorly ventilated room gives 0.1-11% infection risk for initial viral loads of 10^8-10^10 copies/ml, respectively, decreasing to 0.03-3% for 10 air changes per hour by ventilation. The present results provide quantitative estimates useful for the development of physical-distancing and ventilation controls.


id: cord-129086-ra2njvcz
author: Kumar, Sanjay
date: 2020-10-10
txt: ./txt/cord-129086-ra2njvcz.txt
cache: ./cache/cord-129086-ra2njvcz.txt
extension: .txt
mime: text/plain
url: https://arxiv.org/pdf/2010.06385v1.pdf
doi: nan
summary:
  However, in more recent times, the focus has shifted towards the theoretical investigations of fluid flow mechanisms involved in the virus-laden particles prevention by facemasks. 44 While these experimental studies are essential for the broad characterization and design evaluation of respiratory facemasks, further theoretical and numerical methods and algorithm-based investigations provide a better insight into the facemask''s fluid flow dynamics and the droplet leakage through the facemask openings. The computational fluid flow models have shown their potentials in an improved prediction of the spreading of respiratory virus-laden droplets and aerosols, sensitive to the ambient environment, and crucial to the public health responses. The results revealed that the small droplets travel a larger distance and remain suspended in the air for a longer time under the influence of airflow, supporting the mandatory use of facemasks to prevent the virus. In recent years, the respiratory droplets flow behavior through the facemasks has typically well-predicted using the computational fluid dynamics (CFD) techniques.

title:
  The perspective of fluid flow behavior of respiratory droplets and aerosols through the facemasks in context of SARS-CoV-2

abstract:
  In the unfortunate event of current ongoing pandemic COVID-19, where vaccination development is still at the initial stage, several preventive control measures such as social distancing, hand-hygiene, and personal protective equipment have been recommended by health professionals and organizations. Among them, the safe wearing of facemasks has played a vital role in reducing the likelihood and severity of infectious respiratory disease transmission. The reported research in facemasks has covered many of their material types, fabrication techniques, mechanism characterization, and application aspects. However, in more recent times, the focus has shifted towards the theoretical investigations of fluid flow mechanisms involved in the virus-laden particles prevention by facemasks. This exciting research domain aims to address the complex fluid transport that led to designing a facemask with a better performance. This review paper discusses the recent updates on fluid flow dynamics through the facemasks. Key design aspects such as thermal comfort and flow resistance are discussed. Furthermore, the recent progress in the investigations on the efficacy of facemasks for prevention of COVID 19 spread and the impact of wearing facemasks are presented. Finally, the potential research directions for analyzing the fluid flow behavior are highlighted.


id: cord-148354-3nl3js2x
title: On the utility of cloth facemasks for controlling ejecta during respiratory events
author: Kumar, Vivek
date: 2020-05-05
txt: ./txt/cord-148354-3nl3js2x.txt
cache: ./cache/cord-148354-3nl3js2x.txt
extension: .txt
mime: text/plain
url: https://arxiv.org/pdf/2005.03444v1.pdf
doi: nan
summary:
  We simulate the aerodynamic flow through the mask and the spatial spread of droplet ejecta resulting from respiratory events such as coughing or sneezing. We present the viral load in the air and deposited around the person, and show that wearing even a simple cloth mask substantially decreases the extent of spatial spread of virus particles when an infected person coughs or sneezes. 30 Here, we employ Computational Fluid Dynamics (CFD) simulations to address the influence of homemade face masks on the turbulent clouds that result due to sneezing events, and on the lateral extent of spread of ejecta. When an infected person not wearing a mask sneezes or coughs, virus particles in the large droplets rapidly drop to the floor. Our simulation results conclusively demonstrate that wearing even just a simple cotton mask has a dramatic influence on the air flow and spread of ejecta after a respiratory event.

abstract:
  The utility of wearing simple cloth face masks is analyzed using computational fluid dynamics simulations. We simulate the aerodynamic flow through the mask and the spatial spread of droplet ejecta resulting from respiratory events such as coughing or sneezing. Without a mask, a turbulent jet forms, and droplets with a broad size distribution are ejected. Large droplets (greater than about 125 {mu}m in diameter) fall to the ground within about 2 m, while turbulent clouds transport a mist of small aerosolized droplets over significant distances (~ 5 m), consistent with reported experimental findings. A loosely fitted simple cotton cloth mask (with a pore size ~ 4 microns) qualitatively changes the propagation of the high velocity jet, and largely eliminates the turbulent cloud downstream of the mask. About 12% of the airflow leaks around the sides of a mask, considering a uniform gap of only 1 mm all around, between the face and the mask. The spread of ejecta is also changed, with most large droplets trapped at the mask surface. We present the viral load in the air and deposited around the person, and show that wearing even a simple cloth mask substantially decreases the extent of spatial spread of virus particles when an infected person coughs or sneezes.


id: cord-191527-okxzqzl1
author: Gulec, Fatih
date: 2020-07-15
txt: ./txt/cord-191527-okxzqzl1.txt
cache: ./cache/cord-191527-okxzqzl1.txt
extension: .txt
mime: text/plain
url: https://arxiv.org/pdf/2007.07598v1.pdf
doi: nan
summary:
  An end-to-end system model which considers the pathogen-laden cough/sneeze droplets as the input and the infection state of the human as the output is proposed. An end-to-end system model which considers the pathogen-laden cough/sneeze droplets as the input and the infection state of the human as the output is proposed. This model uses the gravity, initial velocity and buoyancy for the propagation of droplets and a receiver model which considers the central part of the human face as the reception interface is proposed. This model uses the gravity, initial velocity and buoyancy for the propagation of droplets and a receiver model which considers the central part of the human face as the reception interface is proposed. Furthermore, the probability of infection for an uninfected human is derived by modeling the number of propagating droplets as a random process. Furthermore, the probability of infection for an uninfected human is derived by modeling the number of propagating droplets as a random process.

title:
  A Molecular Communication Perspective on Airborne Pathogen Transmission and Reception via Droplets Generated by Coughing and Sneezing

abstract:
  Infectious diseases spread via pathogens such as viruses and bacteria. Airborne pathogen transmission via droplets is an important mode for infectious diseases. In this paper, the spreading mechanism of infectious diseases by airborne pathogen transmission between two humans is modeled with a molecular communication perspective. An end-to-end system model which considers the pathogen-laden cough/sneeze droplets as the input and the infection state of the human as the output is proposed. This model uses the gravity, initial velocity and buoyancy for the propagation of droplets and a receiver model which considers the central part of the human face as the reception interface is proposed. Furthermore, the probability of infection for an uninfected human is derived by modeling the number of propagating droplets as a random process. The numerical results reveal that exposure time and sex of the human affect the probability of infection. In addition, the social distance for a horizontal cough should be at least 1.7 m and the safe coughing angle of a coughing human to infect less people should be less than -25$^circ$.


id: cord-208426-wz3jan5d
title: Airborne dispersion of droplets during coughing: a physical model of viral transmission
author: Li, Hongying
date: 2020-08-05
txt: ./txt/cord-208426-wz3jan5d.txt
cache: ./cache/cord-208426-wz3jan5d.txt
extension: .txt
mime: text/plain
url: https://arxiv.org/pdf/2008.01912v1.pdf
doi: nan
summary:
  Using realistic air flow simulation, we model droplet dispersion from coughing and study the transmission risk related to SARS-CoV-2. Notably, numerical methods, such as Computational Fluid Dynamics (CFD) based on Reynolds Averaged Navier-Stokes (RANS) turbulence models 31 produce high resolution flow fields and concentration data, 32 which not only compensate for slow instrumental speeds of analytical techniques, 25 but are also adaptable to different environments and scenarios, such as passengers in an aircraft cabin, 33 and more recently, a cough dispersion study in an outdoor environment under significant wind speeds, 34 whose results are useful in integrated transmission modeling. As detailed in the Supplementary Information, the model cough is inclined downwards at an average of 27·5°, 37 follows a characteristic air flow pattern 33,37 at breath temperature of 36°C, and emits a cluster of droplets with a standard size distribution 11, 38 and viral loading 39 

abstract:
  The Covid-19 pandemic has focused attention on airborne transmission of viruses. Using realistic air flow simulation, we model droplet dispersion from coughing and study the transmission risk related to SARS-CoV-2. Although most airborne droplets are 8-16 $mu$m in diameter, the droplets with the highest transmission potential are, in fact, 32-40 $mu$m. Use of face masks is therefore recommended for both personal and social protection. We found social distancing effective at reducing transmission potential across all droplet sizes. However, the presence of a human body 1 m away modifies the aerodynamics so that downstream droplet dispersion is enhanced, which has implications on safe distancing in queues. Based on median viral load, we found that an average of 0.55 viral copies is inhaled at 1 m distance per cough. Droplet evaporation results in significant reduction in droplet counts, but airborne transmission remains possible even under low humidity conditions.


id: cord-253252-s8fm5rfa
author: Jayaweera, Mahesh
date: 2020-06-13
txt: ./txt/cord-253252-s8fm5rfa.txt
cache: ./cache/cord-253252-s8fm5rfa.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32569870/
doi: 10.1016/j.envres.2020.109819
summary:
  This review paper intends to outline the literature concerning the transmission of viral-laden droplets and aerosols in different environmental settings and demonstrates the behavior of droplets and aerosols resulted from a cough-jet of an infected person in various confined spaces. There have been myriads of hypotheses corroborating that certain threshold levels of humidity, temperature, sunlight, and ventilation will speed up the virus-laden droplet and aerosol transmission, aggravating the spread of the SARS-CoV disease (Morawska, 2006) . Nevertheless, the effectiveness of the use of masks for the control of SARS-CoV-2-laden aerosol transmission from an infected person to a susceptible host is uncertain and not fully conceivable. Researchers have speculated that both droplets and aerosols generated from non-violent and violent expirations of SARS-CoV-2-infected people may be responsible for the nonnosocomial and nosocomial transmission of COVID-19 disease.

title:
  Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy

abstract:
  The practice of social distancing and wearing masks has been popular worldwide in combating the contraction of COVID-19. Undeniably, although such practices help control the COVID-19 pandemic to a greater extent, the complete control of viral-laden droplet and aerosol transmission by such practices is poorly understood. This review paper intends to outline the literature concerning the transmission of viral-laden droplets and aerosols in different environmental settings and demonstrates the behavior of droplets and aerosols resulted from a cough-jet of an infected person in various confined spaces. The case studies that have come out in different countries have, with prima facie evidence, manifested that the airborne transmission plays a profound role in contracting susceptible hosts. Interestingly, the nosocomial transmission by airborne SARS-CoV-2 viral-laden aerosols in healthcare facilities may be plausible. Hence, clearly defined, science-based administrative, clinical, and physical measures are of paramount importance to eradicate the COVID-19 pandemic from the world.


id: cord-254894-ta7hebbg
author: Balachandar, S.
date: 2020-09-04
txt: ./txt/cord-254894-ta7hebbg.txt
cache: ./cache/cord-254894-ta7hebbg.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/S0301932220305498
doi: 10.1016/j.ijmultiphaseflow.2020.103439
summary:
  In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. (ii) A first-order mathematical framework that describes the evolution of the cloud of respiratory droplets and their conversion to droplet nuclei, as a function of time, and (iii) A simple description of the inhalability of the aerosols along with the corresponding evaluation of the effectiveness of different masks based on existing data reported to date.

title:
  Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

abstract:
  COVID-19 pandemic has strikingly demonstrated how important it is to develop fundamental knowledge related to generation, transport and inhalation of pathogen-laden droplets and their subsequent possible fate as airborne particles, or aerosols, in the context of human to human transmission. It is also increasingly clear that airborne transmission is an important contributor to rapid spreading of the disease. In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. A simple model for the time evolution of droplet/aerosol concentration is presented based on a theoretical analysis of the relevant physical processes. The modeling framework along with detailed experiments and simulations can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in a number of environmental conditions, as humid or dry atmosphere, confined or open environment. Although a number of questions remain open on the physics of evaporation and coupling with persistence of the virus, it is clear that with a more reliable understanding of the underlying flow physics of virus transmission one can set the foundation for an improved methodology in designing case-specific social distancing and infection control guidelines.


id: cord-255084-qav7yb0p
author: Li, Xiangdong
date: 2018-01-15
txt: ./txt/cord-255084-qav7yb0p.txt
cache: ./cache/cord-255084-qav7yb0p.txt
extension: .txt
mime: text/plain
url: https://www.sciencedirect.com/science/article/pii/S0360132317305322
doi: 10.1016/j.buildenv.2017.11.025
summary:
  The approach is featured with a continuity equation being explicitly solved for water vapor, which allows comprehensively considering the effects of inhomogeneous humidity field on droplets evaporation and movement. The study also revealed that due to the droplet size reduction induced by evaporation, both the number density of airborne droplets and mass concentration of inhalable pathogens remarkably increased, which can result in a higher risk of infection. Apart from that, many other factors including the mass of exhaled droplets, the ambient temperature and humidity could have significant effects on the process of droplet evaporation, resulting in different time-size correlation and droplet dispersion trajectories. Comparatively, the time-dependent size of the 112-μm droplets was not significantly affected by the inhomogeneous humidity field, probably because the travelling speed of this group of droplets was larger than that of vapor dispersion (refer to Figs.

title:
  Modelling of evaporation of cough droplets in inhomogeneous humidity fields using the multi-component Eulerian-Lagrangian approach

abstract:
  This study employed a multi-component Eulerian-Lagrangian approach to model the evaporation and dispersion of cough droplets in quiescent air. The approach is featured with a continuity equation being explicitly solved for water vapor, which allows comprehensively considering the effects of inhomogeneous humidity field on droplets evaporation and movement. The computational fluid dynamics (CFD) computations based on the approach achieved a satisfactory agreement with the theoretical models reported in the literature. The results demonstrated that the evaporation-generated vapor and super-saturated wet air exhaled from the respiratory tracks forms a “vapor plume” in front of the respiratory track opening, which, despite the short life time, significantly impedes the evaporation of the droplets captured in it. The study also revealed that due to the droplet size reduction induced by evaporation, both the number density of airborne droplets and mass concentration of inhalable pathogens remarkably increased, which can result in a higher risk of infection. Parametric studies were finally conducted to evaluate the factors affecting droplet evaporation. SUMMARY: The study demonstrated the importance of considering inhomogeneous humidity field when modelling the evaporation and dispersion of cough droplets. The multi-component Eulerian-Lagrangian model presented in this study provides a comprehensive approach to address different influential factors in a wide parametric range, which will enhance the assessment of the health risks associated with droplet exposure.


id: cord-255770-gbhjke93
title: What ENT doctors should know about COVID‐19 contagion risks
author: Meccariello, Giuseppe
date: 2020-04-24
txt: ./txt/cord-255770-gbhjke93.txt
cache: ./cache/cord-255770-gbhjke93.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32329539/
doi: 10.1002/hed.26190
abstract: nan
summary:
  A general consensus exists on coronavirus diffusion by droplet transmission, especially the aerosolization during hospital procedures like intubation or bronchoscopy might represent a big concern, exposing other patients and healthcare staff to an increased risk of infection. Sore throat with or without fever, sneezing, hoarseness may be prodromic symptoms of a COVID-19 infection in the incubation period. Direct contact of droplet spray produced by coughing, sneezing, or talking involves relatively large droplets containing organisms and requires close contact usually within 1 m. Moreover, the total number of droplets generated during sneeze is also larger than that of other respiratory activities. The high-speed airflow and corresponding turbulence produced by sneeze may also lead to a large number of droplets, that is, the number of the droplets generated by sneeze is about 18 times larger than that of cough. SARS-CoV-2 viral load in upper respiratory specimens of infected patients


id: cord-258304-86gqxajw
title: Droplets and Aerosols generated by singing and the risk of COVID-19 for choirs
author: Bahl, Prateek
date: 2020-09-18
txt: ./txt/cord-258304-86gqxajw.txt
cache: ./cache/cord-258304-86gqxajw.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32945338/
doi: 10.1093/cid/ciaa1241
summary:
  title: Droplets and Aerosols generated by singing and the risk of COVID-19 for choirs The results of detailed particle tracking (in supplementary video) reveals that the maximum velocity of droplets expelled, specifically for certain syllables such as ''do'', ''fa'' and ''ti'', is approx. Figure 2c shows the velocity distribution of droplets that are visible while the subject was singing syllable ''sol'' & ''la'' and the direction in which these droplets are moving. Nevertheless, the droplets observed do not appear to be settling down rapidly and without adequate ventilation, these droplets can potentially saturate the indoor environment which can likely explain the very high attack rates of COVID-19 seen in choirs in the US and Europe (almost 87% in Skagit County, Washington) [1] . We note the present study only provides visual evidence of the droplets and aerosols expelled during singing and compare the associated velocities and directions with speaking and coughing.

abstract:
  Choral singing has become a major risk during COVID-19 pandemic due to high infection rates. Our visualisation and velocimetry results reveal that majority of droplets expelled during singing follow the ambient airflow pattern. These results points toward the possibility of COVID-19 spread by small airborne droplets during singing.


id: cord-263644-rg00br0d
title: Emission strength of airborne pathogens during toilet flushing
author: Lai, A. C. K.
date: 2017-08-14
txt: ./txt/cord-263644-rg00br0d.txt
cache: ./cache/cord-263644-rg00br0d.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/28683156/
doi: 10.1111/ina.12406
summary:
  This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom‐built toilet under a controlled environment. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=−0.919, P<.001; LP, r=−0.936, P<.001; HT, r=−0.967, P<.05) in the different conditions then tested. A significant association between bacterial emission strength at different degrees of flushing energy and flushing systems was reported in a recent study focusing on the initial droplet size distribution generated by flushing an experimental toilet system with various flushing mechanisms. Parameters such as water pressure, tank height, and bacterial size were varied, and the correlations between airborne droplet concentration and bacterial emission strength were investigated.

abstract:
  The flushing of toilets generates contaminated aerosols, the transmission of which may cause the spread of disease, particularly in the immunocompromised or the elderly. This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom‐built toilet under a controlled environment. Flushing was activated by a flushometer operated at two pressure levels, 400 kPa (high pressure [HP]) and 200 kPa (low pressure [LP]), and by a water cistern tank placed 95 cm (high tank [HT]) and 46 cm (low tank [LT]) above the toilet seat. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=−0.919, P<.001; LP, r=−0.936, P<.001; HT, r=−0.967, P<.05) in the different conditions then tested. The emission strength in the HP condition was statistically greater than that in the LP condition, whereas the cistern tank system produced less emissions than the flushometer system, and tank height was not found to be a sensitive parameter.


id: cord-271822-ohkki0ke
title: Visualizing the effectiveness of face masks in obstructing respiratory jets
author: Verma, Siddhartha
date: 2020-06-01
txt: ./txt/cord-271822-ohkki0ke.txt
cache: ./cache/cord-271822-ohkki0ke.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1063/5.0016018
doi: 10.1063/5.0016018
summary:
  We use qualitative visualizations of emulated coughs and sneezes to examine how materialand design-choices impact the extent to which droplet-laden respiratory jets are blocked. We outline the procedure for setting up simple visualization experiments using easily available materials, which may help healthcare professionals, medical researchers, and manufacturers in assessing the effectiveness of face masks and other personal protective equipment qualitatively. 7 The rationale behind the recommendation for using masks or other face coverings is to reduce the risk of cross-infection via the transmission of respiratory droplets from infected to healthy individuals. 8, 9 The pathogen responsible for COVID-19 is found primarily in respiratory droplets that are expelled by infected individuals during coughing, sneezing, or even talking and breathing. Various studies have investigated the effectiveness of medical-grade face masks and other personal protective equipment (PPE) in reducing the possibility of cross-infection via these droplets.

abstract:
  The use of face masks in public settings has been widely recommended by public health officials during the current COVID-19 pandemic. The masks help mitigate the risk of cross-infection via respiratory droplets; however, there are no specific guidelines on mask materials and designs that are most effective in minimizing droplet dispersal. While there have been prior studies on the performance of medical-grade masks, there are insufficient data on cloth-based coverings, which are being used by a vast majority of the general public. We use qualitative visualizations of emulated coughs and sneezes to examine how material- and design-choices impact the extent to which droplet-laden respiratory jets are blocked. Loosely folded face masks and bandana-style coverings provide minimal stopping-capability for the smallest aerosolized respiratory droplets. Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks, proved to be the most effective in reducing droplet dispersal. These masks were able to curtail the speed and range of the respiratory jets significantly, albeit with some leakage through the mask material and from small gaps along the edges. Importantly, uncovered emulated coughs were able to travel notably farther than the currently recommended 6-ft distancing guideline. We outline the procedure for setting up simple visualization experiments using easily available materials, which may help healthcare professionals, medical researchers, and manufacturers in assessing the effectiveness of face masks and other personal protective equipment qualitatively.


id: cord-274083-6vln3erl
title: Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface
author: Bhardwaj, Rajneesh
date: 2020-06-01
txt: ./txt/cord-274083-6vln3erl.txt
cache: ./cache/cord-274083-6vln3erl.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32574230/
doi: 10.1063/5.0012009
summary:
  Drying of the droplet is predicted by using a diffusion-limited evaporation model for a sessile droplet placed on a partially wetted surface with a pinned contact line. We consider diffusion-limited, quasi-steady evaporation of a sessile droplet with a pinned contact line on a partially wetted surface (Fig. 2) . The mass lost rate (kg/s) of an evaporating sessile droplet is expressed as follows: 12 where H and θ are relative humidity and static contact angle, respectively. (8) and (10) Second, we present the effect of ambient temperature, surface wettability, and relative humidity on the drying time of the droplet. To determine the likelihood of the droplet and the virus on the surface, we find the mean and standard deviation of the probability density function (PDF) of the normal distribution of the droplet drying times for different cases of ambient temperature, contact angle, and relative humidity.

abstract:
  We predict and analyze the drying time of respiratory droplets from a COVID-19 infected subject, which is a crucial time to infect another subject. Drying of the droplet is predicted by using a diffusion-limited evaporation model for a sessile droplet placed on a partially wetted surface with a pinned contact line. The variation in droplet volume, contact angle, ambient temperature, and humidity are considered. We analyze the chances of the survival of the virus present in the droplet based on the lifetime of the droplets under several conditions and find that the chances of the survival of the virus are strongly affected by each of these parameters. The magnitude of shear stress inside the droplet computed using the model is not large enough to obliterate the virus. We also explore the relationship between the drying time of a droplet and the growth rate of the spread of COVID-19 in five different cities and find that they are weakly correlated.


id: cord-274781-tmc31aa6
author: Cummins, C. P.
date: 2020-08-01
txt: ./txt/cord-274781-tmc31aa6.txt
cache: ./cache/cord-274781-tmc31aa6.txt
extension: .txt
mime: text/plain
url: https://arxiv.org/pdf/2007.05298v2.pdf
doi: 10.1063/5.0021427
summary:
  We find that, in the absence of gravity, there are two distinct behaviors for the droplets: small droplets cannot go further than a specific distance, which we determine analytically, from the source before getting pulled into the sink. The transport of inertial particles in fluid flows occurs in many problems arising in engineering and biology, such as the build-up of microplastics in the ocean 1 and respiratory virus transmission through tract droplets. 17 Such a flow could represent the trajectories of water droplets emitted from coughing, sneezing, [2] [3] [4] or breathing and in the presence of extraction, such as an air-conditioning unit or air current. We are interested in where the flow field changes direction, since this indicates the maximum distance the droplets emitted at the source can travel before moving toward the sink. We model the situation as a point source emitting droplets of various sizes in the presence of gravitational forces and compute the maximum horizontal distance traveled by these droplets.

title:
  The dispersion of spherical droplets in source–sink flows and their relevance to the COVID-19 pandemic

abstract:
  In this paper, we investigate the dynamics of spherical droplets in the presence of a source–sink pair flow field. The dynamics of the droplets is governed by the Maxey–Riley equation with the Basset–Boussinesq history term neglected. We find that, in the absence of gravity, there are two distinct behaviors for the droplets: small droplets cannot go further than a specific distance, which we determine analytically, from the source before getting pulled into the sink. Larger droplets can travel further from the source before getting pulled into the sink by virtue of their larger inertia, and their maximum traveled distance is determined analytically. We investigate the effects of gravity, and we find that there are three distinct droplet behaviors categorized by their relative sizes: small, intermediate-sized, and large. Counterintuitively, we find that the droplets with a minimum horizontal range are neither small nor large, but of intermediate size. Furthermore, we show that in conditions of regular human respiration, these intermediate-sized droplets range in size from a few μm to a few hundred μm. The result that such droplets have a very short range could have important implications for the interpretation of existing data on droplet dispersion.


id: cord-275303-8mj8gjv9
title: Modeling the role of respiratory droplets in Covid-19 type pandemics
author: Chaudhuri, Swetaprovo
date: 2020-06-01
url: https://doi.org/10.1063/5.0015984
doi: 10.1063/5.0015984
abstract:
  In this paper, we develop a first principles model that connects respiratory droplet physics with the evolution of a pandemic such as the ongoing Covid-19. The model has two parts. First, we model the growth rate of the infected population based on a reaction mechanism. The advantage of modeling the pandemic using the reaction mechanism is that the rate constants have sound physical interpretation. The infection rate constant is derived using collision rate theory and shown to be a function of the respiratory droplet lifetime. In the second part, we have emulated the respiratory droplets responsible for disease transmission as salt solution droplets and computed their evaporation time, accounting for droplet cooling, heat and mass transfer, and finally, crystallization of the dissolved salt. The model output favourably compares with the experimentally obtained evaporation characteristics of levitated droplets of pure water and salt solution, respectively, ensuring fidelity of the model. The droplet evaporation/desiccation time is, indeed, dependent on ambient temperature and is also a strong function of relative humidity. The multi-scale model thus developed and the firm theoretical underpinning that connects the two scales—macro-scale pandemic dynamics and micro-scale droplet physics—thus could emerge as a powerful tool in elucidating the role of environmental factors on infection spread through respiratory droplets.


id: cord-276649-3zl3pm79
author: Tan, Vanessa Y. J.
date: 2020-07-04
txt: ./txt/cord-276649-3zl3pm79.txt
cache: ./cache/cord-276649-3zl3pm79.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1002/hed.26347
doi: 10.1002/hed.26347
summary:
  We outline the following recommendations: pull the face mask down partially and keep the mouth covered, only allowing nasal access during nasoendoscopy; avoid nasal sprays if possible; if nasal sprays are used, procedurists should be in full personal protective equipment prior to using the spray; withdrawal of swabs and scopes should be performed in a slow and controlled fashion to reduce potential dispersion of droplets when the capillary bridge of mucus breaks up. We outline the following recommendations: pull the face mask down partially and keep the mouth covered, only allowing nasal access during nasoendoscopy; avoid nasal sprays if possible; if nasal sprays are used, procedurists should be in full personal protective equipment prior to using the spray; withdrawal of swabs and scopes should be performed in a slow and controlled fashion to reduce potential dispersion of droplets when the capillary bridge of mucus breaks up.

title:
  Respiratory droplet generation and dispersal during nasoendoscopy and upper respiratory swab testing

abstract:
  Respiratory particle generation and dispersal during nasoendoscopy and swab testing is studied with high‐speed video and laser light illumination. Video analysis reveals droplet formation in three manoeuvres during nasoendoscopy ‐ sneezing, vocalization, and nasal decongestion spray. A capillary bridge of mucus can be seen when a nasoendoscope exits wet nares. No droplet formation is seen during oral and nasopharyngeal swab testing. We outline the following recommendations: pull the face mask down partially and keep the mouth covered, only allowing nasal access during nasoendoscopy; avoid nasal sprays if possible; if nasal sprays are used, procedurists should be in full personal protective equipment prior to using the spray; withdrawal of swabs and scopes should be performed in a slow and controlled fashion to reduce potential dispersion of droplets when the capillary bridge of mucus breaks up.


id: cord-290277-ndfoppoq
title: Airborne or droplet precautions for health workers treating COVID-19?
author: Bahl, Prateek
date: 2020-04-16
txt: ./txt/cord-290277-ndfoppoq.txt
cache: ./cache/cord-290277-ndfoppoq.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1093/infdis/jiaa189
doi: 10.1093/infdis/jiaa189
summary:
  World Health Organization (WHO) has issued guidelines for contact and droplet precautions for Healthcare Workers (HCWs) caring for suspected COVID-19 patients, whilst the US Centre for Disease Control (CDC) has recommended airborne precautions. We aimed to review the evidence for horizontal distance travelled by droplets and the guidelines issued by the World Health Organization (WHO), US Center for Diseases Control (CDC) and European Centre for Disease Prevention and Control (ECDC) on respiratory protection for COVID-19. We aimed to review the evidence supporting the rule of 1 m (≈3 ft) spatial separation for droplet precautions in the context of guidelines issued by the World Health Organization (WHO), US Center for Diseases Control (CDC) and European Centre for Disease Prevention and Control (ECDC) for HCWs on respiratory protection for COVID-19. Interim Infection Prevention and Control Recommendations for Hospitalized Patients with Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

abstract:
  Cases of COVID-19 have been reported in over 200 countries. Thousands of health workers have been infected and outbreaks have occurred in hospitals, aged care facilities and prisons. World Health Organization (WHO) has issued guidelines for contact and droplet precautions for Healthcare Workers (HCWs) caring for suspected COVID-19 patients, whilst the US Centre for Disease Control (CDC) has recommended airborne precautions. The 1 – 2 m (≈3 – 6 ft) rule of spatial separation is central to droplet precautions and assumes large droplets do not travel further than 2 m (≈6 ft). We aimed to review the evidence for horizontal distance travelled by droplets and the guidelines issued by the World Health Organization (WHO), US Center for Diseases Control (CDC) and European Centre for Disease Prevention and Control (ECDC) on respiratory protection for COVID-19. We found that the evidence base for current guidelines is sparse, and the available data do not support the 1 – 2 m (≈3 – 6 ft) rule of spatial separation. Of ten studies on horizontal droplet distance, eight showed droplets travel more than 2 m (≈6 ft), in some cases more than 8 meters (≈26 ft). Several studies of SARS-CoV-2 support aerosol transmission and one study documented virus at a distance of 4 meters (≈13 ft) from the patient. Moreover, evidence suggests infections cannot neatly be separated into the dichotomy of droplet versus airborne transmission routes. Available studies also show that SARS-CoV-2 can be detected in the air, 3 hours after aeroslisation. The weight of combined evidence supports airborne precautions for the occupational health and safety of health workers treating patients with COVID-19.


id: cord-291836-dlsas702
title: Transmission of pathogen-laden expiratory droplets in a coach bus
author: Yang, Xia
date: 2020-04-12
url: https://www.ncbi.nlm.nih.gov/pubmed/32361671/
doi: 10.1016/j.jhazmat.2020.122609
abstract:
  Abstract Droplet dispersion carrying viruses/bacteria in enclosed/crowded buses may induce transmissions of respiratory infectious diseases, but the influencing mechanisms have been rarely investigated. By conducting high-resolution CFD simulations, this paper investigates the evaporation and transport of solid-liquid mixed droplets (initial diameter 10 μm and 50 μm, solid to liquid ratio is 1:9) exhaled in a coach bus with 14 thermal manikins. Five air-conditioning supply directions and ambient relative humidity (RH = 35% and 95%) are considered. Results show that ventilation effectiveness, RH and initial droplet size significantly influence droplet transmissions in coach bus. 50 μm droplets tend to evaporate completely within 1.8 s and 7 s as RH = 35% and 95% respectively, while 0.2 s or less for 10 μm droplets. Thus 10 μm droplets diffuse farther with wider range than 50 μm droplets which tend to deposit more on surfaces. Droplet dispersion pattern differs due to various interactions of gravity, ventilation flows and the upward thermal body plume. The fractions of droplets suspended in air, deposited on wall surfaces are quantified. This study implies high RH, backward supply direction and passengers sitting at nonadjacent seats can effectively reduce infection risk of droplet transmission in buses. Besides taking masks, regular cleaning is also recommended since 85%-100% of droplets deposit on object surfaces.


id: cord-293097-poh1y6o7
author: V, Antony Aroul Raj
date: 2020-07-02
txt: ./txt/cord-293097-poh1y6o7.txt
cache: ./cache/cord-293097-poh1y6o7.txt
extension: .txt
mime: text/plain
url: https://www.sciencedirect.com/science/article/pii/S2210670720305928?v=s5
doi: 10.1016/j.scs.2020.102371
summary:
  This concept is assessed using four major parameters such as population density, climate severity, the volume of indoor spaces, and air-conditioning usage which affect the infection spread and mortality using the data available for various states of India. Hence the major objective of the present work is to propose the mechanism of virus spread under various climates and the indoor environment conditions maintained through the existing theory of respiratory droplet drying. Further, it is aimed to perform a statistical study on the dependence of mortality and infection in the Indian States with respect to four major parameters such as population density, climate severity, volume of indoor spaces, and air-conditioning usage based on monthly data for March and April. In an environment with low humidity and low temperature, due to combined high heat and mass transfer potential leads to fast drying and size reduction of the respiratory droplets and the virus is almost active in all the locations.

title:
  The contribution of dry indoor built environment on the spread of Coronavirus: Data from various Indian states

abstract:
  Coronavirus spread is more serious in urban metropolitan cities compared to rural areas. It is observed from the data on the infection rate available in the various sources that the cold and dry conditions accelerate the spread of coronavirus. In the present work, the existing theory of respiratory droplet drying is used to propose the mechanism of virus spread under various climates and the indoor environment conditions which plays a greater role in the virus spread. This concept is assessed using four major parameters such as population density, climate severity, the volume of indoor spaces, and air-conditioning usage which affect the infection spread and mortality using the data available for various states of India. Further, it is analysed using the data from various states in India along with the respective climatic conditions. It is found that under some indoor scenarios, the coronaviruses present in the respiratory droplets become active due to size reduction that occurs both in sessile and airborne droplet nuclei causing an increase in the spread. Understanding this mechanism will be very useful to take the necessary steps to reduce the rate of transmission by initiating corrective measures and maintaining the required conditions in the indoor built environment.


id: cord-298227-av1ev8ta
title: Fundamental protective mechanisms of face masks against droplet infections
author: Kähler, Christian J.
date: 2020-06-28
url: https://www.sciencedirect.com/science/article/pii/S0021850220301063?v=s5
doi: 10.1016/j.jaerosci.2020.105617
abstract:
  Many governments have instructed the population to wear simple mouth-and-nose covers or surgical face masks to protect themselves from droplet infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in public. However, the basic protection mechanisms and benefits of these masks remain controversial. Therefore, the aim of this work is to show from a fluid physics point of view under which circumstances these masks can protect against droplet infection. First of all, we show that the masks protect people in the surrounding area quite well, since the flow resistance of the face masks effectively prevents the spread of exhaled air, e.g. when breathing, speaking, singing, coughing and sneezing. Secondly, we provide visual evidence that typical household materials used by the population to make masks do not provide highly efficient protection against respirable particles and droplets with a diameter of 0.3–2 μm as they pass through the materials largely unfiltered. According to our tests, only vacuum cleaner bags with fine dust filters show a comparable or even better filtering effect than commercial particle filtering FFP2/N95/KN95 half masks. Thirdly, we show that even simple mouth-and-nose covers made of good filter material cannot reliably protect against droplet infection in contaminated ambient air, since most of the air flows through gaps at the edge of the masks. Only a close-fitting, particle-filtering respirator without an outlet valve offers good self-protection and protection against droplet infection. Nevertheless, wearing simple homemade or surgical face masks in public is highly recommended if no particle filtrating respiratory mask is available. Firstly, because they protect against habitual contact of the face with the hands and thus serve as self-protection against contact infection. Secondly, because the flow resistance of the masks ensures that the air stays close to the head when breathing, speaking, singing, coughing and sneezing, thus protecting other people if they have sufficient distance from each other. However, if the distance rules cannot be observed and the risk of inhalation-based infection becomes high because many people in the vicinity are infectious and the air exchange rate is small, improved filtration efficiency masks are needed, to take full advantage of the three fundamental protective mechanisms these masks provide.


id: cord-298461-tyhtdawb
title: COVID-19: Effects of weather conditions on the propagation of respiratory droplets
author: Zhao, L.
date: 2020-05-25
url: https://doi.org/10.1101/2020.05.24.20111963
doi: 10.1101/2020.05.24.20111963
abstract:
  As the number of confirmed cases of Coronavirus disease 2019 (COVID-19) continues to increase, there has been a rising concern regarding the effect of weather conditions, especially over the upcoming summer, on the transmission of this disease. In this study, we assess the transmission of COVID-19 under different weather conditions by investigating the propagation of infectious respiratory droplets. A comprehensive mathematical model is established to explore their evaporation, heat transfer and kinematics under different temperature, humidity and ventilation conditions. The transmitting pathway of COVID-19 through respiratory droplets is divided into short-range droplet contacts and long-range aerosol exposure. We show that the effect of weather conditions is not monotonic: low temperature and high humidity facilitate droplet contact transmission, while high temperature and low humidity promote the formation of aerosol particles and accumulation of particles with a diameter of 2.5 m or less (PM2.5). Our model suggests that the 6 ft of social distance recommended by the Center for Disease Control and Prevention (CDC) may be insufficient in certain environmental conditions, as the droplet spreading distance can be as long as 6 m (19.7 ft) in cold and humid weather. The results of this study suggest that the current pandemic may not ebb in the summer of the northern hemisphere without proper intervention, as there is an increasing chance of aerosol transmission. We also emphasize that the meticulous design of building ventilation systems is critical in containing both the droplet contact infections and aerosol exposures.


id: cord-301721-31a2q3ad
author: Balachandar, S.
date: 2020-09-01
txt: ./txt/cord-301721-31a2q3ad.txt
cache: ./cache/cord-301721-31a2q3ad.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1101/2020.08.28.20183814
doi: 10.1101/2020.08.28.20183814
summary:
  In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. But as the puff of air and the droplets move forward, the droplet Reynolds number rapidly decreases for the following reasons: (i) as will be seen in section 4.1 the puff velocity decreases due to entrainment and drag, (ii) as will be seen in section 4.2.1 the droplet diameter will decrease rapidly due to evaporation, (iii) as will be seen in section 4.2.2 the time scale τ V on which the droplet accelerates to the surrounding fluid velocity of the puff is quite small, and (iv) very large droplets quickly fall out of the puff and do not form part of airborne droplets. It should again be emphasized that the temperature difference between the puff fluid containing the droplet nuclei cloud and the ambient air may induce buoyancy effects, which for model simplicity will be taken into account as part of turbulent dispersion.

title:
  Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

abstract:
  COVID-19 pandemic has strikingly demonstrated how important it is to develop fundamental knowledge related to generation, transport and inhalation of pathogen-laden droplets and their subsequent possible fate as airborne particles, or aerosols, in the context of human to human transmission. It is also increasingly clear that airborne transmission is an important contributor to rapid spreading of the disease. In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. A simple model for the time evolution of droplet/aerosol concentration is presented based on a theoretical analysis of the relevant physical processes. The modeling framework along with detailed experiments and simulations can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in a number of environmental conditions, as humid or dry atmosphere, confined or open environment. Although a number of questions remain open on the physics of evaporation and coupling with persistence of the virus, it is clear that with a more reliable understanding of the underlying flow physics of virus transmission one can set the foundation for an improved methodology in designing case-specific social distancing and infection control guidelines.


id: cord-306861-qcctchsk
author: Chen, Xiaole
date: 2020-07-24
txt: ./txt/cord-306861-qcctchsk.txt
cache: ./cache/cord-306861-qcctchsk.txt
extension: .txt
mime: text/plain
url: https://www.sciencedirect.com/science/article/pii/S0021850220301142?v=s5
doi: 10.1016/j.jaerosci.2020.105626
summary:
  Using a validated computational model, the transport, evaporation, hygroscopic growth, and deposition of multi-component droplets were simulated in a simplified airway geometry. Numerical results indicate that the droplet/particle-vapor interaction and the heat and mass transfer of the mucus-tissue layer must be considered in the computational lung aerosol dynamics study, since they can significantly influence the precise predictions of the aerosol transport and deposition. If the more realistic thermal boundary (Chen, 11 al., 2018; Wu, et al., 2014) and indoor air conditions (McFadden Jr, et al., 1985) are 12 considered, higher inhalation flow rate also has a stronger cooling effect on the 13 mucus-tissue layer, which further affects the mucus evaporation. Therefore, the 14 transport, hygroscopic growth, and deposition of multi-component droplets have not 15 been investigated under different inhalation flow rate conditions, when employing the 16 more realistic thermal boundary conditions.

title:
  Modeling of the transport, hygroscopic growth, and deposition of multi-component droplets in a simplified airway with realistic thermal boundary conditions

abstract:
  Accurate predictions of the droplet transport, evolution, and deposition in human airways are critical for the quantitative analysis of the health risks due to the exposure to the airborne pollutant or virus transmission. The droplet/particle-vapor interaction, i.e., the evaporation or condensation of the multi-component droplet/particle, is one of the key mechanisms that need to be precisely modeled. Using a validated computational model, the transport, evaporation, hygroscopic growth, and deposition of multi-component droplets were simulated in a simplified airway geometry. A mucus-tissue layer is explicitly modeled in the airway geometry to describe mucus evaporation and heat transfer. Pulmonary flow and aerosol dynamics patterns associated with different inhalation flow rates are visualized and compared. Investigated variables include temperature distributions, relative humidity (RH) distributions, deposition efficiencies, droplet/particle distributions, and droplet growth ratio distributions. Numerical results indicate that the droplet/particle-vapor interaction and the heat and mass transfer of the mucus-tissue layer must be considered in the computational lung aerosol dynamics study, since they can significantly influence the precise predictions of the aerosol transport and deposition. Furthermore, the modeling framework in this study is ready to be expanded to predict transport dynamics of cough/sneeze droplets starting from their generation and transmission in the indoor environment to the deposition in the human respiratory system.


id: cord-307264-l13gyl94
title: Physics of virus transmission by speaking droplets
author: Netz, Roland R.
date: 2020-10-13
txt: ./txt/cord-307264-l13gyl94.txt
cache: ./cache/cord-307264-l13gyl94.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1073/pnas.2011889117
doi: 10.1073/pnas.2011889117
summary:
  Calculations with these equations provide a straightforward way of determining whether emitted droplets remain airborne or rapidly fall to the ground, after accounting for the decrease in droplet size from water evaporation. Calculations with these equations provide a straightforward way of determining whether emitted droplets remain airborne or rapidly fall to the ground, after accounting for the decrease in droplet size from water evaporation. At a relative humidity of 50%, for example, droplets with initial radii larger than about 50 μm rapidly fall to the ground, while smaller, potentially virus-containing droplets shrink in size from water evaporation and remain airborne for many minutes. At a relative humidity of 50%, for example, droplets with initial radii larger than about 50 μm rapidly fall to the ground, while smaller, potentially virus-containing droplets shrink in size from water evaporation and remain airborne for many minutes.

abstract:
  To make the physics of person-to-person virus transmission from emitted droplets of oral fluid while speaking easily understood, we present simple and transparent algebraic equations that capture the essential physics of the problem. Calculations with these equations provide a straightforward way of determining whether emitted droplets remain airborne or rapidly fall to the ground, after accounting for the decrease in droplet size from water evaporation. At a relative humidity of 50%, for example, droplets with initial radii larger than about 50 μm rapidly fall to the ground, while smaller, potentially virus-containing droplets shrink in size from water evaporation and remain airborne for many minutes. Estimates of airborne virion emission rates while speaking strongly support the proposal that mouth coverings can help contain the COVID-19 pandemic.


id: cord-307768-xx46w6dc
author: Ding, Yun
date: 2017-03-10
txt: ./txt/cord-307768-xx46w6dc.txt
cache: ./cache/cord-307768-xx46w6dc.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32214953/
doi: 10.1007/s10404-017-1889-4
summary:
  title: From single-molecule detection to next-generation sequencing: microfluidic droplets for high-throughput nucleic acid analysis Recent applications of such technologies to genetic analysis have suggested significant utility in low-cost, efficient and rapid workflows for DNA amplification, rare mutation detection, antibody screening and next-generation sequencing. 2003) , with the relative concentration of each reagent being defined by the Fig. 1 a Physical and chemical variables in droplet-based experiments: (1) Temperature can be controlled over wide ranges, enabling PCR in emulsions; (2) Hydrophobic substrates or ligands can be delivered through the oil phase into aqueous droplets; (3) Watersoluble components can be delivered through nanoscale droplets or swollen micelles, allowing the regulation of biochemical processes; (4) Internal pH can be altered, for example, by the delivery of acetic acid; (5) Photocaged substrates and ligands can be introduced into the droplets during emulsification and photoactivated at later times. Two recent studies describing single-cell RNA sequencing methods using droplet-based microfluidics [termed Drop-seq (Macosko et al.

title:
  From single-molecule detection to next-generation sequencing: microfluidic droplets for high-throughput nucleic acid analysis

abstract:
  Droplet-based microfluidic technologies have proved themselves to be of significant utility in the performance of high-throughput chemical and biological experiments. By encapsulating and isolating reagents within femtoliter–nanoliter droplet, millions of (bio) chemical reactions can be processed in a parallel fashion and on ultra-short timescales. Recent applications of such technologies to genetic analysis have suggested significant utility in low-cost, efficient and rapid workflows for DNA amplification, rare mutation detection, antibody screening and next-generation sequencing. To this end, we describe and highlight some of the most interesting recent developments and applications of droplet-based microfluidics in the broad area of nucleic acid analysis. In addition, we also present a cursory description of some of the most essential functional components, which allow the creation of integrated and complex workflows based on flowing streams of droplets.


id: cord-312236-8eaqn8eu
title: Study of expiratory droplet dispersion and transport using a new Eulerian modeling approach
author: Lai, Alvin C.K.
date: 2007-06-02
url: https://api.elsevier.com/content/article/pii/S1352231007005031
doi: 10.1016/j.atmosenv.2007.05.045
abstract:
  Understanding of droplet nuclei dispersion and transport characteristics can provide more engineering strategies to control transmission of airborne diseases. Droplet dispersion in a room under the conventional well-mixed and displacement ventilation is simulated. Two droplet nuclei sizes, 0.01 and 10 μm, are selected as they represent very fine and coarse droplets. The flow field is modeled using k–ε RNG model. A new Eulerian drift-flux methodology is employed to model droplet phase. Under the conventional ventilation scheme, both fine and coarse droplets are homogeneously dispersed within approximately 50 s. Droplet nuclei exhibit distinctive dispersion behavior, particularly for low airflow microenvironment. After 270 s of droplet emission, gravitational settling influences the dispersion for 10 μm droplets, and concentration gradient can still be observed for displacement ventilation.


id: cord-312708-9ywu6r2t
author: Sharma, Dhruv
date: 2020-05-19
txt: ./txt/cord-312708-9ywu6r2t.txt
cache: ./cache/cord-312708-9ywu6r2t.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1177/0194599820930245
doi: 10.1177/0194599820930245
summary:
  OBJECTIVE: The otolaryngology community has significant concerns regarding the spread of SARS-CoV-2 through droplet contamination and viral aerosolization during head and neck examinations and procedures. RESULTS: There were no fluorescein droplets or splatter contamination observed in the measured surgical field in any direction after myringotomy and insertion of ventilation tube. 7 As a result, the American Academy of Otolaryngology-Head and Neck Surgery has issued a position statement to limit elective procedures requiring interaction with upper airway mucosal surfaces or those with increased risk of aerosolization, which may include otologic procedures such as myringotomy and mastoidectomy. Since the upper respiratory tract harbors a high viral load, 3 otolaryngologists are vulnerable to SARS-CoV-2 transmission while performing head and neck procedures that utilize suction and powered instrumentation, such as the surgical drill, especially if they are doing so without appropriate protective personal equipment.

title:
  Cadaveric Simulation of Otologic Procedures: An Analysis of Droplet Splatter Patterns During the COVID-19 Pandemic

abstract:
  OBJECTIVE: The otolaryngology community has significant concerns regarding the spread of SARS-CoV-2 through droplet contamination and viral aerosolization during head and neck examinations and procedures. The objective of this study was to investigate the droplet and splatter contamination from common otologic procedures. STUDY DESIGN: Cadaver simulation series. SETTING: Dedicated surgical laboratory. METHODS: Two cadaver heads were prepped via bilateral middle cranial fossa approaches to the tegmen (n = 4). Fluorescein was instilled through a 4-mm burr hole drilled into the middle cranial fossa floor, and presence in the middle ear was confirmed via microscopic ear examination. Myringotomy with ventilation tube placement and mastoidectomy were performed, and the distribution and distance of resulting droplet splatter patterns were systematically evaluated. RESULTS: There were no fluorescein droplets or splatter contamination observed in the measured surgical field in any direction after myringotomy and insertion of ventilation tube. Gross contamination from the surgical site to 6 ft was noted after complete mastoidectomy, though, when performed in standard fashion. CONCLUSION: Our results show that there is no droplet generation during myringotomy with ventilation tube placement in an operating room setting. Mastoidectomy, however, showed gross contamination 3 to 6 ft away in all directions measured. Additionally, there was significantly more droplet and splatter generation to the left of the surgeon when measured at 1 and 3 ft as compared with all other measured directions.


id: cord-313636-kcjnjq52
title: Identifying the extent of oral fluid droplets on echocardiographic machine consoles in COVID-19 era
author: Kusunose, Kenya
date: 2020-09-18
txt: ./txt/cord-313636-kcjnjq52.txt
cache: ./cache/cord-313636-kcjnjq52.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32946008/
doi: 10.1007/s12574-020-00491-9
abstract: nan
summary:
  title: Identifying the extent of oral fluid droplets on echocardiographic machine consoles in COVID-19 era The aim of this study was to identify the extent of oral fluid droplet spread on echocardiographic machine consoles, after observers were speaking in English or Japanese. Two observers without surgical masks repeated the words "inhale, exhale, hold" (the words often used during examinations) in English and Japanese, in front of echocardiographic machine (EUB-7500, Hitachi Medical Corporation, Japan) after ingesting the liquid with volunteers lying on your left side echocardiography. It was also important that no droplets were detected on the console when surgical masks were worn in this setting, although it is unlikely that examinations would be performed with either the sonographer/cardiologist scanning or the patient not wearing a mask in the current COVID era. To the best of our knowledge, this is the first report to assess the spread of the droplets generated by speech on the surface of an echocardiographic machine using visualized methods.


id: cord-316129-mjg3un0l
author: Khamar, Pooja
date: 2020-07-13
txt: ./txt/cord-316129-mjg3un0l.txt
cache: ./cache/cord-316129-mjg3un0l.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32675657/
doi: 10.1097/j.jcrs.0000000000000326
summary:
  title: Aerosol and droplet creation during oscillatory motion of the microkeratome amidst COVID-19 and other infectious diseases METHOD: In an experimental setup, flap creation was performed on enucleated goat''s eyes (n = 8) mounted on a stand using One Use-Plus SBK Moria microkeratome (Moria SA) to assess the spread of aerosols and droplets using high-speed shadowgraphy. The maximum distance traversed was ∼1.8 m and ∼1.3 m assuming a constant airflow (setting of refractive surgery theater) and decaying jet condition (setting of an operating theater with air-handling unit), respectively. The maximum distance traversed was ∼1.8 m and ∼1.3 m assuming a constant airflow (setting of refractive surgery theater) and decaying jet condition (setting of an operating theater with air-handling unit), respectively. 13, 14 Therefore, we quantified the aerosol and droplet generation during flap creation using the Moria One Use-Plus SBK microkeratome (Moria SA) and assessed their trajectory using high-speed shadowgraphy and fluid mechanics principles.

title:
  Aerosol and droplet creation during oscillatory motion of the microkeratome amidst COVID-19 and other infectious diseases

abstract:
  PURPOSE: To quantify the atomization of liquid over the cornea during flap creation using microkeratome using high-speed shadowgraphy. SETTING: Laboratory investigational study. DESIGN: Laboratory study. METHOD: In an experimental setup, flap creation was performed on enucleated goat's eyes (n = 8) mounted on a stand using One Use-Plus SBK Moria microkeratome (Moria SA) to assess the spread of aerosols and droplets using high-speed shadowgraphy. Two conditions were computed. A constant airflow assumed uniform air velocity throughout the room. A decaying jet assumed that local air velocity at the site of measurements was smaller than the exit velocity from the air duct. RESULTS: With the advancement of the microkeratome across the wet corneal surface, the atomization of a balanced salt solution was recorded on shadowgraphy. The minimum droplet size was ∼90 μm. The maximum distance traversed was ∼1.8 m and ∼1.3 m assuming a constant airflow (setting of refractive surgery theater) and decaying jet condition (setting of an operating theater with air-handling unit), respectively. CONCLUSIONS: The microkeratome-assisted LASIK flap creation does seem to cause spread of droplets. The droplet diameters and velocities did not permit the formation of aerosols. Therefore, the risk of transmission of the virus to the surgeon and surgical personnel due to the microkeratome procedure seems to be low.


id: cord-318187-c59c9vi3
title: Numerical evaluation of spray position for improved nasal drug delivery
author: Basu, Saikat
date: 2020-06-29
url: https://www.ncbi.nlm.nih.gov/pubmed/32601278/
doi: 10.1038/s41598-020-66716-0
abstract:
  Topical intra-nasal sprays are amongst the most commonly prescribed therapeutic options for sinonasal diseases in humans. However, inconsistency and ambiguity in instructions show a lack of definitive knowledge on best spray use techniques. In this study, we have identified a new usage strategy for nasal sprays available over-the-counter, that registers an average 8-fold improvement in topical delivery of drugs at diseased sites, when compared to prevalent spray techniques. The protocol involves re-orienting the spray axis to harness inertial motion of particulates and has been developed using computational fluid dynamics simulations of respiratory airflow and droplet transport in medical imaging-based digital models. Simulated dose in representative models is validated through in vitro spray measurements in 3D-printed anatomic replicas using the gamma scintigraphy technique. This work breaks new ground in proposing an alternative user-friendly strategy that can significantly enhance topical delivery inside human nose. While these findings can eventually translate into personalized spray usage instructions and hence merit a change in nasal standard-of-care, this study also demonstrates how relatively simple engineering analysis tools can revolutionize everyday healthcare. Finally, with respiratory mucosa as the initial coronavirus infection site, our findings are relevant to intra-nasal vaccines that are in-development, to mitigate the COVID-19 pandemic.


id: cord-318835-sd9hbocg
title: Utility of patient face masks to limit droplet spread from simulated coughs at the slit lamp
author: Felfeli, Tina
date: 2020-07-27
txt: ./txt/cord-318835-sd9hbocg.txt
cache: ./cache/cord-318835-sd9hbocg.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/S000841822030630X
doi: 10.1016/j.jcjo.2020.06.010
abstract: nan
summary:
  title: Utility of patient face masks to limit droplet spread from simulated coughs at the slit lamp 3 Herein, we aimed to investigate how various scenarios of masks worn by patients can reduce the spread of respiratory droplets onto the examiner during a slit-lamp examination using a simulated patient cough. This simulation demonstrates that the use of slit-lamp breath shields and standard PPE for the examiner may reduce but does not eliminate the projection of droplets onto the examiner''s field, chest, shoulders, and arms (Fig. 1) . In the simulation involving the improperly positioned surgical mask, droplets were identified on the shoulders, arms, and gloves of the examiner as well as the slit lamp, floor, and walls. Our findings suggest that the use of a properly fitted mask on the patient as an adjunct to the current standard PPE used by the examiner, and the breath shield is essential for limiting droplet dissemination during slit-lamp examinations.


id: cord-319822-h1zm94p4
title: A physicist''s approach to COVID-19 transmission via expiratory droplets
author: Carelli, Pasquale
date: 2020-06-17
txt: ./txt/cord-319822-h1zm94p4.txt
cache: ./cache/cord-319822-h1zm94p4.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/S0306987720311853
doi: 10.1016/j.mehy.2020.109997
summary:
  My thesis is supported and described on the basis of a physicist''s model which studies the droplets behavior when emitted by the respiratory apparatus of an infected person, symptomatic or not. The intermediate dimensioned droplets are proved to be changed into aerosol, losing their water content and becoming seriously contagious, but in their initial phase they could be easily caught by a simple surgical mask. This habit, There are non doubts about the fact that expiratory particles transmit the pandemic, but we must make a coarse distinction among droplets and their dynamic evolutions when emitted by infected people. These droplets have a substantial viral load, they are quite numerous, some thousands of them can contain just one single virion each and they are probably the most contagious and dangerous elements[14]; if not stopped on time, they constitute the real element of airborne infection [15] .

abstract:
  In this paper, a physicist's approach is given to support the necessity to wear surgical masks during the COVID-19 pandemics; they have become compulsory in Eastern countries, while in Western countries they are still an optional. My thesis is supported and described on the basis of a physicist's model which studies the droplets behavior when emitted by the respiratory apparatus of an infected person, symptomatic or not. The intermediate dimensioned droplets are proved to be changed into aerosol, losing their water content and becoming seriously contagious, but in their initial phase they could be easily caught by a simple surgical mask. The actual efficiency of FFP3 masks has been examined and found to be lower than expected.


id: cord-324444-t697xw4y
author: Rodriguez-Palacios, Alexander
date: 2020-04-10
txt: ./txt/cord-324444-t697xw4y.txt
cache: ./cache/cord-324444-t697xw4y.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1101/2020.04.07.20045617
doi: 10.1101/2020.04.07.20045617
summary:
  However, given that asymptomatic individuals, not wearing masks within the public, can be highly contagious for COVID-19, prevention of environmental droplet contamination (EnDC) from coughing/sneezing/speech is fundamental to reducing transmission. When used as double-layers, textiles were as effective as medical mask/surgical-cloth materials, reducing droplet dispersion to <10cm, and the area of circumferential contamination to ~0.3%. The synchronized implementation of EDBs as a community droplet reduction solution (i.e., face covers/scarfs/masks & surface covers) could reduce EnDC and the risk of transmitting or acquiring infectious respiratory pathogens, including COVID-19. defibrinated sheep blood, placed on a need droplets to facilitate their expulsion, transmission and EnDC 12 , we first validated a rapid 116 spray-simulation model of droplets (mimicking a sneeze) using a bacterial-suspension to quantify 117 the extent by which widely-available household textiles reduced the ejection/long-distance flight of 118 .

title:
  Textile Masks and Surface Covers - A ''Universal Droplet Reduction Model'' Against Respiratory Pandemics

abstract:
  The main form of COVID-19 transmission is via oral-respiratory droplet contamination (droplet; very small drop of liquid) produced when individuals talk, sneeze or cough. In hospitals, health-care workers wear facemasks as a minimum medical droplet precaution to protect themselves. Due to the shortage of masks during the pandemic, priority is given to hospitals for their distribution. As a result, the availability/use of medical masks is discouraged for the public. However, given that asymptomatic individuals, not wearing masks within the public, can be highly contagious for COVID-19, prevention of environmental droplet contamination (EnDC) from coughing/sneezing/speech is fundamental to reducing transmission. As an immediate solution to promote public droplet safety, we assessed household textiles to quantify their potential as effective environmental droplet barriers (EDBs). The synchronized implementation of a universal community droplet reduction solution is discussed as a model against COVID-19. Using a bacterial-suspension spray simulation model of droplet ejection (mimicking a sneeze), we quantified the extent by which widely available clothing fabrics reduce the dispersion of droplets onto surfaces within 1.8m, the minimum distance recommended for COVID-19 social distancing. All textiles reduced the number of droplets reaching surfaces, restricting their dispersion to <30cm, when used as single layers. When used as double-layers, textiles were as effective as medical mask/surgical-cloth materials, reducing droplet dispersion to <10cm, and the area of circumferential contamination to ~0.3%. The synchronized implementation of EDBs as a community droplet reduction solution (i.e., face covers/scarfs/masks & surface covers) could reduce EnDC and the risk of transmitting or acquiring infectious respiratory pathogens, including COVID-19.


id: cord-325205-8yug5jjx
title: On coughing and airborne droplet transmission to humans
author: Dbouk, Talib
date: 2020-05-01
txt: ./txt/cord-325205-8yug5jjx.txt
cache: ./cache/cord-325205-8yug5jjx.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32574229/
doi: 10.1063/5.0011960
summary:
  This paper employs computational multiphase fluid dynamics and heat transfer to investigate transport, dispersion, and evaporation of saliva particles arising from a human cough. For a mild human cough in air at 20 °C and 50% relative humidity, we found that human saliva-disease-carrier droplets may travel up to unexpected considerable distances depending on the wind speed. 4. The numerical modeling approach to capture the complex varying space and time scales, e.g., both heat and mass transfer considerations, modeling of mass and phase changes due to droplet evaporation, coalescence, breakup, and turbulent dispersion in interaction with the bulk flow field. A human cough: saliva droplet''s disease-carrier particles cannot travel more than 2 m in space at approximately zero wind speed. This study shows that, when a person coughs, the wind speed in an open space environment significantly influences the distance that airborne disease-carrier droplets travel.

abstract:
  Our understanding of the mechanisms of airborne transmission of viruses is incomplete. This paper employs computational multiphase fluid dynamics and heat transfer to investigate transport, dispersion, and evaporation of saliva particles arising from a human cough. An ejection process of saliva droplets in air was applied to mimic the real event of a human cough. We employ an advanced three-dimensional model based on fully coupled Eulerian–Lagrangian techniques that take into account the relative humidity, turbulent dispersion forces, droplet phase-change, evaporation, and breakup in addition to the droplet–droplet and droplet–air interactions. We computationally investigate the effect of wind speed on social distancing. For a mild human cough in air at 20 °C and 50% relative humidity, we found that human saliva-disease-carrier droplets may travel up to unexpected considerable distances depending on the wind speed. When the wind speed was approximately zero, the saliva droplets did not travel 2 m, which is within the social distancing recommendations. However, at wind speeds varying from 4 km/h to 15 km/h, we found that the saliva droplets can travel up to 6 m with a decrease in the concentration and liquid droplet size in the wind direction. Our findings imply that considering the environmental conditions, the 2 m social distance may not be sufficient. Further research is required to quantify the influence of parameters such as the environment’s relative humidity and temperature among others.


id: cord-334166-vll4s0xq
title: Reducing Aerosolised Particles and Droplet Spread in Endoscopic Sinus Surgery during COVID‐19
author: Jones, Huw AS
date: 2020-08-15
txt: ./txt/cord-334166-vll4s0xq.txt
cache: ./cache/cord-334166-vll4s0xq.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/32798323/
doi: 10.1002/lary.29065
summary:
  RESULTS: The use of a negative pressure mask technique resulted in a 98% reduction in the fine particulate aerosol simulation, and eliminated larger respiratory droplet spread during simulated ESS, including during external drill activation. CONCLUSIONS: As global ENT services resume routine elective operating, we demonstrate the potential use of a simple negative pressure mask technique to reduce the risk of viral exposure for the operator and theatre staff during ESS. A few studies have sought to investigate this concern in a simulated setting and have demonstrated significant droplet spread during endoscopic sinus surgery, particularly when using powered drills 15, 16 . This proof of concept study demonstrates that a negative pressure mask can effectively reduce both fine droplet nuclei aerosol and larger droplet spread during endoscopic sinus surgery using powered instruments. This study demonstrates the effectiveness of a simple negative pressure mask in reducing droplets and respiratory nuclei generated during endoscopic sinus surgery, thus reducing potential exposure for both operator and theatre staff.

abstract:
  OBJECTIVES: The presence of high SARS‐Cov‐2 viral loads in the upper airway, including the potential for aerosolised transmission of viral particles, has generated significant concern amongst Otolaryngologists worldwide, particularly those performing Endoscopic Sinus Surgery (ESS). We evaluated a simple negative pressure mask technique to reduce viral exposure. METHODS: Two models simulating respiratory droplets >5‐10 μm and fine respiratory nuclei <5 μm using fluorescein dye and wood smoke respectively were utilised in a fixed cadaveric study in a controlled environment. Using Ultra‐Violet light, fluorescein droplet spread was assessed during simulated ESS with powered microdebrider and powered drilling. Wood smoke ejection was used to evaluate fine particulate escape from a negative pressure mask using digital subtraction image processing. RESULTS: The use of a negative pressure mask technique resulted in a 98% reduction in the fine particulate aerosol simulation, and eliminated larger respiratory droplet spread during simulated ESS, including during external drill activation. CONCLUSIONS: As global ENT services resume routine elective operating, we demonstrate the potential use of a simple negative pressure mask technique to reduce the risk of viral exposure for the operator and theatre staff during ESS.


id: cord-335874-mtfe9uq1
author: Chao, C.Y.H.
date: 2008-11-07
url: https://www.sciencedirect.com/science/article/pii/S0021850208001882
doi: 10.1016/j.jaerosci.2008.10.003
title:
  Characterization of expiration air jets and droplet size distributions immediately at the mouth opening

abstract:
  Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The average expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the experimental setting, evaporation and condensation effects had negligible impact on the measured droplet size. The geometric mean diameter of droplets from coughing was 13.5 μm and it was 16.0 μm for speaking (counting 1–100). The estimated total number of droplets expelled ranged from 947 to 2085 per cough and 112–6720 for speaking. The estimated droplet concentrations for coughing ranged from 2.4 to 5.2 cm(−3) per cough and 0.004–0.223 cm(−3) for speaking.


id: cord-353170-fiadxpar
author: George, Ajith
date: 2020-05-31
txt: ./txt/cord-353170-fiadxpar.txt
cache: ./cache/cord-353170-fiadxpar.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1111/coa.13591
doi: 10.1111/coa.13591
summary:
  Common sense would dictate this instinctively reduces the dispersion of aerosol and droplets and thus the spread of contact and airborne infections. Common sense would dictate this instinctively reduces the dispersion of aerosol and droplets and thus the spread of contact and airborne infections. On impact with smooth surfaces droplets disperse to smaller sizes and can aerosolise. One suggestion is the use of facemasks to help reduce the risk of inadvertent droplet dispersion (2) .  Droplets produced by coughing or sneezing carry a higher viral particle load and can be reduced by wearing a surgical mask in turn helping reducing infection transmission  The SNAP device is an effective and safe method of providing access to the nasal cavity during nasoendoscopy whilst also providing a barrier of a surgical mask to protect against droplet dispersion  Reducing the exposure to pathogens for all healthcare works facilitates a return of

title:
  Correspondence‐Technical Note: Safe Nasoendoscopy Assisted Procedure in the Post COVID‐19 Pandemic Era

abstract:
  For centuries it has been humankind's instinct to cover the mouth and nose when coughing or sneezing. Common sense would dictate this instinctively reduces the dispersion of aerosol and droplets and thus the spread of contact and airborne infections.


id: cord-356118-7yuzl5he
title: Method for contamination of filtering facepiece respirators by deposition of MS2 viral aerosols
author: Woo, Myung-Heui
date: 2010-10-31
url: https://www.ncbi.nlm.nih.gov/pubmed/32226122/
doi: 10.1016/j.jaerosci.2010.07.003
abstract:
  Abstract A droplet/aerosol loading chamber was designed to deliver uniform droplets/aerosols onto substrates. An ultrasonic nebulizer was used to produce virus-containing droplets from artificial saliva to emulate those from coughing and sneezing. The operating conditions were determined by adjusting various parameters to achieve loading density and uniformity requirements. The count median diameter and mass median diameter were 0.5–2 and 3–4μm, respectively, around the loading location when 35% relative humidity was applied. The average loading density was ∼2×103 plaque-forming units/cm2 for 5-min loading time with a virus titer of 107 plaque-forming units/mL. Six different filtering facepiece respirators from commercial sources were loaded to evaluate uniform distribution. For each of the six FFRs, the virus loading uniformity within a sample and across numerous samples was 19.21% and 12.20%, respectively. This system supports a standard method for loading viable bioaerosols onto specimen surfaces when different decontamination techniques are to be compared.


