An upper bound on one-to-one exposure to infectious human respiratory particles

There is ample evidence that masking and social distancing are effective in reducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. However, due to the complexity of airborne disease transmission, it is difficult to quantify their effectiveness, especially in the case of one-to-one exposure. Here, we introduce the concept of an upper bound for one-to-one exposure to infectious human respiratory particles and apply it to SARS-CoV-2. To calculate exposure and infection risk, we use a comprehensive database on respiratory particle size distribution; exhalation flow physics; leakage from face masks of various types and fits measured on human subjects; consideration of ambient particle shrinkage due to evaporation; and rehydration, inhalability, and deposition in the susceptible airways. We find, for a typical SARS-CoV-2 viral load and infectious dose, that social distancing alone, even at 3.0 m between two speaking individuals, leads to an upper bound of 90% for risk of infection after a few minutes. If only the susceptible wears a face mask with infectious speaking at a distance of 1.5 m, the upper bound drops very significantly; that is, with a surgical mask, the upper bound reaches 90% after 30 min, and, with an FFP2 mask, it remains at about 20% even after 1 h. When both wear a surgical mask, while the infectious is speaking, the very conservative upper bound remains below 30% after 1 h, but, when both wear a well-fitting FFP2 mask, it is 0.4%. We conclude that wearing appropriate masks in the community provides excellent protection for others and oneself, and makes social distancing less important.

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Aerosol transport measurements and assessment of risk from infectious aerosols: a case study of two German cash-and-carry hardware/DIY stores

10.1101/2021.05.21.21257577 ◽

2021 ◽

Author(s):

eberhard Bodenschatz ◽

Gholamhossein Bagheri ◽

Bardia Hejazi ◽

Birte Thiede ◽

Oliver Schlenczek

Keyword(s):

Upper Bound ◽

Disease Transmission ◽

Face Mask ◽

Indoor Environments ◽

Aerosol Dynamics ◽

Direct Exposure ◽

Decay Times ◽

Dominant Feature ◽

Aerosol Dispersion ◽

Cash And Carry

We report experimental results on aerosol dispersion in two large German cash-and-carry hardware/DIY stores to better understand the factors contributing to disease transmission by infectious human aerosols in large indoor environments. We examined the transport of aerosols similar in size to human respiratory aerosols (0.3μm-10μm) in representative locations, such as high-traffic areas and restrooms. In restrooms, the observed decay of aerosol concentrations was consistent with well-mixed air exchange. In all other locations, fast decay times were measured, which were found to be independent of aerosol size (typically a few minutes). From this, we conclude that in the main retail areas, including at checkouts, rapid turbulent mixing and advection is the dominant feature in aerosol dynamics. With this, the upper bound of risk for airborne disease transmission to a susceptible is determined by direct exposure to the exhalation cloud of an infectious. For the example of the SARS-CoV-2 virus, we find when speaking without a face mask and aerosol sizes up to an exhalation (wet) diameter of 50μm, a distance of 1.5me to be unsafe. However, at the smallest distance between an infectious and a susceptible, while wearing typical surgical masks and for all sizes of exhaled aerosol, the upper bound of infection risk is only ∼ 5% and decreases further by a factor of 100 (∼ 0.05%) for typical FFP2 masks for a duration of 20 min. This upper bound is very conservative and we expect the actual risk for typical encounters to be much lower. The risks found here are comparable to what might be expected in calm outdoor weather.

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Beyond Six Feet: A Guideline to Limit Indoor Airborne Transmission of COVID-19

10.1101/2020.08.26.20182824 ◽

2020 ◽

Cited By ~ 5

Author(s):

Martin Z. Bazant ◽

John W. M. Bush

Keyword(s):

Disease Transmission ◽

Face Mask ◽

Contact Tracing ◽

Cumulative Exposure ◽

Air Filtration ◽

Airborne Transmission ◽

Infectious Dose ◽

Indoor Space ◽

Order Of Magnitude ◽

Enclosed Space

The current revival of the world’s economy is being predicated on social distancing, specifically the Six-Foot Rule, a guideline that offers little protection from pathogen-bearing aerosol droplets sufficiently small to be continuously mixed through an indoor space. The importance of airborne transmission of COVID-19 is now widely recognized. While tools for risk assessment have recently been developed, no safety guideline has been proposed to protect against it. We here build upon models of airborne disease transmission in order to derive an indoor safety guideline that would impose an upper bound on the “cumulative exposure time”, the product of the number of occupants and their time in an enclosed space. We demonstrate how this bound depends on the rates of ventilation and air filtration, dimensions of the room, breathing rate, respiratory activity and face-mask use of its occupants, and infectiousness of the respiratory aerosols. By synthesizing available data from the best characterized indoor spreading events with respiratory drop-size distributions, we estimate an infectious dose on the order of ten aerosol-borne virions. The new virus is thus inferred to be an order of magnitude more infectious than its forerunner, (SARS-CoV), consistent with the pandemic status achieved by COVID-19. Case studies are presented for classrooms and nursing homes, and a spreadsheet and online app are provided to facilitate use of our guideline. Implications for contact tracing and quarantining are considered, appropriate caveats enumerated. Particular consideration is given to respiratory jets, that may substantially elevate risk when face masks are not worn.

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A guideline to limit indoor airborne transmission of COVID-19

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2018995118 ◽

2021 ◽

Vol 118 (17) ◽

pp. e2018995118

Author(s):

Martin Z. Bazant ◽

John W. M. Bush

Keyword(s):

Disease Transmission ◽

Face Mask ◽

Contact Tracing ◽

Cumulative Exposure ◽

Air Filtration ◽

Airborne Transmission ◽

Infectious Dose ◽

Indoor Space ◽

Order Of Magnitude ◽

Enclosed Space

The current revival of the American economy is being predicated on social distancing, specifically the Six-Foot Rule, a guideline that offers little protection from pathogen-bearing aerosol droplets sufficiently small to be continuously mixed through an indoor space. The importance of airborne transmission of COVID-19 is now widely recognized. While tools for risk assessment have recently been developed, no safety guideline has been proposed to protect against it. We here build on models of airborne disease transmission in order to derive an indoor safety guideline that would impose an upper bound on the “cumulative exposure time,” the product of the number of occupants and their time in an enclosed space. We demonstrate how this bound depends on the rates of ventilation and air filtration, dimensions of the room, breathing rate, respiratory activity and face mask use of its occupants, and infectiousness of the respiratory aerosols. By synthesizing available data from the best-characterized indoor spreading events with respiratory drop size distributions, we estimate an infectious dose on the order of 10 aerosol-borne virions. The new virus (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]) is thus inferred to be an order of magnitude more infectious than its forerunner (SARS-CoV), consistent with the pandemic status achieved by COVID-19. Case studies are presented for classrooms and nursing homes, and a spreadsheet and online app are provided to facilitate use of our guideline. Implications for contact tracing and quarantining are considered, and appropriate caveats enumerated. Particular consideration is given to respiratory jets, which may substantially elevate risk when face masks are not worn.

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COVID-19 Monitoring System using Social Distancing and Face Mask Detection on Surveillance video datasets

2021 International Conference on Emerging Smart Computing and Informatics (ESCI) ◽

10.1109/esci50559.2021.9396783 ◽

2021 ◽

Author(s):

Sahana Srinivasan ◽

R Rujula Singh ◽

Ruchita R Biradar ◽

SA Revathi

Keyword(s):

Monitoring System ◽

Face Mask ◽

Surveillance Video ◽

Social Distancing

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Splatters and Aerosols Contamination in Dental Aerosol Generating Procedures

Applied Sciences ◽

10.3390/app11041914 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1914

Author(s):

Pingping Han ◽

Honghui Li ◽

Laurence J. Walsh ◽

Sašo Ivanovski

Keyword(s):

Particle Size ◽

Disease Transmission ◽

High Speed ◽

Low Speed ◽

Dental Procedures ◽

Dental Equipment ◽

Produce Contamination ◽

Fluorescein Dye ◽

Filter Papers ◽

Airborne Disease

Dental aerosol-generating procedures produce a large amount of splatters and aerosols that create a major concern for airborne disease transmission, such as COVID-19. This study established a method to visualise splatter and aerosol contamination by common dental instrumentation, namely ultrasonic scaling, air-water spray, high-speed and low-speed handpieces. Mock dental procedures were performed on a mannequin model, containing teeth in a typodont and a phantom head, using irrigation water containing fluorescein dye as a tracer. Filter papers were placed in 10 different locations to collect splatters and aerosols, at distances ranging from 20 to 120 cm from the source. All four types of dental equipment produced contamination from splatters and aerosols. At 120 cm away from the source, the high-speed handpiece generated the greatest amount and size (656 ± 551 μm) of splatter particles, while the triplex syringe generated the largest amount of aerosols (particle size: 1.73 ± 2.23 μm). Of note, the low-speed handpiece produced the least amount and size (260 ± 142 μm) of splatter particles and the least amount of aerosols (particle size: 4.47 ± 5.92 μm) at 120 cm. All four dental AGPs produce contamination from droplets and aerosols, with different patterns of distribution. This simple model provides a method to test various preventive strategies to reduce risks from splatter and aerosols.

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Addressing the COVID-19 transmission in inner Brazil by a mathematical model

Scientific Reports ◽

10.1038/s41598-021-90118-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

G. B. Almeida ◽

T. N. Vilches ◽

C. P. Ferreira ◽

C. M. C. B. Fortaleza

Keyword(s):

Mathematical Model ◽

Disease Transmission ◽

Abiotic Factors ◽

Severe Pneumonia ◽

Mitigation Strategies ◽

Social Distancing ◽

Control Disease ◽

Set Up ◽

Novel Coronavirus ◽

Public Health Strategies

AbstractIn 2020, the world experienced its very first pandemic of the globalized era. A novel coronavirus, SARS-CoV-2, is the causative agent of severe pneumonia and has rapidly spread through many nations, crashing health systems and leading a large number of people to death. In Brazil, the emergence of local epidemics in major metropolitan areas has always been a concern. In a vast and heterogeneous country, with regional disparities and climate diversity, several factors can modulate the dynamics of COVID-19. What should be the scenario for inner Brazil, and what can we do to control infection transmission in each of these locations? Here, a mathematical model is proposed to simulate disease transmission among individuals in several scenarios, differing by abiotic factors, social-economic factors, and effectiveness of mitigation strategies. The disease control relies on keeping all individuals’ social distancing and detecting, followed by isolating, infected ones. The model reinforces social distancing as the most efficient method to control disease transmission. Moreover, it also shows that improving the detection and isolation of infected individuals can loosen this mitigation strategy. Finally, the effectiveness of control may be different across the country, and understanding it can help set up public health strategies.

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The effect of social distancing on the reach of an epidemic in social networks

Journal of Economic Interaction and Coordination ◽

10.1007/s11403-021-00322-9 ◽

2021 ◽

Author(s):

Gregory Gutin ◽

Tomohiro Hirano ◽

Sung-Ha Hwang ◽

Philip R. Neary ◽

Alexis Akira Toda

Keyword(s):

Public Health ◽

Infectious Disease ◽

Social Networks ◽

Monte Carlo Simulation ◽

Monte Carlo ◽

Disease Transmission ◽

Global Level ◽

Social Distancing ◽

The Public ◽

Simulation Results

AbstractHow does social distancing affect the reach of an epidemic in social networks? We present Monte Carlo simulation results of a susceptible–infected–removed with social distancing model. The key feature of the model is that individuals are limited in the number of acquaintances that they can interact with, thereby constraining disease transmission to an infectious subnetwork of the original social network. While increased social distancing typically reduces the spread of an infectious disease, the magnitude varies greatly depending on the topology of the network, indicating the need for policies that are network dependent. Our results also reveal the importance of coordinating policies at the ‘global’ level. In particular, the public health benefits from social distancing to a group (e.g. a country) may be completely undone if that group maintains connections with outside groups that are not following suit.

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Examining the interplay between face mask usage, asymptomatic transmission, and social distancing on the spread of COVID-19

Scientific Reports ◽

10.1038/s41598-021-94960-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Adam Catching ◽

Sara Capponi ◽

Ming Te Yeh ◽

Simone Bianco ◽

Raul Andino

Keyword(s):

Social Distance ◽

Large Fraction ◽

Real Life ◽

Virus Transmission ◽

Face Mask ◽

Social Distancing ◽

Viral Spread ◽

The Face ◽

Asymptomatic Individuals ◽

High Virus

AbstractCOVID-19’s high virus transmission rates have caused a pandemic that is exacerbated by the high rates of asymptomatic and presymptomatic infections. These factors suggest that face masks and social distance could be paramount in containing the pandemic. We examined the efficacy of each measure and the combination of both measures using an agent-based model within a closed space that approximated real-life interactions. By explicitly considering different fractions of asymptomatic individuals, as well as a realistic hypothesis of face masks protection during inhaling and exhaling, our simulations demonstrate that a synergistic use of face masks and social distancing is the most effective intervention to curb the infection spread. To control the pandemic, our models suggest that high adherence to social distance is necessary to curb the spread of the disease, and that wearing face masks provides optimal protection even if only a small portion of the population comply with social distance. Finally, the face mask effectiveness in curbing the viral spread is not reduced if a large fraction of population is asymptomatic. Our findings have important implications for policies that dictate the reopening of social gatherings.

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COVID-19 Pandemic Response Simulation in a Large City: Impact of Nonpharmaceutical Interventions on Reopening Society

Medical Decision Making ◽

10.1177/0272989x211003081 ◽

2021 ◽

pp. 0272989X2110030

Author(s):

Serin Lee ◽

Zelda B. Zabinsky ◽

Judith N. Wasserheit ◽

Stephen M. Kofsky ◽

Shan Liu

Keyword(s):

Large City ◽

Face Mask ◽

School Closure ◽

Contact Tracing ◽

The Novel ◽

Agent Based ◽

Social Distancing ◽

Variable Compliance ◽

Novel Coronavirus ◽

Nonpharmaceutical Interventions

As the novel coronavirus (COVID-19) pandemic continues to expand, policymakers are striving to balance the combinations of nonpharmaceutical interventions (NPIs) to keep people safe and minimize social disruptions. We developed and calibrated an agent-based simulation to model COVID-19 outbreaks in the greater Seattle area. The model simulated NPIs, including social distancing, face mask use, school closure, testing, and contact tracing with variable compliance and effectiveness to identify optimal NPI combinations that can control the spread of the virus in a large urban area. Results highlight the importance of at least 75% face mask use to relax social distancing and school closure measures while keeping infections low. It is important to relax NPIs cautiously during vaccine rollout in 2021.

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