scholarly journals Assessment of Airborne Disease Transmission Risk and Energy Impact of HVAC Mitigation Strategies

2021 ◽  
Author(s):  
Michael J. Risbeck ◽  
Martin Z. Bazant ◽  
Zhanhong Jiang ◽  
Young M. Lee ◽  
Kirk H. Drees ◽  
...  
Keyword(s):  
Disease Transmission ◽  
Significant Risk ◽  
Mitigation Strategies ◽  
Transmission Risk ◽  
Disease Spread ◽  
Particle Removal ◽  
Outdoor Air ◽  
Common Basis ◽  
Air Ventilation ◽  
Airborne Disease

The COVID-19 pandemic has focused renewed attention on the ways in which building HVAC systems may be operated to mitigate the risk of airborne disease transmission. The most common suggestion is to increase outdoor-air ventilation rates so as to dilute the concentrations of infectious aerosol particles indoors. Although this strategy does reduce the likelihood of disease spread, it is often much more costly than other strategies that provide equivalent particle removal or deactivation. To address this tradeoff and arrive at practical recommendations, we explain how different mitigation strategies can be expressed in terms of equivalent outdoor air (EOA) to provide a common basis for energy analysis. We then show the effects of each strategy on EOA delivery and energy cost in simulations of realistic buildings in a variety of climates. Key findings are that in-duct filtration is often the most efficient mitigation strategy, while significant risk reduction generally requires increasing total airflow to the system, either through adjusted HVAC setpoints or standalone disinfection devices.

scholarly journals A Computational Framework for Transmission Risk Assessment of Aerosolized Particles in Classrooms

2021 ◽  
Author(s):  
Kendrick Tan ◽  
Boshun Gao ◽  
Cheng-Hau Yang ◽  
Emily Johnson ◽  
Ming-Chen Hsu ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Disease Transmission ◽  
Ventilation Rate ◽  
Mitigation Strategies ◽  
Transmission Risk ◽  
Computational Framework ◽  
Seating Arrangement ◽  
K 12 ◽  
Education Administrators ◽  
Airborne Disease

Abstract The ongoing COVID-19 pandemic has rendered confined spaces as high-risk areas. There is an increasing push to resume in-person activities, for instance, teaching in K-12 and university settings. It becomes important to evaluate the risk of airborne disease transmission while accounting for the physical presence of humans, furniture, and electronic equipment, as well as ventilation. Here, we present a computational framework based on detailed flow physics simulations that allows straightforward evaluation of various seating and operating scenarios to identify risk factors and assess the effectiveness of various mitigation strategies. These scenarios include seating arrangement changes, presence/absence of computer screens, ventilation rate changes, and presence/absence of mask-wearing. This approach democratizes risk assessment by automating a key bottleneck in simulation-based analysis--creating an adequately refined mesh around multiple complex geometries. Not surprisingly, we find that wearing masks (with at least 74% inward protection efficiency) significantly reduced transmission risk against unmasked and infected individuals. The availability of such an analysis approach will allow education administrators, government officials (courthouses, police stations), and hospital administrators to make informed decisions on seating arrangements and operating procedures.

scholarly journals Modeling and Multiobjective Optimization of Indoor Airborne Disease Transmission Risk and Associated Energy Consumption for Building HVAC Systems

2021 ◽  
Author(s):  
Michael James Risbeck ◽  
Martin Z. Bazant ◽  
Zhanhong Jiang ◽  
Young M Lee ◽  
Kirk H Drees ◽  
...  
Keyword(s):  
Energy Consumption ◽  
Disease Transmission ◽  
Weather Conditions ◽  
Infection Risk ◽  
Hvac Systems ◽  
Transmission Risk ◽  
Disease Spread ◽  
Risk Levels ◽  
Occupant Comfort ◽  
Airborne Disease

The COVID-19 pandemic has renewed interest in assessing how the operation of HVAC systems influences the risk of airborne disease transmission in buildings. Various processes, such as ventilation and filtration, have been shown to reduce the probability of disease spread by removing or deactivating exhaled aerosols that potentially contain infectious material. However, such qualitative recommendations fail to specify how much of these or other disinfection techniques are needed to achieve acceptable risk levels in a particular space. An additional complication is that application of these techniques inevitably increases energy costs, the magnitude of which can vary significantly based on local weather. Moreover, the operational flexibility available to the HVAC system may be inherently limited by equipment capacities and occupant comfort requirements. Given this knowledge gap, we propose a set of dynamical models that can be used to estimate airborne transmission risk and energy consumption for building HVAC systems, based on comfort preferences and weather conditions. By combining physics-based material balances with phenomenological models of the HVAC control system, it is possible to predict time-varying airflows and other HVAC variables, which are then used to calculate the key metrics. Through a variety of examples involving real and simulated commercial buildings, we show that our models can be used for monitoring purposes by applying them directly to transient building data as operated, or they may be embedded within a multi-objective optimization framework to evaluate the tradeoff between infection risk and energy consumption. By combining these applications, building managers can determine which spaces are in need of infection risk reduction and how to provide that reduction at the lowest energy cost. The key finding is that both the baseline infection risk and the most energy-efficient disinfection source can vary significantly from space to space and depend sensitively on the weather, thus underscoring the importance of the quantitative predictions provided by the models.

scholarly journals Livestock movement informs the risk of disease spread in traditional production systems in East Africa

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Divine Ekwem ◽  
Thomas A. Morrison ◽  
Richard Reeve ◽  
Jessica Enright ◽  
Joram Buza ◽  
...  
Keyword(s):  
Disease Transmission ◽  
Production Systems ◽  
Control Strategies ◽  
Herd Size ◽  
Transmission Risk ◽  
Disease Spread ◽  
Transmission Potential ◽  
Spatial And Temporal Scales ◽  
Transmission Distance ◽  
Risk Of Disease

AbstractIn Africa, livestock are important to local and national economies, but their productivity is constrained by infectious diseases. Comprehensive information on livestock movements and contacts is required to devise appropriate disease control strategies; yet, understanding contact risk in systems where herds mix extensively, and where different pathogens can be transmitted at different spatial and temporal scales, remains a major challenge. We deployed Global Positioning System collars on cattle in 52 herds in a traditional agropastoral system in western Serengeti, Tanzania, to understand fine-scale movements and between-herd contacts, and to identify locations of greatest interaction between herds. We examined contact across spatiotemporal scales relevant to different disease transmission scenarios. Daily cattle movements increased with herd size and rainfall. Generally, contact between herds was greatest away from households, during periods with low rainfall and in locations close to dipping points. We demonstrate how movements and contacts affect the risk of disease spread. For example, transmission risk is relatively sensitive to the survival time of different pathogens in the environment, and less sensitive to transmission distance, at least over the range of the spatiotemporal definitions of contacts that we explored. We identify times and locations of greatest disease transmission potential and that could be targeted through tailored control strategies.

Mapping the Potential for Infectious Disease Transmission in a Wide-Body Aircraft Cabin

2019 ◽  
Author(s):  
Seif Mahmoud ◽  
James S. Bennett ◽  
Mohammad H. Hosni ◽  
Byron Jones
Keyword(s):  
Infectious Diseases ◽  
Disease Transmission ◽  
Radial Distance ◽  
Transmission Risk ◽  
Disease Spread ◽  
Health Concern ◽  
Tracer Gas ◽  
Infectious Disease Transmission ◽  
Gas Concentration ◽  
Aircraft Cabin

Abstract With more than two billion passengers annually, in-flight transmission of infectious diseases is a major global health concern. It is widely believed that principal transmission risk associated with air travel for most respiratory infectious diseases is limited to within two rows of an infectious passenger. However, several passengers became infected despite sitting several rows away from the contagious passenger. This work thoroughly investigated the potential for disease spread inside airplane cabins using tracer gas to quantify airborne dispersion. Measurements were conducted in a full-scale, 11-row mock-up of a wide-body aircraft cabin. Heated mannequins to simulate passengers’ thermal load were placed on the cabin seats. Tracer gas was injected at the breathing level at four different hypothetical contagious passenger locations. The tracer gas concentration was measured radially up to 3.35 m away from the injection location representing four rows of a standard aircraft. A four-port sampling tree was used to collect samples at the breathing level at four different radial locations simultaneously. Each port was sampled for 30 minutes. A total of 42 tests were conducted in matching pairs to alleviate potential statistical or measurements bias. The results showed that the airflow pattern inside the mock-up airplane cabin plays a major role in determining tracer gas concentration meaning that the concentration at the same radial distance in different directions are not necessarily the same. Also, due to the air distribution pattern and cabin walls, concentrations at some seats may be higher than the source seat.

scholarly journals Are Historical Buildings More Adaptive to Minimize the Risks of Airborne Transmission of Viruses and Public Health? A Study of the Hazzazi House in Jeddah (Saudi Arabia)

2021 ◽  
Vol 18 (7) ◽  
pp. 3601
Author(s):  
Alaa Alaidroos ◽  
Ayad Almaimani ◽  
Ahmed Baik ◽  
Mohamed Al-Amodi ◽  
Khan Rubayet Rahaman
Keyword(s):  
Saudi Arabia ◽  
Built Environment ◽  
Disease Transmission ◽  
Natural Ventilation ◽  
Historical Building ◽  
Heritage Buildings ◽  
Spatial Configurations ◽  
Air Ventilation ◽  
Heritage Building ◽  
Airborne Disease

The coronavirus (COVID-19) pandemic has brought immense challenges to the natural and built environment to develop an antivirus-enabled model for reducing potential risks of spreading the virus at varied scales such as buildings, neighborhoods, and cities. Spatial configurations of structures may hinder or assist the spread of viruses in the built environment. In this study, we have hypothesized that suitable air ventilation in historic buildings may enhance the built environment to combat the spreading of infectious viruses. To provide such quantitative shreds of evidence, we have generated and estimated an integrated model to summarize obtained information by considering natural ventilation, wind speed, inflow and outflow, wind direction, and forecasting the associated risks of airborne disease transmission in a historical building (i.e., the Hazzazi House in particular). Intrinsically, the results have demonstrated that the effectiveness of natural ventilation has directly influenced reducing the risks of transmitting airborne infectious viruses for the selected heritage building in Jeddah (Saudi Arabia). The adopted methods in this research may be useful to understand the potentials of conserving old heritage buildings. Consequently, the results demonstrate that natural air ventilation systems are critical to combat the spread of infectious diseases in the pandemic.

scholarly journals Multi-Scale Airborne Infectious Disease Transmission

2020 ◽  
Author(s):  
Charles F. Dillon ◽  
Michael B. Dillon
Keyword(s):  
Disease Transmission ◽  
Fungal Pathogens ◽  
Field Experiments ◽  
Disease Outbreak ◽  
Disease Spread ◽  
Epidemic Disease ◽  
Airborne Transmission ◽  
Regulatory Standards ◽  
Airborne Disease ◽  
Methodological Guidelines

Airborne disease transmission is central to many scientific disciplines including agriculture, veterinary biosafety, medicine, and public health. Legal and regulatory standards are in place to prevent agricultural, nosocomial, and community airborne disease transmission. However, the overall importance of the airborne pathway is underappreciated, e.g.,, US National Library of Medicine’s Medical Subjects Headings (MESH) thesaurus lacks an airborne disease transmission indexing term. This has practical consequences as airborne precautions to control epidemic disease spread may not be taken when airborne transmission is important, but unrecognized. Publishing clearer practical methodological guidelines for surveillance studies and disease outbreak evaluations could help address this situation. To inform future work, this paper highlights selected, well-established airborne transmission events - largely cases replicated in multiple, independently conducted scientific studies. Methodologies include field experiments, modeling, epidemiology studies, disease outbreak investigations and mitigation studies. Collectively, this literature demonstrates that airborne viruses, bacteria, and fungal pathogens have the capability to cause disease in plants, animals, and humans over multiple distances – from near range (< 5 m) to continental (> 500 km) in scale. The plausibility and implications of undetected airborne disease transmission are discussed, including the notable underreporting of disease burden for several airborne transmitted diseases.

scholarly journals Airflows inside passenger cars and implications for airborne disease transmission

2020 ◽  
Vol 7 (1) ◽  
pp. eabe0166 ◽  
Author(s):  
Varghese Mathai ◽  
Asimanshu Das ◽  
Jeffrey A. Bailey ◽  
Kenneth Breuer
Keyword(s):  
Disease Transmission ◽  
Respiratory Diseases ◽  
Passive Scalar ◽  
Elevated Risk ◽  
Pathogen Transmission ◽  
Transmission Risk ◽  
Residence Times ◽  
Passenger Cars ◽  
Complex Fluid ◽  
Airborne Disease

Transmission of highly infectious respiratory diseases, including SARS-CoV-2, is facilitated by the transport of exhaled droplets and aerosols that can remain suspended in air for extended periods of time. A passenger car cabin represents one such situation with an elevated risk of pathogen transmission. Here, we present results from numerical simulations to assess how the in-cabin microclimate of a car can potentially spread pathogenic species between occupants for a variety of open and closed window configurations. We estimate relative concentrations and residence times of a noninteracting, passive scalar—a proxy for infectious particles—being advected and diffused by turbulent airflows inside the cabin. An airflow pattern that travels across the cabin, farthest from the occupants, can potentially reduce the transmission risk. Our findings reveal the complex fluid dynamics during everyday commutes and nonintuitive ways in which open windows can either increase or suppress airborne transmission.

scholarly journals Particle Based Model for Airborne Disease Transmission

2020 ◽  
Author(s):  
Michael B Dillon ◽  
Charles F Dillon
Keyword(s):  
Single Particle ◽  
Disease Transmission ◽  
A Priori ◽  
Region Of Interest ◽  
Infectious Agent ◽  
Geographic Region ◽  
Disease Spread ◽  
List Type ◽  
Executive Summary ◽  
Airborne Disease

Executive SummaryPrior literature documents cases of airborne infectious disease transmission at distances ranging from ≥ 2 m to inter-continental in scale. Physics- and biology- based models describe the key aspects of these airborne disease transmission events, but important gaps remain. This report extends current approaches by developing a new, single-particle based theory that (a) assesses the likelihood of rare airborne infections (where individuals inhale either one or no infectious particles) and (b) explicitly accounts for the variability in airborne exposures and population susceptibilities within a geographic region of interest. For these hazards, airborne particle fate and transport is independent of particulate concentration, and so results for complex releases can be determined from the results of many single-particle releases.This work is intended to provide context for both (a) the initial stages of a disease outbreak and (b) larger scale (≥ 2 m) disease spread, including distant disease “sparks” (low probability, unexpected disease transmission events that infect remote, susceptible populations). The physics of airborne particulate dispersion inherently constrains airborne disease transmission. As such, this work suggests results that, a priori, may be applicable to many airborne diseases.Model PredictionsModeling predictions of the single-particle transmission kernel suggest that outdoor airborne disease transmission events may occur episodically as the infection probabilities can vary over many orders of magnitude depending on the distance downwind; specific virus, prion, or microorganism; and meteorological conditions.Model results suggest that, under the right conditions, an indoor infected person could spread disease to a similar, or greater, number of people downwind than in the building they occupy. However, the downwind, per-person infection probability is predicted to be lower than the within-building, per-person infection probability. This finding is limited to airborne transmission considerations.This work suggests a new relative disease probability metric for airborne transmitted diseases. This metric, which is distinct from the traditional relative risk metric, is applicable when the rate at which the infectious agent losses infectivity in the atmosphere is ≲ 1 h-1.

scholarly journals A cross-sectional investigation of SARS-CoV-2 seroprevalence and associated risk factors in children and adolescents in the United States

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0259823
Author(s):  
Rebecca E. Levorson ◽  
Erica Christian ◽  
Brett Hunter ◽  
Jasdeep Sayal ◽  
Jiayang Sun ◽  
...  
Keyword(s):  
Risk Factors ◽  
Children And Adolescents ◽  
Disease Transmission ◽  
Specific Antigen ◽  
Significant Risk ◽  
The United States ◽  
Mitigation Strategies ◽  
Metropolitan Region ◽  
Antibody Testing ◽  
Cross Sectional

Background Pediatric SARS-CoV-2 data remain limited and seropositivity rates in children were reported as <1% early in the pandemic. Seroepidemiologic evaluation of SARS-CoV-2 in children in a major metropolitan region of the US was performed. Methods Children and adolescents ≤19 years were enrolled in a cross-sectional, observational study of SARS-CoV-2 seroprevalence from July-October 2020 in Northern Virginia, US. Demographic, health, and COVID-19 exposure information was collected, and blood analyzed for SARS-CoV-2 spike protein total antibody. Risk factors associated with SARS-CoV-2 seropositivity were analyzed. Orthogonal antibody testing was performed, and samples were evaluated for responses to different antigens. Results In 1038 children, the anti-SARS-CoV-2 total antibody positivity rate was 8.5%. After multivariate logistic regression, significant risk factors included Hispanic ethnicity, public or absent insurance, a history of COVID-19 symptoms, exposure to person with COVID-19, a household member positive for SARS-CoV-2 and multi-family or apartment dwelling without a private entrance. 66% of seropositive children had no symptoms of COVID-19. Secondary analysis included orthogonal antibody testing with assays for 1) a receptor binding domain specific antigen and 2) a nucleocapsid specific antigen had concordance rates of 80.5% and 79.3% respectively. Conclusions A much higher burden of SARS-CoV-2 infection, as determined by seropositivity, was found in children than previously reported; this was also higher compared to adults in the same region at a similar time. Contrary to prior reports, we determined children shoulder a significant burden of COVID-19 infection. The role of children’s disease transmission must be considered in COVID-19 mitigation strategies including vaccination.

scholarly journals Mitigation strategies for airborne disease transmission in orchestras using computational fluid dynamics

2021 ◽  
Vol 7 (26) ◽  
pp. eabg4511
Author(s):  
Hayden A. Hedworth ◽  
Mokbel Karam ◽  
Josh McConnell ◽  
James C. Sutherland ◽  
Tony Saad
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Disease Transmission ◽  
Performing Arts ◽  
Mitigation Strategies ◽  
Quantitative Microbial Risk Assessment ◽  
Breathing Zone ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Airborne Disease

The COVID-19 pandemic forced performing arts groups to cancel shows and entire seasons due to safety concerns for the audience and performers. It is unclear to what extent aerosols generated by wind instruments contribute to exposure because their fate is dependent on the airflow onstage. We use transient, second-order accurate computational fluid dynamics (CFD) simulations and quantitative microbial risk assessment to estimate aerosol concentrations and the associated risk and assess strategies to mitigate exposure in two distinct concert venues. Mitigation strategies involved rearranging musicians and altering the airflow by changing HVAC settings, opening doors, and introducing flow-directing geometries. Our results indicate that the proposed mitigation strategies can reduce aerosol concentrations in the breathing zone by a factor of 100, corresponding to a similar decrease in the probability of infection.

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