Airborne Disease Transmission Research Articles

Film dosimetry for occupant exposure monitoring within Far-UVC installations.

Far-UVC radiation between 200 and 230 nm is a promising technology for reducing airborne disease transmission. Previous work with far-UVC lamps has demonstrated the efficacy of far-UVC radiation to inactivate bacteria and viruses while presenting minimal human health hazards. While far-UVC intentionally exposes the occupied space, effectively disinfecting air between occupants, installations must still ensure that occupant eye and skin exposure is within the recommended daily limits. This study examines far-UVC-sensitive films for measuring the dose received by occupants within two real-world far-UVC installations. The film is characterized for accuracy, angular response, wavelength response, and sources of uncertainty in film response, and used to obtain individual exposure doses that account for both the non-uniform irradiance and the unique motion of individuals within the space. Dosimetry results using the films, which account for the time-weighted average exposure of an occupant, ranged from 10% to 49% of the maximum calculated stationary dose based on peak irradiance measurements. Results from this study spotlight the need to incorporate time-weighted average considerations into the design and safety assessment of far-UVC installations to ultimately operate far-UVC technology with its full potential to prevent the spread of potentially fatal infectious diseases.

Contribution of Particulates to Airborne Disease Transmission and Severity: A Review.

The emergence of coronavirus disease 2019 (COVID-19) has catalyzed great interest in the spread of airborne pathogens. Airborne infectious diseases are classified into viral, bacterial, and fungal infections. Environmental factors can elevate their transmission and lethality. Air pollution has been reported as the leading environmental cause of disease and premature death worldwide. Notably, ambient particulates of various components and sizes are harmful pollutants. There are two prominent health effects of particles in the atmosphere: (1) particulate matter (PM) penetrates the respiratory tract and adversely affects health, such as heart and respiratory diseases; and (2) bioaerosols of particles act as a medium for the spread of pathogens in the air. Particulates contribute to the occurrence of infectious diseases by increasing vulnerability to infection through inhalation and spreading disease through interactions with airborne pathogens. Here, we focus on the synergistic effects of airborne particulates on infectious disease. We outline the concepts and characteristics of bioaerosols, from their generation to transformation and circulation on Earth. Considering that microorganisms coexist with other particulates as bioaerosols, we investigate studies examining respiratory infections associated with airborne PM. Furthermore, we discuss four factors (meteorological, biological, physical, and chemical) that may impact the influence of PM on the survival of contagious pathogens in the atmosphere. Our review highlights the significant role of particulates in supporting the transmission of infectious aerosols and emphasizes the need for further research in this area.

Evaporation of bacteria-laden surrogate respiratory fluid droplets: On a hydrophilic substrate vs contact-free environment confers differential bacterial infectivity

The transmission of viruses/bacteria causes infection predominantly via aerosols. The transmission mechanism of respiratory diseases is complex, which includes direct or indirect contact, large droplet, and airborne routes apart from close contact transmission. With this premise, two modes of droplet evaporation are investigated to understand its significance in airborne disease transmission; a droplet in a contact-free environment, which evaporates and forms droplet nuclei, and a droplet on a hydrophilic substrate (fomite). The study examines mass transport, the deposition pattern of bacteria in the precipitates, and their survival and virulence. The osmotic pressure increases with the salt concentration, inactivating the bacteria embedded in the precipitates with accelerated evaporation. Furthermore, the bacteria's degree of survival and enhanced pathogenicity are compared for both evaporation modes. The striking differences in pathogenicity are attributed to the evaporation rate, oxygen availability, and reactive oxygen species generation.

Influence of indoor airflow on airborne disease transmission in a classroom

Influence of indoor airflow on airborne disease transmission in a classroom

UV-C Light Intervention as a Barrier against Airborne Transmission of SARS-CoV-2.

SARS-CoV-2 continues to impact human health globally, with airborne transmission being a significant mode of transmission. In addition to tools like vaccination and testing, countermeasures that reduce viral spread in indoor settings are critical. This study aims to assess the efficacy of UV-C light, utilizing the Violett sterilization device, as a countermeasure against airborne transmission of SARS-CoV-2 in the highly susceptible Golden Syrian hamster model. Two cohorts of naïve hamsters were subjected to airborne transmission from experimentally infected hamsters; one cohort was exposed to air treated with UV-C sterilization, while the other cohort was exposed to untreated air. Treatment of air with UV-C light prevented the airborne transmission of SARS-CoV-2 from the experimentally exposed hamster to naïve hamsters. Notably, this protection was sustained over a multi-day exposure period during peak viral shedding by hamsters. These findings demonstrate the efficacy of the UV-C light to mitigate against airborne SARS-CoV-2 transmission. As variants continue to emerge, UV-C light holds promise as a tool for reducing infections in diverse indoor settings, ranging from healthcare facilities to households. This study reinforces the urgency of implementing innovative methods to reduce airborne disease transmission and safeguard public health against emerging biological threats.

Design of a WiFi sensor network to identify transmission zones of respiratory diseases through air quality indicators

infants and postoperative patients. While air extraction and droplet filtration systems are effective in containing these viruses, interconnected ventilation ducts can still facilitate virus transmission in areas with lower viral concentration. This study introduces a Wireless Sensor Network based on WiFi technology, designed to monitor crucial environmental variables such as CO2, TVOC, temperature, and humidity, collectively influencing indoor air quality. Moreover, this network connects to an online server, collaborating with subscribers to store historical data. The stored information aids in identifying patterns and high-risk zones associated with the transmission of respiratory diseases. The outcomes demonstrate a comprehensive, adaptable, and scalable WiFi-based Indoor Air Quality sensor network. Employing the publish-subscribe pattern, the MQTT message transport protocol, and open-access platforms like Streamlit, Supabase, and HiveMQ, along with affordable boards and sensors, this solution offers an innovative, scalable, and cost-effective approach to identifying areas at risk of airborne disease transmission. The system's design prioritizes data precision and reliability, making it a valuable addition to indoor air quality monitoring systems.

CFD Analysis of Airborne Pathogen Disinfection in a UV-C Air Purification Device

Abstract Numerical simulations of the airflow inside a portable air purification device have been carried out. The simplified system geometry is comprised of key components – fans, particle filters and UV lamps for disinfection, which are included in the model. The study investigates the velocity distribution, UV irradiance, and its impact on air disinfection. The effects of the flow rate and UV dose on the purification efficacy have been investigated. The findings provide valuable insights for optimising the design and configuration of air purification devices, and their potential role in reducing the transmission of airborne diseases.

Experimental characterization of exhaled flow dynamics of human breathing and vocalization

During the onging pandemic of COVID-19, there are numerous asymptomatic patients who are infectious. The exhaled droplets from their daily respiratory activities like breathing or speaking can be the sources of airborne disease transmission of COVID-19. The understanding of the airflow dynamics of these respiratory activities may be helpful to develop effective measures to prevent and control the spread of the disease. In this study, the exhaled flows from human breathing and vocalization of specific syllables are characterized using particle image velocimetry (PIV) and smoke visualization. The exhaled flow generated by ten phonemes including vowels, fricatives, affricates, plosives and nasals as well as mouth breathing are studied. The dynamic developments of the airflow processes are described by a series of parameters, including peak velocity, peak velocity time, duration time, propagation velocity and distance. Results show that vocalization of affricates and plosives as well as mouth breathing tend to have higher peak velocities and propagation distances. The evolutions of exhaled flows generated from these respiratory processes are found to have different jet structures, which are related to the stroke ratio (L/D). The flow field of a small L/D only has a pair of dominant vortices. Whereas that of a large L/D presents both a pair of dominant vortex ring and a trailing jet. Certain phoneme (e.g., /t/) is found to display a two-stage jet similar to a cough with the starting jet and an interrupted jet. The characterization of human exhaled flow of this study may be helpful to provide basis of CFD simulations and a better understanding of the spread of airborne diseases from human breathing.

Portable Air Purifiers’ Predicted Efficacy in Mitigating Airborne Pathogen Transmission in an Office Room Featuring Mixing Ventilation

Portable air purifiers have been extensively used to improve indoor air quality and mitigate the transmission of airborne diseases. However, the efficacy of mitigation is strongly affected by the interactions between jet flows of processed air from the air purifiers and the background airflows driven by the ventilation system. Critical factors in this context include the position and capacity of air purifiers and the ventilation rate of the heating ventilation and air-conditioning (HVAC) system. These factors are investigated in this study via computational fluid dynamics (CFD) simulations and the infection probability for different scenarios is quantified using the latest airborne infection predictive model incorporating recent pathological and clinical data for SARS-CoV-2. The results show that the use of air purifiers can significantly reduce the concentration of particulate matter, thus contributing to a generally lower risk of airborne transmission. However, the position of air purifiers affects their overall efficacy remarkably. Comparatively, a central HVAC system is more efficient at removing airborne particles under an equivalent ventilation rate assuming it uses a mixing ventilation scheme.

Quantifying Ventilation Design, Room Layout, and Occupant Activity Parameters during Aerosol-Generating Medical Procedures in Hospitals

The risk of airborne disease transmission in hospital rooms during aerosol-generating medical procedures is known to be influenced by the size of the room, air ventilation rate, input-to-output flow ratio, vent surface area, and vent location. However, quantitative recommendations for each ventilation design parameter are scarce. Moreover, room layout and occupant activity parameters, such as furniture locations and healthcare worker movement, are often omitted from studies on airborne disease transmission in hospital settings. As a result, the development of policies and technologies aimed at mitigating airborne disease transmission in hospitals has been limited. To address this shortfall, this study is aimed at first characterizing existing ventilation, room layout, and occupancy parameters in hospital rooms where aerosol generation medical procedures (AGMPs) occur and then testing the hypotheses that ventilation, room layout, and occupancy parameters vary significantly between hospital rooms and, in some cases, with time. Information on AGMPs was collected via a survey circulated to healthcare workers within British Columbia’s Interior Health Authority (IHA), while hospital room and ventilation system information was collected by reviewing drawing packages of 37 IHA hospital rooms. The survey results indicate that AGMPs commonly occur in trauma, ICU, or general ward rooms with positive or negative pressure ventilation systems. Statistical tests, with room type (trauma, ICU, or general), room pressure (positive or negative), and/or time as independent variables, show that variables relating to ventilation (number of supply vents, supply and exhaust vent location, ventilation rate, and supply and exhaust area) and room layout (congestion score, room volume, light area, and number of lights) vary with room type but not with room pressure. Occupant activity variables (number of workers, number of moving workers, and speed score) also vary with room type, although to differing extent with room pressure and time. The survey and drawing review data presented in this study can help guide systematic comparisons of mitigative technologies as well as parametric investigations on how room layout, ventilation, and operational parameters influence airborne disease spread. This is a crucial first step in achieving quantitative and clinically relevant recommendations for mitigating airborne disease transmission in healthcare settings.

A quantitative evaluation of aerosol generation during cardiopulmonary resuscitation.

It is unclear if cardiopulmonary resuscitation is an aerosol-generating procedure and whether this poses a risk of airborne disease transmission to healthcare workers and bystanders. Use of airborne transmission precautions during cardiopulmonary resuscitation may confer rescuer protection but risks patient harm due to delays in commencing treatment. To quantify the risk of respiratory aerosol generation during cardiopulmonary resuscitation in humans, we conducted an aerosol monitoring study during out-of-hospital cardiac arrests. Exhaled aerosol was recorded using an optical particle sizer spectrometer connected to the breathing system. Aerosol produced during resuscitation was compared with that produced by control participants under general anaesthesia ventilated with an equivalent respiratory pattern tocardiopulmonary resuscitation. A porcine cardiac arrest model was used to determine the independent contributions of ventilatory breaths, chest compressions and external cardiac defibrillation to aerosol generation. Time-series analysis of participants with cardiac arrest (n = 18) demonstrated a repeating waveform of respiratory aerosol that mapped to specific components of resuscitation. Very high peak aerosol concentrations were generated during ventilation of participants with cardiac arrest with median (IQR [range]) 17,926 (5546-59,209 [1523-242,648]) particles.l-1 , which were 24-fold greater than in control participants under general anaesthesia (744 (309-2106 [23-9099]) particles.l-1 , p < 0.001, n = 16). A substantial rise in aerosol also occurred with cardiac defibrillation and chest compressions. In a complimentary porcine model of cardiac arrest, aerosol recordings showed a strikingly similar profile to the human data. Time-averaged aerosol concentrations during ventilation were approximately 270-fold higher than before cardiac arrest (19,410 (2307-41,017 [104-136,025]) vs. 72 (41-136 [23-268]) particles.l-1 , p = 0.008). The porcine model also confirmed that both defibrillation and chest compressions generate high concentrations of aerosol independent of, but synergistic with, ventilation. In conclusion, multiple components of cardiopulmonary resuscitation generate high concentrations of respiratory aerosol. We recommend that airborne transmission precautions are warranted in the setting of high-risk pathogens, until the airway is secured with an airway device and breathing system with a filter.

Investigating the impact of gaspers on airborne disease transmission in an economy-class aircraft cabin with personalized displacement ventilation

Overhead gaspers provide directional fresh airflow, and thus affect the local airflow pattern and contaminant distribution. To investigate the impact of gaspers on airborne disease transmission in an aircraft cabin with a personalized displacement ventilation system, numerical calculations were conducted in a seven-row, single-aisle, fully occupied, economy-class aircraft cabin with the computational fluid dynamics (CFD) simulation method. We first investigated the impact of source gasper direction and flow rate on the airborne transmission near the contaminant source. We then investigated the protective effect of the receptor's gasper. For a source passenger's gasper, the direction and flow rate of the gasper flow either increased or decreased the air contaminant transmission to other passengers. Directing the source gasper to the abdomen with a medium flow rate performed best by reducing the receptors' mean exposure index by at least 45%, as this approach minimized the contaminant circulation in the cabin. Turning on a receptor passenger's gasper could be an effective strategy to protect the receptor, and the working mechanism was revealed. The gasper-induced jet flow entrained the surrounding air into the jet region, and the protective effect was related to the contaminant concentration at ceiling level. With a suitable gasper direction and flow rate, the gasper jet formed a virtual barrier between the source passenger and the receptor. When the contaminants were transported upwards to a receptor's breathing zone, turning on the receptor's gasper reduced the contaminant concentration, since the downward gasper jet altered the airflow pattern in front of the receptor.

The relationship between ventilation rates in schools and the indoor airborne transmission potential of COVID-19

ABSTRACT The requirement for natural ventilation strategies in classrooms to perform in respect to both their inherent and adaptive capacity is necessary to mitigate the risk of transmission associated with infectious airborne pathogens such as COVID-19. This paper assesses the performance of ten classrooms considering (a) the designed versus actual ventilation capacity; (b) the probability of airborne disease transmission by unit time resulting from calculated ventilation rates and (c) the reduction of transmission risk associated with mask wearing by all occupants. Monitored air changes per hour (ACH) range from 0.26–1.7, demonstrating that none of the classrooms meet designed ventilation rate whilst in operation. If the designed ventilation rate of 5 ACH were to be achieved, it would represent an infection risk of less than 1% during standard class durations and 5% over an 8-hour school day. The minimum achieved ventilation rate represents an infection risk of 7–12% (per class) and 75–100% (per school day) dependent on classroom specific parameters. Protection is afforded by the wearing of masks within the indoor school setting. During specified class durations in settings with sub-optimal ventilation rates, probability of infection can be reduced from 7–12% to 1–5%. Over an 8-hour school day, probability of infection can be reduced from 75–100% to 18–43%. These reductions are possible dependent on mask choice.

Preparing patients diagnosed with ESKD for climate-driven Atlantic hurricanes

IntroductionPersons diagnosed with end-stage kidney disease (ESKD) who require in-center hemodialysis are among the most vulnerable patients in this era of compounding disasters. Climate change is making Atlantic hurricanes stronger and wetter, with a tendency to stall at the time of landfall, resulting in more powerful and damaging storms that may disrupt dialysis and clinical services for ESKD patients. COVID-19 and airborne disease transmission complicates hurricane evacuation and sheltering. This complex risk landscape requires tailored approaches to disaster preparedness for patients, clinicians, and dialysis providers. MethodsWe interviewed dialysis providers about their 2022 Hurricane Ian experience. We developed a survey that examines ESKD patients’ hurricane threat appraisal, adaptation appraisal, hurricane experience, and disaster preparedness (household preparedness, COVID-19 prevention, ESKD-specific preparedness). ResultsDialysis providers have developed elaborate strategies for warning, preparing, and predialyzing their patients when a hurricane is approaching. They prestage tanker trucks with pure water and with diesel fuel to power the auxiliary generators to provide electricity. Among 232 dialysis centers closed on the day when Hurricane Ian made landfall, 50% were operational 2 days poststorm and 99% were operational 5 days poststorm. Patient preparedness survey results will be presented. DiscussionCompared with other medically vulnerable patient populations, patients with ESKD are disaster-prepared and supported by their network of dialysis providers to maintain or rapidly restart their life-sustaining treatments. ConclusionsMultilayered, climate-driven disaster risks amplify the urgency for developing effective approaches for safeguarding patients with ESKD, their caregivers, their providers, and their care systems.

Tolerance fuzzy graphs

Tolerance graphs were introduced in 1982 by M. C. Golumbic and C. L. Monma as a generalization of interval graphs. In this paper, we introduce tolerance fuzzy graphs as a generalization of tolerance graphs, and apply them to a modeling of a transmission of airborne diseases.

Reconciling Airborne Disease Transmission Concerns with Energy Saving Requirements: The Potential of UV-C Pathogen Deactivation and Air Distribution Optimization

The COVID-19 pandemic caused a paradigm shift in our way of using heating, ventilation, and air-conditioning (HVAC) systems in buildings. In the early stages of the pandemic, it was indeed advised to reduce the reuse and thus the recirculation of indoor air to minimize the risk of contamination through inhalation of virus-laden aerosol particles emitted by humans when coughing, sneezing, speaking, or breathing. However, such recommendations are not compatible with energy saving requirements stemming from climate change and energy price increase concerns, especially in winter and summer when the fraction of outdoor air supplied to the building needs to be significantly heated or cooled down. In this experimental study, we aim at providing low-cost and low-energy solutions to modify the ventilation strategies currently used in many buildings to reduce the risk of respiratory disease transmission. Measurements of the indoor air bacterial concentration in a typical office building reveal that ultraviolet germicidal irradiation (UVGI) modules added to the HVAC system are very efficient at inactivating pathogens present in aerosols, leading to indoor concentrations as low as outdoor concentrations, even with significant indoor air recirculation. Moreover, measurements of the CO2 and aerosol air concentration reveal that, with air supply vents placed in the ceiling, placing the air exhaust vents near the floor instead of on the ceiling can improve the ventilation capacity in terms of effective flow rate, with significant consequences in terms of energy savings.

The influence of LEED enhanced indoor air quality credit achievement on COVID-related school closures

School closures during the COVID-19 pandemic have highlighted the importance of in-person learning on child health and wellness. Improving indoor air quality (IAQ) is a critical undertaking to keep children in school during outbreak events. Our primary objective was to evaluate the impact of Enhanced IAQ credit achievement among LEED-certified schools on the ability to remain open during the pandemic. In this analysis, schools that achieved LEED Enhanced IAQ credits for increased ventilation or outdoor air delivery monitoring were assigned to the treatment group; LEED schools without these credits were in the control group. We used LASSO regression to select potential confounders for treatment models. Inverse treatment probability weights were used to control for confounding in mixed effects Poisson models in which the response variable was the number of COVID-related school closure days during the 2021-22 academic year. Although effect estimates for the treatment were not significant, they were consistently in the inverse direction (incidence rate ratio (IRR) [95% CI]: 0.90 [0.80, 1.01]). Models may have lacked power to detect significance due to many schools having zero COVID-related closures during the 2021-22 academic year. An important secondary finding was a 53% decrease in COVID-related closure days (95% CI: 7%–77%) associated with a 10% increase in county residents who reported ‘Always’ using a mask in public. This study contributes to the current understanding of the indoor environment and airborne disease transmission. Efforts to monitor and improve IAQ in schools are important avenues to support community, student, and staff health.

Turbulence characterization of instantaneous airflow above passengers with different air distribution systems in a commercial airliner cabin

The environment inside airliner cabins has attracted increasing attention. Instantaneous airflow, as one of the fundamental parameters of airflow field, affects aspects of the airliner cabin environment such as occupant comfort and airborne disease transmission. This study evaluated the characteristics of instantaneous airflow in airliner cabins with different ventilation systems (mixing ventilation and displacement ventilation) and focused on the region above passengers' heads, where complex turbulence characteristics are found. This investigation used ultrasonic anemometers for measurements at ten selected points above passengers' heads. The energy ratio on the low-frequency scale with mixing ventilation was greater than that with displacement ventilation. The instantaneous airflow with mixing ventilation was close to that of natural wind, while the instantaneous airflow with displacement ventilation was close to that of mechanical wind. Compared with mixing ventilation, displacement ventilation produced a smaller vortex length and a shorter residence time. Moreover, there was no long-term vortex in the flow field under displacement ventilation, and therefore, pollutants would be discharged more quickly from the cabin. In addition, this paper distinguishes the spatial and temporal turbulence scales of mixing and displacement ventilation, thus providing a reference for the selection of grid size and time steps in computational fluid dynamics simulations.

Energy Efficiency and Optimization Strategies in a Building to Minimize Airborne Infection Risks

Heating, ventilation, and air conditioning (HVAC) systems play a crucial role in either increasing or decreasing the risk of airborne disease transmission. High ventilation, for instance, is a common method used to control and reduce the infection risk of airborne diseases such as COVID-19. On the other hand, high ventilation will increase energy consumption and cost. This paper proposes an optimal HVAC controller to assess the trade-off between energy consumption and indoor infection risk of COVID-19. To achieve this goal, a nonlinear model predictive controller (NMPC) is designed to control the HVAC systems of a university building to minimize the risk of COVID-19 transmission while reducing building energy consumption. The NMPC controller uses dynamic models to predict future outputs while meeting system constraints. To this end, a set of dynamic physics-based models are created to capture heat transfer and conservation of mass, which are used in the NMPC controller. Then, the developed models are experimentally validated by conducting experiments in the ETLC building at the University of Alberta, Canada. A classroom in the building is equipped with a number of sensors to measure indoor and outdoor environmental parameters such as temperature, relative humidity, and CO2 concentration. The validation results show that the model can predict room temperature and CO2 concentration by 0.8%, and 2.4% mean absolute average errors, respectively. Based on the validated models, the NMPC controller is designed to calculate the optimal airflow and supply air temperature for every 15 min. The results for real case studies show that the NMPC controller can reduce the infection risk of COVID-19 transmission below 1% while reducing energy consumption by 55% when compared to the existing building controller.

Simulation-based trade-off modeling for indoor infection risk of airborne diseases, energy consumption, and thermal comfort

The transmission of airborne diseases indoors represents a significant challenge to public health. While enhancing ventilation can mitigate infection risks, it simultaneously escalates building energy consumption and alters human thermal comfort. There is limited understanding about the intricate interplay among 1) human health measured as exposure to pathogens and infection risk, 2) building energy consumption as a result of different heating, ventilation, and air conditioning (HVAC) control strategies, and 3) human thermal comfort in different climate zones. This research developed a modeling framework to evaluate the trade-offs among health, energy, and human thermal comfort and conducted simulations using school building data, considering a variety of parameters in temperature, humidity, and ventilation control. Key findings revealed that indoor temperature profoundly influences infection risk, energy consumption, and thermal comfort. Ventilation rate governs the variations of infection risks and building energy usage, while indoor relative humidity demonstrated negligible impacts. Notably, thermal comfort and low infection risk can be concurrently realized, albeit at the expense of high energy consumption. Comparing the optimal and worst environment settings in a typical U.S. climate zone, a 43% decrease in infection risks and a 61% increase in thermal comfort are observed, accompanied by an over 70% increase in energy consumption. The influences and trade-offs among infection risks, energy consumption, and thermal comfort are additionally modulated by climate characteristics.