Virus-laden Aerosols Research Articles

Aerodynamic Size-Dependent Collection and Inactivation of Virus-Laden Aerosol Particles in an Electrostatic Precipitator.

Electrostatic precipitators (ESPs) may enable high particle collection efficiency with minimal pressure drop in HVAC systems. However, studies of pathogen collection and inactivation in ESPs at medium to higher flow rates are limited. Here, a single-stage, wire-plate ESP operated at flow rates of 51 and 85 m3 h-1 was used to study the removal of virus-laden aerosol particles for three different airborne viruses: (1) bovine coronavirus (BCoV), (2) influenza A virus (IAV), and (3) porcine reproductive and respiratory virus (PRRSV). Size-resolved measurements of collection efficiency were obtained using Andersen cascade impactors (ACI) sampling upstream and downstream of the ESP. All measurements were analyzed based on three distinctive but complementary methods: (1) fluorimetry to assess physical collection, (2) RT-qPCR to assess viral RNA concentrations and (3) virus titration to assess virus viability. In general, log reductions by virus titration were highest followed by those from RT-qPCR, and last fluorimetry, suggesting that a portion of virus may be potentially inactivated in flight in the ESP. An effective migration (deposition) velocity ranging from 3.10 to 10.05 cm s-1 was also determined using the spatially resolved measurements of virus collection on the ESP plates.

Effects of table based air curtains on respiratory aerosol exposure risk mitigation at face-to-face meeting setups

Face-to-face meetings on a conference table are a frequent form of communication. The short-range exposure risk of aerosol disease transmission is high in the scenario of susceptible facing the infectious person over the table. We propose a mitigation methodology using the air curtain to reduce direct exposure to virus-laden aerosols. A numerical model was validated with experimental data to simulate the dispersion of aerosols. A dynamic mesh was adopted to consider the head movement of a 3D thermal manikin model. Results show that nodding head increase the potential risk by 74 % compared to motionless. Subsequently, for a single air curtain, placing it in the middle of the table is more effective in preventing risks than on the sides. For double air curtains, increasing the distance between them has a greater risk reduction effect than a shorter distance. Increasing the air velocity or width is more effective than increasing the number of air curtains. A moderate velocity (1 m s−1) works well to reduce the risk of nasal breathing. A higher velocity (2 m s−1) is needed for the coughing scenario. For similar indoor environments, the air curtains on the table can offer active precautions without changing the current ventilation system.

Do ceiling fans in rooms help to reduce or disperse the transmission of breathing aerosols?

The main focus of this study is the transmission of SARS-CoV-2 through virus-laden aerosols in enclosed spaces that utilize ceiling fans. The impact of an air circulation of ceiling fans on virus transmission is not clear. Computational modeling is employed to investigate aerosol transmission within an enclosed space that features ceiling fans. The aerosol concentration is modeled using a transport equation, and the probability of infection distribution across individuals’ breathing zones is assessed. The particle removal efficiency for two ceiling fan speeds of 10 and 35 rad/s is calculated to evaluate the effect of the ceiling fan’s shear flows on the spread of breathing aerosols. The simulated breathing aerosol considers various environmental situations, including thermal gradients, thermally active surface interaction, and deformability. The results indicate that increasing the ceiling fan speed within an enclosed space causes the aerosol cloud to circulate within the room rather than exiting it. Therefore, ceiling fans may not effectively suppress breathing aerosols and could increase transmissibility. Understanding aerosol behavior is essential in reducing the risk of SARS-CoV-2 transmission in enclosed spaces.

Asymmetric aerosol volume transmission: A computational approach toward infection prevention efficiency of face masks

Wearing face masks is considered as one of the infection prevention and control options for respiratory viruses (e.g., SARS-CoV-2) that acts by blocking virus-laden aerosols. It is generally thought that aerosol blockage occurs when air passes through the face mask fabric. We calculated air flows through face masks and through peripheral leakages, based on reported breathing resistance values of face masks (FFP/N95, surgical masks, and cloth masks) and found that most of the inhaled and exhaled air passes through these peripheral leakages. Nevertheless, face masks remain effective as an infection prevention option, because additional calculations showed that the majority of aerosol volume cannot follow the tortuous path of air around the face mask. The filtering efficiency through the peripheral leakages can be described as a function of breathing conditions, vocal activities, the leakage geometry and tortuous pathway, aerosol properties (diameter, composition) and ambient conditions (e.g., evaporation, ventilation). Inclusion of these parameters explains the asymmetric filtering behavior of face masks, i.e., the risk of infection from person A to person B does not necessarily equal the risk of infection from person B to person A. Our findings explain thus why masking an infectious person is more effective than masking an exposed person. Establishing that the tortuous pathway of air around the face mask is the sole contributor to face mask efficiency opens new opportunities for designing safer face masks.

Evaluation of Surrogate Aerosol Experiments to Predict Spreading and Removal of Virus-Laden Aerosols

Estimating the infection risks of indoor environments comprises the assessment of the behavior of virus-laden aerosols, i.e., their spreading, mixing, removal by air purifiers, etc. A promising experimental approach is based on using non-hazardous surrogate aerosols of a similar size, e.g., salt particles, to mimic virus aerosol behavior. This manuscript addresses the issue of how a successful transfer of such experiments can be accomplished. Corresponding experiments in two very different environments, a large community hall and a seminar room, with the optional use of air purifiers in various constellations, are conducted. While high particle concentrations are advantageous in terms of avoiding the influence of background aerosol concentrations, it is shown that the appropriate consideration of aggregation and settling are vital to theoretically describe the experimentally determined course of particle concentrations. A corresponding model equation for a well-mixed situation is derived, and the required parameters are thoroughly determined in separate experiments independently. It is demonstrated that the clean air delivery rates (CADRs) of air purifiers determined with this approach may differ substantially from common approaches which do not explicitly take aggregation into account.

Bio-based ionic liquid filter with enhanced electrostatic attraction for outside filtration and inside collection of viral aerosols

Hazardous biological pathogens in the air pose a significant public environmental health concern as infected individuals emit virus-laden aerosols (VLAs) during routine respiratory activities. Mask-wearing is a key preventive measure, but conventional filtration methods face challenges, particularly in high humidity conditions, where electrostatic charge decline increases the risk of infection. This study introduces a bio-based air filter comprising glycine ionic liquids (GILs) and malleable polymer composite (GILP) with high polarity and functional group density, which are wrapped around a melamine-formaldehyde (MF) resin skeleton, forming a conductive, porous GIL functionized ionic network air filter (GILP@MF). When subjected to low voltage, the GILP@MF composite efficiently captures VLAs including nanoscale virus particles through the enhanced electrostatic attraction, especially in facing high humidity bioaerosols exhaled by human body. The filtration/collection efficiency and quality factor can reach 98.3% and 0.264 Pa−1 at 0.1 m s−1, respectively. This innovative filter provides effective VLA protection and offers potential for non-invasive respiratory virus sampling, advancing medical diagnosis efforts.

A Novel Face Masks and it’s Utility during COVID-19 Pandemic: A Comprehensive Review

In recent decades, the rising frequency of infectious illnesses has presented a severe danger to public health. The Centres for Disease Control and Prevention (CDC) in the United States established that an infected or asymptomatic person wearing a surgical mask shields others from the user. This is because virus-laden aerosols and droplets are thought to be the major mode of transmission between persons. The United States continues to have insufficient control over the spread of SARS-CoV-2, even with the extensive use of masks and other mitigating methods. The public health viewpoint on mask usage, the technical specifications of store-bought and homemade masks, and the most current developments in mask engineering, materials, and disinfection will all be covered in this review. Additionally, the sustainability of mask wear and mask manufacture will be discussed.

The Effect of Singers' Masks on the Impulse Dispersion of Aerosols During Singing.

During the Covid-19 pandemic, singing activities were restricted due to several super-spreading events that have been observed during rehearsals and vocal performances. However, it has not been clarified how the aerosol dispersion, which has been assumed to be the leading transmission factor, could be reduced by masks which are specially designed for singers. Twelve professional singers (10 of the Bavarian Radio-Chorus and two freelancers, seven females and five males) were asked to sing the melody of the ode of joy of Beethoven's 9th symphony "Freude schöner Götterfunken, Tochter aus Elisium" in D-major without masks and afterwards with five different singers' masks, all distinctive in their material and proportions. Every task was conducted after inhaling the basic liquid from an e-cigarette. The aerosol dispersion was recorded by three high-definition video cameras during and after the task. The cloud was segmented and the dispersion was analyzed for all three spatial dimensions. Further, the subjects were asked to rate the practicability of wearing the tested masks during singing activities using a questionnaire. Concerning the median distances of dispersion, all masks were able to decrease the impulse dispersion of the aerosols to the front. In contrast, the dispersion to the sides and to the top was increased. The evaluation revealed that most of the subjects would reject performing a concert with any of the masks. Although, the results exhibit that the tested masks could be able to reduce the radius of aerosol expulsion for virus-laden aerosol particles, there are more improvements necessary to enable the practical implementations for professional singing.

Nosocomial Coronavirus Disease 2019 during 2020-2021: Role of Architecture and Ventilation.

Nosocomial coronavirus disease 2019 (COVID-19) is a major airborne health threat for inpatients. Architecture and ventilation are key elements to prevent nosocomial COVID-19 (NC), but real-life data are challenging to collect. We aimed to retrospectively assess the impact of the type of ventilation and the ratio of single/double rooms on the risk of NC (acquisition of COVID-19 at least 48 h after admission). This study was conducted in a tertiary hospital composed of two main structures (one historical and one modern), which were the sites of acquisition of NC: historical (H) (natural ventilation, 53% single rooms) or modern (M) hospital (double-flow mechanical ventilation, 91% single rooms). During the study period (1 October 2020 to 31 May 2021), 1020 patients presented with COVID-19, with 150 (14.7%) of them being NC (median delay of acquisition, 12 days). As compared with non-nosocomial cases, the patients with NC were older (79 years vs. 72 years; p < 0.001) and exhibited higher mortality risk (32.7% vs. 14.1%; p < 0.001). Among the 150 NC cases, 99.3% were diagnosed in H, mainly in four medical departments. A total of 73 cases were diagnosed in single rooms versus 77 in double rooms, including 26 secondary cases. Measured air changes per hour were lower in H than in M. We hypothesized that in H, SARS-CoV-2 transmission was favored by short-range transmission within a high ratio of double rooms, but also during clusters, via far-afield transmission through virus-laden aerosols favored by low air changes per hour. A better knowledge of the mechanism of airborne risk in healthcare establishments should lead to the implementation of corrective measures when necessary. People's health is improved using not only personal but also collective protective equipment, i.e., ventilation and architecture, thereby reinforcing the need to change institutional and professional practices.

Local control of near-field diffusion of infected respiratory cloud in a room by air-blades

The respiratory cloud of an infective subject contains droplets of mucosalivary fluid carrying pathogens. As this cloud spreads at a certain distance from the emission point, the droplets accumulate and their volume concentration increases in the room unless dilution, adequate ventilation, or filtration reduce it. A susceptible subject, standing a short distance away can be exposed more easily to the infected respiratory cloud, thus inhaling a higher dose of pathogens than someone breathing the mixed air in the room. A local airflow pattern can be employed to reduce this short-distance risk of inhalation and potential contagion. We present experimental and numerical investigations of a novel device acting as a barrier to airborne pathogen diffusion at a short distance. This portable device generates V-shaped air blades in front of the subjects, shifting the respiratory clouds. The air blades are generated by 12 small fans, three on each side of the cube. The air is sucked into the small plenum inside the device body through the bases. By being positioned obliquely on a meeting table, the device acts as a direct barrier to virus-laden aerosols without any filtration. The experimental tests show that the system can reduce the local concentration of aerosol by 63 to 84% at the respiratory position of a subject sitting at a table in front of an infective person. CFD simulation outputs using the Multiphase Eulerian-Lagrangian model show a good agreement with the experimental results. The validated model will be used to extend the range of investigation to different settings and to perform a parametrical analysis of the main design conditions.

Large-scale flow field and aerosol particle transport investigations in a classroom using 2D-Shake-The-Box Lagrangian Particle Tracking

Infections with COVID-19 in enclosed public spaces, where virus-laden aerosol particles can accumulate over time, have significantly contributed to the rapid spread of the virus. It is therefore of great importance to understand the transport and dispersion process of aerosol particles in such spaces, especially against the background of future pandemics. In this work, we present a Lagrangian-Particle-Tracking experiment to assess the mixed convective flow in a classroom with different ventilation strategies. For this purpose, thermal plumes were created by heated dummies, and a collimated LED light-sheet with ∼0.4 m thickness was used for illumination of helium filled soap bubbles (HFSB) acting as passive tracer particles. In this way, the Lagrangian trajectories of the particles were recorded at two approximately 4.2 m × 2.8 m large fields using the novel 2D-Shake-The-Box-Method. As a result, time-resolved trajectories of over 300,000 simultaneously tracked HFSB have been reconstructed, so that both small-scale and large-scale properties of the flow are visualized quantitatively across the entire cross-section of the room. The trajectories show that the thermal plumes create lengthwise circulating vortices, which cannot be destroyed across the entire cross-section of the room by opening or tilting a window. Furthermore, the mixing in the room through the operation of an air purifier is higher compared to opening a window, which suggests that this strategy in combination with its air filtering capability is the most effective strategy to prevent infections.

Numerical simulation of virus-laden aerosol transmission in real human respiratory airways

In this study, the transport of virus-laden aerosols in real human airways is investigated through numerical simulations. Three different breathing modes (nasal, oral, and nasal–oral) are studied to analyze the behavior of the particle deposition in the respiratory airways of humans through realistic anatomical models. Increasing the flow rate typically leads to the augmentation of velocity profiles, turbulence, and pressure changes, specifically expanding the high velocity regions in the pharynx, larynx, and trachea. As a result, the deposition fractions of the total number of aerosols deposited in these regions increase, while a decrease in aerosol deposition is observed in the nasal and oral cavities. For the effects of increasing particle sizes, 2–10 μm particles exhibit a higher degree of clustering in the trachea for the nasal mode, in the larynx for the oral mode, and in the trachea for the nasal–oral mode, compared to the clustering of 1–10 μm particles. Considering the high deposition fraction in the upper airway regions, which are the primary factors contributing to the easy transmission of the virus through casual talking and coughing, the results demonstrate that the highest deposition fraction, exceeding 85%, is observed in the nasal mode with small aerosols ranging from 1 to 2 μm in diameter, and at the lowest flow rate of 15 LPM. In the lower airway regions, targeted drug delivery with the highest deposition fraction in the bronchial regions can be a solution for reducing respiratory diseases, such as asthma and chronic obstructive pulmonary disease, which are caused by inflammatory conditions in the bronchi.

Risk mitigation to healthcare workers against viral and bacterial bioaerosol load in laparoscopic surgical exhaust with a new flow mode in hollow fiber membranes-based filter

Laparoscopy of COVID-19-infected/suspected patients needs to be performed with the utmost care due to the chances of virus carryover through the pneumoperitoneum gas. In this study, polysulfone/polyvinyl-pyrrolidone hollow fiber membranes (HFMs) were fabricated by phase inversion process, and these HFMs were bundled into a module consisting of tortuous, circular-helical arrangement. Further, copper (Cu) and zinc (Zn) nanoparticles (NPs), known to have antimicrobial and antiviral properties, were flow-coated on the lumen side of the HFMs. To test functional efficiency, the modules were challenged with wet aerosol and bioaerosols. Wet aerosol removal efficiency was ∼98%. Bioaerosol-containing bacteria E. coli strain K-12, showed 2.6 log (∼99.8%), and 2.1 log (∼99.3%) removal efficiency for Cu NPs and Zn NPs coated HFMs modules, respectively, and 1.6 log (∼97%) removal for plain (uncoated) HFMs. Bioaerosols containing SARS-CoV-2 surrogate virus (MS2 bacteriophage) showed ∼5–7 log reduction of bacteriophage for plain HFMs, 3.9 log, and 2.3 log reduction for Cu and Zn coated HFMs, respectively. The flow of aerosols entirely through the HFM lumen helps in attaining a low ΔP of < 1 mm Hg, thus rendering its usefulness, particularly for exhausting pneumoperitoneum gases where high upstream pressures could lead to barotrauma. Statement of environmental implicationSurgical smoke is generated during minimally invasive surgical (MIS) procedure such as laparoscopy when electrosurgical devices are used to cut any tissues. This smoke is a hazard as it contains toxic volatile compounds, mutagens, carcinogens, bacteria, and virus-laden aerosols. Infection to healthcare professionals through the bioaerosols containing smoke is well reported in literature. The limitation of using hypochlorite and pleated/HEPA filter, led us to design a low pressure drop bioaerosol filter, which can remove smoke, tissue fragments, and COVID-19 virus. It provides a much safer operation theatre environment during MIS procedures as well as in general for bioaerosol removal.

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.

Rapid Direct Detection of SARS-CoV-2 Aerosols in Exhaled Breath at the Point of Care.

Airborne transmission via virus-laden aerosols is a dominant route for the transmission of respiratory diseases, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Direct, non-invasive screening of respiratory virus aerosols in patients has been a long-standing technical challenge. Here, we introduce a point-of-care testing platform that directly detects SARS-CoV-2 aerosols in as little as two exhaled breaths of patients and provides results in under 60 s. It integrates a hand-held breath aerosol collector and a llama-derived, SARS-CoV-2 spike-protein specific nanobody bound to an ultrasensitive micro-immunoelectrode biosensor, which detects the oxidation of tyrosine amino acids present in SARS-CoV-2 viral particles. Laboratory and clinical trial results were within 20% of those obtained using standard testing methods. Importantly, the electrochemical biosensor directly detects the virus itself, as opposed to a surrogate or signature of the virus, and is sensitive to as little as 10 viral particles in a sample. Our platform holds the potential to be adapted for multiplexed detection of different respiratory viruses. It provides a rapid and non-invasive alternative to conventional viral diagnostics.

Real-time 4D tracking of airborne virus-laden droplets and aerosols

There is currently no real-time airborne virus tracking method, hindering the understanding of rapid virus changes and associated health impacts. Nano-digital in-line holographic microscopy (Nano-DIHM) is a lensless technology that can directly obtain the interference patterns of objects by recording the scattered light information originating from the objects. Here, we provide evidence for real-time physicochemical tracking of virus-laden droplets and aerosols in the air using desktop label-free Nano-DIHM. The virus interference patterns, as single and ensemble particles, were imaged by the Nano-DIHM with 32.5 ms resolution. The next-generation Stingray and Octopus software was used to automate object detection, characterization and classification from the recorded holograms. The detection system was demonstrated to detect active MS2 bacteriophages, inactivated SARS-CoV-2 and RNA fragments, and an MS2 mixture with metallic and organic compounds. This work demonstrates the feasibility of using Nano-DIHM to provide rapid virus detection to improve transmission management in real time.

Numerical investigation of airborne infection risk in an elevator cabin under different ventilation designs

Airborne transmission of SARS-CoV-2 via virus-laden aerosols in enclosed spaces poses a significant concern. Elevators, commonly utilized enclosed spaces in modern tall buildings, present a challenge as the impact of varying heating, ventilation, and air conditioning (HVAC) systems on virus transmission within these cabins remains unclear. In this study, we employ computational modeling to examine aerosol transmission within an elevator cabin outfitted with diverse HVAC systems. Using a transport equation, we model aerosol concentration and assess infection risk distribution across passengers' breathing zones. We calculate the particle removal efficiency for each HVAC design and introduce a suppression effect criterion to evaluate the effectiveness of the HVAC systems. Our findings reveal that mixing ventilation, featuring both inlet and outlet at the ceiling, proves most efficient in reducing particle spread, achieving a maximum removal efficiency of 79.40% during the exposure time. Conversely, the stratum ventilation model attains a mere removal efficiency of 3.97%. These results underscore the importance of careful HVAC system selection in mitigating the risk of SARS-CoV-2 transmission within elevator cabins.

Aerosol exchange between pressure-equilibrium rooms induced by door motion and human movement

It is now widely recognised that aerosol transport is major vector for transmission of diseases such as COVID-19, and quantification of aerosol transport in the built environment is critical to risk analysis and management. Understanding the effects of door motion and human movement on the dispersion of virus-laden aerosols under pressure-equilibrium conditions is of great significance to the evaluation of infection risks and development of mitigation strategies. This study uses novel numerical simulation techniques to quantify the impact of these motions upon aerosol transport and provides valuable insights into the wake dynamics of swinging doors and human movement. The results show that the wake flow of an opening swinging door delays aerosol escape, while that of a person walking out entrains aerosol out of the room. Aerosol escape caused by door motion mainly happens during the closing sequence which pushes the aerosols out. Parametric studies show that while an increased door swinging speed or human movement speed can enhance air exchange across the doorway, the cumulative aerosol exchange across the doorway is not clearly affected by the speeds.

CO2 concentration as an indicator of indoor ventilation performance to control airborne transmission of SARS-CoV-2

BackgroundThe Wells-Riley equation has been extensively used to quantify the infection risk of airborne transmission indoors. This equation is difficult to apply to actual conditions because it requires measurement of the outdoor air supply rate, which vary with time and are difficult to quantify. The method of determining the fraction of inhaled air that has been exhaled previously by someone in a building using a CO2 concentration measurement can solve the limitations of the existing method. Using this method, the indoor CO2 concentration threshold can be determined to keep the risk of infection below certain conditions. MethodsBased on the calculation of the rebreathed fraction, an appropriate mean indoor CO2 concentration and required air exchange rate to control SARS-CoV-2 airborne transmission was calculated. The number of indoor occupants, ventilation rate, and the deposition and inactivation rates of the virus-laden aerosols were considered. The application of the proposed indoor CO2 concentration-based infection rate control was investigated through case studies in school classrooms and restaurants. ResultsIn a typical school classroom environment with 20–25 occupants and an exposure time of 6–8 h, the average indoor CO2 concentration should be kept below 700 ppm to control the risk of airborne infection indoors. The ASHRAE recommended ventilation rate is sufficient when wearing a mask in classrooms. For a typical restaurant with 50–100 occupants and an exposure time of 2–3 h, the average indoor CO2 concentration should be kept below about 900 ppm. Residence time in the restaurant had a significant effect on the acceptable CO2 concentration. ConclusionGiven the conditions of the occupancy environment, it is possible to determine an indoor CO2 concentration threshold, and keeping the CO2 concentration lower than a certain threshold could help reduce the risk of COVID-19 infection.

Fates of Emitted Particles Depending on Mask Wearing Using an Approach Validated Across Spatial Scales.

The spread of emitted potentially virus-laden aerosol particles is known to be highly dependent on whether a mask is worn by an infected person and on the emission scenario, i.e., whether the person is coughing, speaking, or breathing. The aim of this work is to investigate in detail the fates of particles emitted by a person wearing a perfectly fitting, a naturally fitted mask with leakage, and no mask depending on the emission scenario. Therefore, a two-scale numerical workflow is proposed where parameters are carried through from a micro-scale where the fibers of the mask filter medium and the aerosol particles are resolved to a macro-scale and validated by comparison to experimental measurements of fractional filtration efficiency and pressure drop of the filter medium as well as pressure drop of the mask. It turns out that masks reduce the number of both emitted and inhaled particles significantly even with leakage. While without a mask, the person opposite of an infected person is generally at the highest risk of being infected, a mask worn by an infected person speaking or coughing will deflect the flow leading to the fact that the person behind the infected person might inhale the largest number of aerosol particles.