Virus diffusion in isolation rooms

Anomalous fluctuations of extremes in many-particle diffusion

In many-particle diffusions, particles that move the furthest and fastest can play an outsized role in physical phenomena. A theoretical understanding of the behavior of such extreme particles is nascent. A classical model, in the spirit of Einstein's treatment of single-particle diffusion, has each particle taking independent homogeneous random walks. This, however, neglects the fact that all particles diffuse in a common and often inhomogeneous environment that can affect their motion. A more sophisticated model treats this common environment as a space-time random biasing field which influences each particle's independent motion. While the bulk (or typical particle) behavior of these two models has been found to match to high degree, recent theoretical work of G. Barraquand and I. Corwin, Probab. Theory Relat. Fields 167, 1057 (2017)0178-805110.1007/s00440-016-0699-z and G. Barraquand and P. Le Doussal, J. Phys. A: Math. Theor. 53, 215002 (2020)1751-811310.1088/1751-8121/ab8b39 on a one-dimensional exactly solvable version of this random environment model suggests that the extreme behavior is quite different between the two models. We transform these asymptotic (in system size and time) results into physically applicable predictions. Using high-precision numerical simulations we reconcile different asymptotic phases in a manner that matches numerics down to realistic system sizes, amenable to experimental confirmation. We characterize the behavior of extreme diffusion in the random environment model by the presence of a new phase with anomalous fluctuations related to the Kardar-Parisi-Zhang universality class and equation.

Evaluation of SARS-CoV-2 transmission in COVID-19 isolation wards: On-site sampling and numerical analysis

Although airborne transmission has been considered as a possible route for the spread of SARS-CoV-2, the role that aerosols play in SARS-CoV-2 transmission is still controversial. This study evaluated the airborne transmission of SARS-CoV-2 in COVID-19 isolation wards at Prince of Wales Hospital in Hong Kong by both on-site sampling and numerical analysis. A total of 838 air samples and 1176 surface samples were collected, and SARS-CoV-2 RNA was detected using the RT-PCR method. Testing revealed that 2.3% of the air samples and 9.3% of the surface samples were positive, indicating that the isolation wards were contaminated with the virus. The dispersion and deposition of exhaled particles in the wards were calculated by computational fluid dynamics (CFD) simulations. The calculated accumulated number of particles collected at the air sampling points was closely correlated with the SARS-CoV-2 positive rates from the field sampling, which confirmed the possibility of airborne transmission. Furthermore, three potential intervention strategies, i.e., the use of curtains, ceiling-mounted air cleaners, and periodic ventilation, were numerically investigated to explore effective control measures in isolation wards. According to the results, the use of ceiling-mounted air cleaners is effective in reducing the airborne transmission of SARS-CoV-2 in such wards.

Ventilation Performance Evaluation of a Negative-Pressurized Isolation Room for Emergency Departments

Due to the emergence of COVID-19 becoming a significant pandemic worldwide, hospitals are expected to be capable and flexible in responding to the pandemic situation. Moreover, as frontline healthcare staff, emergency department (ED) staff have a high possibility of exposure risk to infectious airborne. The ED isolation room will possibly and effectively isolate the infected patient, therefore safekeeping frontline healthcare staff and controlling the outbreak. However, there is still limited knowledge available regarding isolation room facilities specifically for the emergency department. In this study, field measurement is conducted in an ED isolation room located in Taiwan. CFD simulation is employed to simulate and investigate the airflow and airborne contaminant distribution. Instead of high air-change rates (ACH) that purposes for dilution, this study proposes the arrangement of exhaust air grilles to improve the contaminant removal. The results reveal that the exhaust air grille placed behind the patient’s head is optimized to dilute airborne contaminants.

Aerodynamic analysis of hospital ventilation according to seasonal variations. A simulation approach to prevent airborne viral transmission pathway during Covid-19 pandemic

During the Covid-19 pandemic, location of the SARS-CoV-2 infected patients inside the hospital is a major issue to prevent viral cross-transmission. The objective of this study was to evaluate the risk of contamination through aerosol by using a global approach of the multiple environmental parameters to simulate, including seasonal context. A computational fluid dynamic (CFD) simulation based on the Lattice Boltzmann Method approach was used to predict airflow on the entire floor of a private hospital in Paris. The risk of contamination outside the rooms was evaluated by using a water vapor mass fraction tracker. Finally, the air contamination was estimated by a "cough model" producing several punctual emissions of contaminated air from potentially infected patients. In a winter configuration, the simulation showed a well-balanced ventilation on the floor and especially inside the rooms. After cough emissions from COVID-positive rooms, no significant contamination was observed in the circulation area, public waiting space and nurse office. On the contrary, in a summer configuration, the temperature difference due to the impact of the sun radiation between both sides of the building created additional air transport increasing the contamination risk in neighboring rooms and public spaces. Airborne spread was limited to rooms during winter conditions. On the contrary, during summer conditions, market airflow with potentially contaminated air coming from rooms located on the side of the building exposed to solar radiation was evidenced. These observations have implications to locate infected patients inside the building and for the conception of future health care structures.

Consequences of Migrating U.S. Contagious Facilities Into General Hospitals, 1900-1950

Until the 1880s, hospitals excluded contagious disease patients from admission because of the danger they posed to other patients; by the 1950s, contagious disease care had literally moved into the general hospital. This article correlates the changing isolation facility designs with changing disease incidence and prevention strategies. It argues that isolation moved into the hospital in stages that have consequence for isolation facility design today. Between the 1890s and 1940s, contagious disease care shifted from remote isolation hospitals (commonly known as pest houses) to separate contagious disease hospitals, to contagious disease "units" adjacent to or within a general hospital facility, and to isolation rooms included in nursing units. The architectural history of isolation facility designs shows that the integration of isolation facilities into general hospitals relied on the success of new aseptic nursing procedures that prevented contact transmission but which downgraded the need for spatial separation to prevent airborne transmission. In the second half of the 20th century, federal funding and standards made isolation rooms in the hospital the norm. This migration coincided with a historically unprecedented reduction in contagious disease incidence produced by successful vaccines and antibiotics. By the 1980s, the rise of new and antibiotic resistant diseases led to extensive redesigns of the in-house isolation rooms to make them more effective. This article suggests that it is time to rethink isolation not just at the detail level but in terms of its location in relation to the general hospital.

Performance Improvement of a Negative-Pressurized Isolation Room for Infection Control

Negative-pressurized isolation rooms have been approved effectively and applied widely for infectious patients. However, the outbreak of COVID-19 has led to a huge demand for negative-pressurized isolation rooms. It is critical and essential to ensure infection control performance through best practice of ventilation systems and optimum airflow distribution within isolation rooms. This study investigates a retrofitting project of an isolation room to accommodate COVID-19 patients. The field measurement has been conducted to ensure the compliance with the design specification from the CDC of Taiwan. The pressure differentials between negative-pressurized isolation rooms and corridor areas should be at least 8 Pa, while the air change rate per hour (ACH) should be 8–12 times. Computational fluid dynamics (CFD) is applied to evaluate the ventilation performance and contamination control. Different layout arrangements of exhaust air have been proposed to enhance the ventilation performance for infection control. A simple projected air-jet curtain has been proposed in the simulation model to enhance extra protection of medical staff. The resulting ventilation control revealed that the contamination control can be improved through the minor adjustment of exhaust air arrangement and the application of an air-jet curtain.

A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet-droplet interactions

Previous studies reported that specially designed ventilation systems provide good air quality and safe environment by removing airborne droplets that contain viruses expelled by infected people. These water droplets can be stable in the environment and remain suspended in air for prolonged periods. Encounters between droplets may occur and droplet interactions should be considered. However, the previous studies focused on other physical phenomena (air flow, drag force, evaporation) for droplet transport and neglected droplet interactions. In this work, we used computational fluid dynamics (CFD) to simulate the transport and fate of airborne droplets expelled by an asymptomatic person and considered droplet interactions. Droplet drag with turbulence for prediction of transport and fate of droplets indicated that the turbulence increased the transport of 1 µm droplets, whereas it decreased the transport of 50 µm droplets. In contrast to only considering drag and turbulence, consideration of droplet interactions tended to increase both the transport and fate. Although the length scale of the office is much larger than the droplet sizes, the droplet interactions, which occurred at the initial stages of release when droplet separation distances were shorter, had a significant effect in droplet fate by considerably manipulating the final locations on surfaces where droplets adhered. Therefore, it is proposed that when an exact prediction of transport and fate is required, especially for high droplet concentrations, the effects of droplet interactions should not be ignored.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s11783-021-1465-8 and is accessible for authorized users.

Modeling of aerosol transmission of airborne pathogens in ICU rooms of COVID-19 patients with acute respiratory failure

The COVID-19 pandemic has generated many concerns about cross-contamination risks, particularly in hospital settings and Intensive Care Units (ICU). Virus-laden aerosols produced by infected patients can propagate throughout ventilated rooms and put medical personnel entering them at risk. Experimental results found with a schlieren optical method have shown that the air flows generated by a cough and normal breathing were modified by the oxygenation technique used, especially when using High Flow Nasal Canulae, increasing the shedding of potentially infectious airborne particles. This study also uses a 3D Computational Fluid Dynamics model based on a Lattice Boltzmann Method to simulate the air flows as well as the movement of numerous airborne particles produced by a patient's cough within an ICU room under negative pressure. The effects of different mitigation scenarii on the amount of aerosols potentially containing SARS-CoV-2 that are extracted through the ventilation system are investigated. Numerical results indicate that adequate bed orientation and additional air treatment unit positioning can increase by 40% the number of particles extracted and decrease by 25% the amount of particles deposited on surfaces 45s after shedding. This approach could help lay the grounds for a more comprehensive way to tackle contamination risks in hospitals, as the model can be seen as a proof of concept and be adapted to any room configuration.

Virions and respiratory droplets in air: Diffusion, drift, and contact with the epithelium

Some infections, including e.g. influenza and currently active COVID 19, may be transmitted via air during sneezing, coughing, and talking. This pathway occurs via diffusion and gravity-induced drift of single virions and respiratory droplets consisting primarily of water, including small fraction of nonvolatile matter, and containing virions. These processes are accompanied by water evaporation resulting in reduction of the droplet size. The manifold of information concerning these steps is presented in textbooks and articles not related to virology and the focus is there frequently on biologically irrelevant conditions and/or droplet sizes. In this brief review, we systematically describe the behavior of virions and virion-carrying droplets in air with emphasis on various regimes of diffusion, drift, and evaporation, and estimate the rates of all these steps under virologically relevant conditions. In addition, we discuss the kinetic aspects of the first steps of infection after attachment of virions or virion-carrying droplets to the epithelium, i.e., virion diffusion in the mucus and periciliary layers, penetration into the cells, and the early stage of replication. The presentation is oriented to virologists who are interested in the corresponding physics and to physicists who are interested in application of the physics to virology.

The role of computational fluid dynamics tools on investigation of pathogen transmission: Prevention and control

Transmission mechanics of infectious pathogen in various environments are of great complexity and has always been attracting many researchers' attention. As a cost-effective and powerful method, Computational Fluid Dynamics (CFD) plays an important role in numerically solving environmental fluid mechanics. Besides, with the development of computer science, an increasing number of researchers start to analyze pathogen transmission by using CFD methods. Inspired by the impact of COVID-19, this review summarizes research works of pathogen transmission based on CFD methods with different models and algorithms. Defining the pathogen as the particle or gaseous in CFD simulation is a common method and epidemic models are used in some investigations to rise the authenticity of calculation. Although it is not so difficult to describe the physical characteristics of pathogens, how to describe the biological characteristics of it is still a big challenge in the CFD simulation. A series of investigations which analyzed pathogen transmission in different environments (hospital, teaching building, etc) demonstrated the effect of airflow on pathogen transmission and emphasized the importance of reasonable ventilation. Finally, this review presented three advanced methods: LBM method, Porous Media method, and Web-based forecasting method. Although CFD methods mentioned in this review may not alleviate the current pandemic situation, it helps researchers realize the transmission mechanisms of pathogens like viruses and bacteria and provides guidelines for reducing infection risk in epidemic or pandemic situations.

Transmission of pathogen-laden expiratory droplets in a coach bus

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

An Evolutionary Perspective of Virus Propagation

This paper presents an evolutionary algorithm that simulates simplified scenarios of the diffusion of an infectious disease within a given population. The proposed evolutionary epidemic diffusion (EED) computational model has a limited number of variables and parameters, but is still able to simulate a variety of configurations that have a good adherence to real-world cases. The use of two space distances and the calculation of spatial 2-dimensional entropy are also examined. Several simulations demonstrate the feasibility of the EED for testing distinct social, logistic and economy risks. The performance of the system dynamics is assessed by several variables and indices. The global information is efficiently condensed and visualized by means of multidimensional scaling.

Effects of indoor environmental parameters related to building heating, ventilation, and air conditioning systems on patients' medical outcomes: A review of scientific research on hospital buildings

The indoor environment of a mechanically ventilated hospital building controls infection rates as well as influences patients' healing processes and overall medical outcomes. This review covers the scientific research that has assessed patients' medical outcomes concerning at least one indoor environmental parameter related to building heating, ventilation, and air conditioning (HVAC) systems, such as indoor air temperature, relative humidity, and indoor air ventilation parameters. Research related to the naturally ventilated hospital buildings was outside the scope of this review article. After 1998, a total of 899 papers were identified that fit the inclusion criteria of this study. Of these, 176 papers have been included in this review to understand the relationship between the health outcomes of a patient and the indoor environment of a mechanically ventilated hospital building. The purpose of this literature review was to summarize how indoor environmental parameters related to mechanical ventilation systems of a hospital building are impacting patients. This review suggests that there is a need for future interdisciplinary collaborative research to quantify the optimum range for HVAC parameters considering airborne exposures and patients' positive medical outcomes.

Assessment of displacement ventilation systems in airborne infection risk in hospital rooms

Efficient ventilation in hospital airborne isolation rooms is important vis-à-vis decreasing the risk of cross infection and reducing energy consumption. This paper analyses the suitability of using a displacement ventilation strategy in airborne infection isolation rooms, focusing on health care worker exposure to pathogens exhaled by infected patients. The analysis is mainly based on numerical simulation results obtained with the support of a 3-D transient numerical model validated using experimental data. A thermal breathing manikin lying on a bed represents the source patient and another thermal breathing manikin represents the exposed individual standing beside the bed and facing the patient. A radiant wall represents an external wall exposed to solar radiation. The air change efficiency index and contaminant removal effectiveness indices and inhalation by the health care worker of contaminants exhaled by the patient are considered in a typical airborne infection isolation room set up with three air renewal rates (6 h-1, 9 h-1 and 12 h-1), two exhaust opening positions and two health care worker positions. Results show that the radiant wall significantly affects the air flow pattern and contaminant dispersion. The lockup phenomenon occurs at the inhalation height of the standing manikin. Displacement ventilation renews the air of the airborne isolation room and eliminates the exhaled pollutants efficiently, but is at a disadvantage compared to other ventilation strategies when the risk of exposure is taken into account.

Strict Isolation

Strict isolation: suspected highly infectious and transmissible virulent and pathogenic microbes, highly resistant bacterial strains and agents that are not accepted in any form of distribution in the society or in the environment. Examples are completely resistant Mycobacterium tuberculosis, viral haemorrhagic fevers like Ebola and Lassa, pandemic severe influenza and coronavirus like SARS, MERS, etc. In most countries, strict isolation is a rarely used isolation regime but should be a part of the national preparedness plan. For instance, in Norway, strict isolation has not been used for the last 50–60 years, except for one case of imported Ebola infection in 2014. Patients in need of strict isolation should be placed in a separate isolation ward or building.

Infection spread by contact, droplet and airborne infection, aerosols, re-aerosols, airborne microbe-carrying particles, skin cells, dust, droplets and droplet nuclei. At the same time, it is always contact transmission (contaminated environment, equipment, textiles and waste).

The source of infection is usually a patient but may also be a symptomless carrier or a zoonotic disease.

Background Information: Isolation Routines

The isolation of patients with suspected or documented infections—to not spread to others—has been discussed for hundreds of years. Guidelines are many, methods are different, attitudes show vide variations, routines and procedures are still changing, regulations by law may be absent, and some healthcare professionals may be afraid of adverse outcomes of isolation [1–44]. Microbes that are spread in the environment, on the hands and equipment are invisible. The invisible agent does not call on attention before the infection; clinical disease, hospital infection or nosocomial infection is a factum that can be registered [23, 28, 29, 35–37]. How to stop the transmission is often “to believe and not believe” in infection control.

Protection of Upper Respiratory Tract, Mouth and Eyes

Pathogenic bacteria and viruses may invade via upper and lower respiratory tract and via eye mucosa. When an infected person coughs or sneezes heavily, small, invisible droplets with the infective agent may reach a good distance from the source. By using the right form of protection at the right time, infection and disease are prevented. The present chapter is focused on the protection against airborne infections.

Estimating finite-population reproductive numbers in heterogeneous populations

The basic reproductive number, R0, is one of the most important epidemiological quantities. R0 provides a threshold for elimination and determines when a disease can spread or when a disease will die out. Classically, R0 is calculated assuming an infinite population of identical hosts. Previous work has shown that heterogeneity in the host mixing rate increases R0 in an infinite population. However, it has been suggested that in a finite population, heterogeneity in the mixing rate may actually decrease the finite-population reproductive numbers. Here, we outline a framework for discussing different types of heterogeneity in disease parameters, and how these affect disease spread and control. We calculate “finite-population reproductive numbers” with different types of heterogeneity, and show that in a finite population, heterogeneity has complicated effects on the reproductive number. We find that simple heterogeneity decreases the finite-population reproductive number, whereas heterogeneity in the intrinsic mixing rate (which affects both infectiousness and susceptibility) increases the finite-population reproductive number when R0 is small relative to the size of the population and decreases the finite-population reproductive number when R0 is large relative to the size of the population. Although heterogeneity has complicated effects on the finite-population reproductive numbers, its implications for control are straightforward: when R0 is large relative to the size of the population, heterogeneity decreases the finite-population reproductive numbers, making disease control or elimination easier than predicted by R0.

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Outline a framework for discussing the different types of heterogeneity.

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Found simple expressions for each of the four different types of heterogeneity and heterogeneity in intrinsic mixing.

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Showed heterogeneity in finite populations is more complicated than previously thought.

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Showed that heterogeneity in a finite population makes control easier than predicted by R0 and the homogeneous finite-population reproductive number.

Study on the interzonal migration of airborne infectious particles in an isolation ward using benign bacteria

Negative pressure isolation wards are essential infection control facilities against airborne transmissible diseases. Airborne infectious particles are supposed to be contained in the isolation room. However, negative pressure may break down by door-opening action or by human movement. Understanding the interzonal transport of airborne infectious particles in the isolation wards can aid the design and operation strategy of isolation facilities. In this work, the interzonal migration of airborne infectious particles by human movement was studied experimentally in an isolation ward. Artificial saliva solution with benign E. coli bacteria was aerosolized to simulate bacterium-laden infectious particles. The interzonal migration of aerosolized bacteria was characterized by biological air sampling. Less than 1% of airborne infectious particles were transported to the higher pressure zone when door was closed. With human movement, 2.7% of the particles were transported from the anteroom to the corridor. From high-to-low pressure zones, as much as 20.7% of airborne infectious particles were migrated. Only a minimal amount of particles was transported from the corridor to the positive pressure nurses' station. Infection risk of tuberculosis of the healthcare workers and other occupants in the isolation wards were also assessed based on the measured migration ratios.

PRACTICAL IMPLICATIONS

Human movement is an important factor governing interzonal migration. It is the main cause of migration of airborne infectious particles to a relatively negative pressure zone. This study provides a set of experimentally obtained particle migration ratios by human movement. Other than serving as empirical data for further studies on the mechanics, these migration ratios can also be used to assess the infection risk for occupants in the isolation ward.

Hospital ventilation simulation for the study of potential exposure to contaminants

Airflow and ventilation are particularly important in healthcare rooms for controlling thermo-hygrometric conditions, providing anaesthetic gas removal, diluting airborne bacterial contamination and minimizing bacteria transfer airborne. An actual hospitalization room was the investigate case study. Transient simulations with computational fluid dynamics (CFD), based on the finite element method (FEM) were performed to investigate the efficiency of the existing heating, ventilation and air-conditioning (HVAC) plant with a variable air volume (VAV) primary air system. Solid modelling of the room, taking into account thermo-physical properties of building materials, architectural features (e.g., window and wall orientation) and furnishing (e.g., beds, tables and lamps) arrangement of the room, inlet turbulence high induction air diffuser, the return air diffusers and two patients lying on two parallel beds was carried out. Multiphysics modelling was used: a thermo-fluidynamic model (convection-conduction and incompressible Navier-Stokes) was combined with a convection-diffusion model. Three 3D models were elaborated considering different conditions/events of the patients (i.e., the first was considered coughing and/or the second breathing). A particle tracing and diffusion model, connected to cough events, was developed to simulate the dispersal of bacteria-carrying droplets in the isolation room equipped with the existing ventilation system. An analysis of the region of droplet fallout and the dilution time of bacteria diffusion of coughed gas in the isolation room was performed. The analysis of transient simulation results concerning particle path and distance, and then particle tracing combined with their concentration, provided evidence of the formation of zones that should be checked by microclimatic and contaminant control. The present study highlights the fact that the CFD-FEM application is useful for understanding the efficiency, adequacy and reliability of the ventilation system, but also provides important suggestions for controlling air quality, patients' comfort and energy consumption in a hospital.

CFD simulation of airborne pathogen transport due to human activities

Computational Fluid Dynamics (CFD) is an increasingly popular tool for studying the impact of design interventions on the transport of infectious microorganisms. While much of the focus is on respiratory infections, there is substantial evidence that certain pathogens, such as those which colonise the skin, can be released into, and transported through the air through routine activities. In these situations the bacteria is released over a volume of space, with different intensities and locations varying in time rather than being released at a single point. This paper considers the application of CFD modelling to the evaluation of risk from this type of bioaerosol generation. An experimental validation study provides a direct comparison between CFD simulations and bioaerosol distribution, showing that passive scalar and particle tracking approaches are both appropriate for small particle bioaerosols. The study introduces a zonal source, which aims to represent the time averaged release of bacteria from an activity within a zone around the entire location the release takes place. This approach is shown to perform well when validated numerically though comparison with the time averaged dispersion patterns from a transient source. However, the ability of a point source to represent such dispersion is dependent on airflow regime. The applicability of the model is demonstrated using a simulation of an isolation room representing the release of bacteria from bedmaking.

Role of two-way airflow owing to temperature difference in severe acute respiratory syndrome transmission: revisiting the largest nosocomial severe acute respiratory syndrome outbreak in Hong Kong

By revisiting the air distribution and bioaerosol dispersion in Ward 8A where the largest nosocomial severe acute respiratory syndrome (SARS) outbreak occurred in Hong Kong in 2003, we found an interesting phenomenon. Although all the cubicles were in 'positive pressure' towards the corridor, the virus-containing bioaerosols generated from the index patient's cubicle were still transmitted to other cubicles, which cannot be explained in a traditional manner. A multi-zone model combining the two-way airflow effect was used to analyse this phenomenon. The multi-zone airflow model was evaluated by our experimental data. Comparing with the previous computational fluid dynamic simulation results, we found that the air exchange owing to the small temperature differences between cubicles played a major role in SARS transmission. Additionally, the validated multi-zone model combining the two-way airflow effect could simulate the pollutant transport with reasonable accuracy but much less computational time. A probable improvement in general ward design was also proposed.

Optofluidic device monitoring and fluid dynamics simulation for the spread of viral pathogens in a livestock environment

Rapid monitoring of the spreads of porcine reproductive and respiratory syndrome virus (PRRSV) was attempted using samples collected from nasal swabs of pigs and air samplers within an experimental swine building. An optofluidic device containing liquid-core waveguides was used to detect forward Mie light scattering caused by the agglutination of anti-PRRSV-conjugated submicron particles, with enhanced sensitivity, signal reproducibility, and reusability (reusable up to 75 assays). These results were compared with reverse transcription polymerase chain reaction (RT-PCR) assays (35 cycles) and showed excellent agreements to them. Each assay took less than 10 min including all necessary sample pre-processing, while the RT-PCR assays took up to 4 h including sample pre-processing and gel imaging for PCR products. A 3-D computational fluid dynamics (CFD) simulation was utilized to track the transport and distribution of PRRSV (from the mouths of pigs to the exhaust fans) within a swine building, and compared with the readings from an optofluidic device. Simulation results corresponded well with the experimental data, validating our 3-D CFD model for the spread of viral pathogens in a livestock environment. The developed optofluidic device and 3-D CFD model can serve as a good model for monitoring the spread of influenza A (swine and avian) within animal and human environments.

Removal of exhaled particles by ventilation and deposition in a multibed airborne infection isolation room

Removal of airborne particles in airborne infection isolation rooms is important for infection control of airborne diseases. Previous studies showed that the downward ventilation recommended by Centers for Disease Control and Prevention (CDC) could not produce the expected 'laminar' flow for pushing down respiratory gaseous contaminants and removing them via floor-level exhausts. Instead, upper-level exhausts were more efficient in removing gaseous contaminants because of upward body plumes. The conventional wisdom in the current CDC-recommended design is that floor-level exhausts may efficiently remove large droplets/particles, but such a hypothesis has not been proven. We investigated the fate of respiratory particles in a full-scale six-bed isolation room with exhausts at different locations by both experimental and computational studies. Breathing thermal manikins were used to simulate patients, and both gaseous and large particles were used to simulate the expelled fine droplet nuclei and large droplets. Gaseous and fine particles were found to be removed more efficiently by ceiling-level exhausts than by floor-level exhausts. Large particles were mainly removed by deposition rather than by ventilation. Our results show that the existing isolation room ventilation design is not effective in removing both fine and large respiratory particles. An improved ventilation design is hence recommended.

PRACTICAL IMPLICATIONS

Our findings of the relatively poor performance of fine-particle removal by the existing CDC design of isolation room ventilation suggests a need for improvement, and the findings of the removal of large particles by deposition, not by ventilation, suggest that floor-level exhausts are unnecessary, and that regular surface cleaning and disinfection is necessary, thus providing evidence for maintaining isolation room surface hygiene.

The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

Dental healthcare workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients' mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of airflow, energy and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the airflow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs' exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and the DHCW are important considerations for reducing DHCWs' exposure to droplets/aerosol particles emitted from the patient's mouth during treatments.

Numerical study on the dispersion of airborne contaminants from an isolation room in the case of door opening

A negative pressure isolation room is built to accommodate and cure patients with highly infectious diseases. An absolutely airtight space effectively prevents infectious diseases from leaking out of the isolation room. Opening the door leads to a breakdown in isolation conditions and causes the dispersion of infectious air out of the isolation room. Extensively employed to manage smoke in cases of fires at subway and highway tunnels, a concept of controlling airflow is applied to the study. This study proposes a design of ventilation system to control air flow rate for containing airborne contaminant and preventing its spread to the adjacent rooms when the door to the isolation room is opened and closed. This paper employs computational fluid dynamics (CFD) as a more effective approach to examine the concentration maps of airborne contaminants and the airflow patterns of room air and discuss the influence of temperature differences between two rooms on airborne dispersion. Results show that an air velocity above 0.2 m/s via a doorway effectively prevents the spread of airborne contaminants out of the isolation room in the state of door opening.

Exhaled air and aerosolized droplet dispersion during application of a jet nebulizer

BACKGROUND

As part of our influenza pandemic preparedness, we studied the dispersion distances of exhaled air and aerosolized droplets during application of a jet nebulizer to a human patient simulator (HPS) programmed at normal lung condition and different severities of lung injury.

METHODS

The experiments were conducted in a hospital isolation room with a pressure of - 5 Pa. Airflow was marked with intrapulmonary smoke. The jet nebulizer was driven by air at a constant flow rate of 6 L/min, with the mask reservoir filled with sterile water and attached to the HPS via a nebulizer mask. The exhaled leakage jet plume was revealed by a laser light sheet and images captured by high-definition video. Smoke concentration in the plume was estimated from the light scattered by smoke and droplet particles.

FINDINGS

The maximum dispersion distance of smoke particles through the nebulizer side vent was 0.45 m lateral to the HPS at normal lung condition (oxygen consumption, 200 mL/min; lung compliance, 70 mL/cm H(2)O), but it increased to 0.54 m in mild lung injury (oxygen consumption, 300 mL/min; lung compliance, 35 mL/cm H(2)O), and beyond 0.8 m in severe lung injury (oxygen consumption, 500 mL/min; lung compliance, 10 mL/cm H(2)O). More extensive leakage through the side vents of the nebulizer mask was noted with more severe lung injury.

INTERPRETATION

Health-care workers should take extra protective precaution within at least 0.8 m from patients with febrile respiratory illness of unknown etiology receiving treatment via a jet nebulizer even in an isolation room with negative pressure.

Airflow and droplet spreading around oxygen masks: a simulation model for infection control research

Background

Respiratory assist devices, such as oxygen masks, may enhance the potential to spread infectious aerosols from patients with respiratory infections.

Methods

A technique was developed to visualize exhaled aerosols during simulated patients' use of oxygen masks in a health care setting and tested using the simple, the nonrebreathing, and the Venturi oxygen masks. A smoke tracer was introduced into one of the lungs of the model to enable it to mix with the incoming oxygen and then to be further inhaled/exhaled by the model according to a variety of realistic respiratory settings (14, 24, and 30 breaths per minute, with tidal volumes of 500, 330, 235 mL, respectively) and oxygen supply flow rates (between 6 and 15 liters per minute). Digital recordings of these exhaled airflow patterns allowed approximate distances to be estimated for the extent of the visible exhaled air plumes emitted from each oxygen mask type at these settings.

Results

It was found that the simple, the nonrebreathing, and the Venturi-type oxygen masks produced exhaled smoke plumes over minimum distances of 0.08 to 0.21 m, 0.23 to 0.36 m, and 0.26 to 0.40 m, respectively.

Conclusion

Health care workers may therefore consider any area within at least 0.4 m of a patient using such oxygen masks to be a potential nosocomial hazard zone.

Hospital and community acquired infection and the built environment--design and testing of infection control rooms

Negative-pressure isolation rooms are required to house patients infected with agents transmissible by the aerosol route in order to minimise exposure of healthcare workers and other patients. Housing patients in a separate room provides a barrier which minimises any physical contact with other patients. An isolation room held at negative pressure to reduce aerosol escape and a high air-change rate to allow rapid removal of aerosols can eliminate transmission of infectious aerosols to those outside the room. However, badly designed and/or incorrectly operating isolation rooms have been shown to place healthcare workers and other patients at risk from airborne diseases such as tuberculosis. Few standards are available for the design of isolation rooms and no pressure differential or air-change rates are specified. Techniques such as aerosol particle tracer sampling and computational fluid dynamics can be applied to study the performance of negative-pressure rooms and to assess how design variables can affect their performance. This should allow cost-effective designs for isolation rooms to be developed. Healthcare staff should be trained to understand how these rooms operate and there should be systems in place to ensure they are functioning correctly.

Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises

The epidemics of severe acute respiratory syndrome (SARS) in 2003 highlighted both short- and long-range transmission routes, i.e. between infected patients and healthcare workers, and between distant locations. With other infections such as tuberculosis, measles and chickenpox, the concept of aerosol transmission is so well accepted that isolation of such patients is the norm. With current concerns about a possible approaching influenza pandemic, the control of transmission via infectious air has become more important. Therefore, the aim of this review is to describe the factors involved in: (1) the generation of an infectious aerosol, (2) the transmission of infectious droplets or droplet nuclei from this aerosol, and (3) the potential for inhalation of such droplets or droplet nuclei by a susceptible host. On this basis, recommendations are made to improve the control of aerosol-transmitted infections in hospitals as well as in the design and construction of future isolation facilities.