The function of aerosols in transmitting and infecting of respiratory infectious diseases and its risk prediction
TL;DR: In this paper, the authors used the Wells-Riley equation and its revised models to predict cross-infection risk and clarified the important role of ventilation rate on reducing risk of airborne infection.
Abstract: The significance of respiratory infectious diseases has been iterated by outbreaks of severe acute respiratory syndromes (SARS), influenza A (H1N1), Middle East Respiratory Syndrome (MERS), etc. in recent decades. Those outbreaks of infectious diseases mostly occur in indoor environment. The exhaled droplets and droplet nuclei, the residues of droplets, from the infector are considered as the main transmitted vehicles of respiratory infectious diseases. When the infectors are breathing, speaking, coughing, sneezing, etc., they will exhale droplets with different numbers, sizes and speeds. Large droplets will deposit on floor quickly due to gravity, while small droplets will evaporate in seconds. The droplets spreading distance varies with temperature, humidity and air distribution systems. The distance is usually less than 2 m. Some studies also find that there exists a threshold distance of droplet nuclei spreading, where droplet nuclei concentration decreases quickly, indicating that short distance airborne infection risk is much higher than long distance airborne infectious diseases. The viability of microorganism in droplets is related to temperature, relative humidity, sensation of oxygen, exposure in ultraviolet, etc. The death rate of microorganism in droplets is much higher at beginning seconds due to evaporation, iterating the higher risk of short-range infection. Some studies also show that the pathogens survived well in low RH or high RH, which indicates the significance of controlling RH in indoor environment not only for thermal comfort but also for risk control. Wells-Riley equation is introduced here, which is developed by Riley and formulated on following assumptions: the infectious diseases are transmitted via droplet nuclei only; the distribution of droplet nuclei in the room is uniform; the death rate of pathogens is ignored. Wells-Riley equation and its revised models have been used to predict cross-infection risk and have clarified the important role of ventilation rate on reducing risk of airborne infection. However, the models for estimating risk of respiratory infectious diseases almost based on statistical methods. It needs to be improved to evaluate the role of close range, droplet-borne and short-range airborne infection risk. Some methods to cut off short-range airborne routes are also introduced. With the improved understanding of the spread, movement and evaporation of human exhaled droplets in different indoor environment, the understandings of transmission routes of respiratory infectious diseases deepen. However, these understandings have not been well integrated with the risk prediction model to predict and evaluate the infection risk of respiratory infectious diseases. There is a need to combine the model for predicting dispersion of droplets with the viability and pathogenicity of microbes, which can help human evaluate risk and take proper public means to reduce the cross-infection. According to the current understanding of transmission route of respiratory infectious diseases, in addition to reducing the contact probability by surface disinfection, the ventilation methods can be applied to reduce cross-infection. It is suggested to cut off the spread of droplet borne and short-range airborne, of which infection risk is much higher than that of long range airborne. Improving the effective ventilation rate can reduce the risk of long-range airborne. Airflow direction between rooms can be controlled by pressurization to prevent cross-infection between rooms. To control respiratory infectious diseases efficiently, it needs cooperation of engineering, medical, fluid mechanics, public health, environment and other disciplines. After the outbreak of SARS in 2003, much progress has been made. However, due to incubation, instantaneous, biological diversity of respiratory infectious diseases, it is extremely difficult to do fine quantitative study. A variety of infection control measures and methods are mainly based on experience. Many scientific problems, such as the mechanism of infection and the method of prediction, need further studies in multi disciplines.
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TL;DR: A modified Wells-Riley model combining the airborne route and close contact route was proposed to predict the infection risks of coronavirus disease 2019 (COVID-19) in main functional spaces of an outpatient building in Shenzhen, China.
Abstract: A modified Wells-Riley model combining the airborne route and close contact route was proposed to predict the infection risks of coronavirus disease 2019 (COVID-19) in main functional spaces of an outpatient building in Shenzhen, China. The personnel densities and ventilation rates in the 20 waiting rooms, outpatient hall and hospital street were on-site measured. The average fresh air volume per person and occupant area per person in the 20 waiting rooms were 77.6 m 3/h and 6.47 m2/per, satisfied with the Chinese standard. The average waiting time of the occupants was 0.69 h. Thus, assuming the proportion of infected people in the outpatient building was 2%, the daily average infection probabilities of COVID-19 in the 20 waiting rooms were 0.19–1.88% with a reasonable setting of the quanta produced by an infector (q = 45 quanta/h) and the effective exposure dose of pathogen per unit close contact time (β = 0.05 h−1 ). The design of the semi-closed hospital street with a height of 24 m improved its natural ventilation with a fresh air volume per person of 70–185 m 3/h and further dilute the viral aerosol and decreased the infection risk to a negligible level (i.e., below 0.04% with an infector proportion of 2%). The assessment method provides real-time prediction of indoor infection risk and good assist in spread control of COVID-19.
31 citations
TL;DR: A circulated air curtain composed of end-to-end plane jets generated by a relay of air pillars is proposed to confine exhaled contaminants in this study and results can provide a reference for the subsequent design and improvement in applying air curtain in hospital wards or other places.
Abstract: Air curtain is an efficient device for cutting off airflow and confining contaminants. Inspired by the ability, a circulated air curtain composed of end-to-end plane jets generated by a relay of air pillars is proposed to confine exhaled contaminants in this study. Furthermore, the optimization study of computational fluid dynamics (CFD) is conducted to explore cutting-off performance and find better design parameters under different conditions, i.e., human-curtain distance, enclosure shape, jet velocity from air pillar, and exhalation modes. The multidirectional blockage and vortex-like rotative transmission routes of exhaled airflow are observed when air curtain exists. Results indicate that contaminants are concentrated around the source. The average mole fraction of exhaled contaminants outside air curtain under different human-curtain distance decreases 4.3%–19.6% compared to mixing ventilation with same flux. Shortening the human-curtain distance can improve the performance of air curtain and may change the direction of exhaled airflow. Moreover, It has better performance when the enclosure shape is close to a circle. Higher jet velocity is better for improving the confinement performance, but the trend is not very obvious as velocity increases. For exhalation modes, it is more challenging to control exhaled contaminants for intense exhalation activity (such as coughing) in steady simulation, but results in transient simulation show better performance when coughing only once. These results can provide a reference for the subsequent design and improvement in applying air curtain in hospital wards or other places, especially during the period of flu outbreak.
23 citations
TL;DR: In this paper, the authors quantitatively estimate the SARS-CoV-2 transmission probability and evaluate the influence of environmental parameters and individual intervention on the epidemic prevention, and employ the reproductive number R to quantify diverse mitigation strategies.
Abstract: Public transport is a fundamental service for the resumption of work and production, but the enclosed environment and dense population create very favorable conditions for the spread of epidemic infections. Thus, effective public health interventions are urgently introduced. The objective of this paper is to quantitatively estimate the SARS-CoV-2 transmission probability and evaluate the influence of environmental parameters and individual intervention on the epidemic prevention. For this purpose, (1) we estimate the virus emission rate with Diamond Princess Cruise Ship infection data by Monte Carlo simulation and the improved Wells-Riley model, and (2) employ the reproductive number R to quantify diverse mitigation strategies. Different determinants are examined such as the duration of exposure, the number of passengers combined with individual interventions such as mask type and mask-wearing rate. The results show that the SARS-CoV-2 quantum generation rate is 185.63. The R shows a stronger positive correlation with the exposure time comparing to the number of passengers. In this light, reducing the frequency of long-distance journeys on crowded public transportation may be required to reduce the spread of the virus during the pandemic. N95 mask and surgical mask can reduce the transmission risk by 97 and 84%, respectively, and even homemade mask can reduce the risk by 67%, which indicates that it is necessary to advocate wearing masks on public transportation.
12 citations
TL;DR: Wang et al. as mentioned in this paper defined the air flow field area based on on-site wind environment measurements, crowd behavior annotation, and CFD simulation, which can be used as a guideline for future residential planning and design from the perspective of preventing airborne diseases.
Abstract: The wind environment in residential areas can exert a direct or indirect influence on the spread of epidemics, with some scholars paying particular attention to the epidemic prevention and control of residential areas from the perspective of wind environments. As a result, it is urgent to re-examine the epidemic prevention response of residential spaces. Taking high-rise residential areas in Xi’an as an example, the article defines the air flow field area based on on-site wind environment measurements, crowd behavior annotation, and CFD simulation. Using the double-effect superposition of crowd behavior and risk space, the paper undertook a multiple identification strategy of epidemic prevention space. The identification methods and management and control strategies of epidemic prevention in high-rise residential areas are proposed. Additionally, the living environment of residential areas is optimized, and a healthy residential space is created. The transformation from concept and calls for action to space implementation is made to provide a reference for improving the space management and control capabilities in high-rise residential areas in China. The results of this study can be used as a guideline for future residential planning and design from the perspective of preventing airborne diseases.
09 Feb 2022
TL;DR: In this article , the authors established a full-scale car model with full load conditions based on the theory of computational fluid dynamics and analyzed the air quality in the passenger compartment of a high-speed train.
Abstract:
A high-speed train has a large passenger volume and long running time. The optimized design of the ventilation system is of great importance to improve the car comfort and air quality in the passenger compartment. Therefore, this study establishes a full-scale car model with full load conditions based on the theory of computational fluid dynamics. The middle air supply at the top of the passenger compartment was considered as an example, the flow field structure and respiratory pollutants diffusion characteristics in the passenger compartment under the exhaust air at both ends, lower and upper exhausts, upper exhaust mode that changes the ratio of the exhaust flow on both sides were compared and analyzed. The nonuniformity coefficient, energy utilization coefficient, and ventilation efficiency indicators are used for evaluation and analysis. The results show that when the improved upper exhaust method is adopted, the comprehensive evaluation index in the passenger compartment is the best; the average indoor concentration is less than