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Head orientations directly determine movement directions of exhaled pathogen-laden droplets, while there is a lack of research about the effect of the infected person's head orientations on respiratory disease transmission during close contact. This work experimentally investigated the effect of different head orientations of an infected person (IP) on the bioaerosol deposition on a healthy person (HP) during close contact. Also, the effectiveness of PV flow in reducing bioaerosol deposition on the HP under the IP’s different head orientations was investigated. Bacteriophage T3 was employed to represent viruses inside the cough-generated aerosols. The bioaerosol depositions on different locations of the HP’s upper body (chest, shoulder, and neck) and face (chin, mucous membranes, cheek, and forehead) were characterized by a cultivation method. Results showed that the IP’s different head orientations resulted in significantly different deposition density on the HP. PV flow could reduce the bioaerosol deposition remarkably for most cases investigated. The effectiveness of PV flow in reducing deposition on the HP was significantly affected by the IP’s head orientations. Findings suggest that changing head orientations can be a control measure to reduce the bioaerosol deposition. Personalized ventilation can be a potential method to reduce the bioaerosol deposition on the HP. © 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Respiratory bioaerosol deposition in public transport cabins is critical for risk analysis and control of contact transmission. In this work, we built a two-row four-seat setup and an air duct system to simulate a cabin environment. A thermal manikin on the rear left-hand seat was taken as the infected passenger (IP) and “coughed” three times through a cough generator. The deposited viruses and droplets on nearby seats were measured by a cultivation method and microscope, respectively. The effects of seat backrest and overhead gasper jet were studied. Results showed that the number of deposited virus on the front seat was one order of magnitude higher than that on other seats which only contained droplets smaller than 10 µm in diameter. When the backrest was 15 cm higher than the cough, the deposited number of viruses was reduced to 5% of that with the backrest at the same height with the cough. The gasper jet above the IP with a velocity of 1.5 m/s can reduce the deposited viruses to 4% of that with gasper off. It indicates that both the gasper jet and backrest can work as mitigation measures to block the cough jet and protect the nearby passengers. © 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

A short distance between infected persons and exposed persons can probably result in a high risk of respiratory infection. This work experimentally investigated the short-range bioaerosol deposition and inhalation by a healthy person (HP) and the effect of a personalized ventilation (PV) on the HP, who was exposed to cough droplets from an infected person (IP) over a short distance between 0.5 m and 1.2 m. Benign E. coli was employed to represent the pathogen from the respiratory droplets. The microorganism deposition on different locations of the HP’s body (shoulder, chest and body back) and face (forehead, cheek, and chin) as well as inhalation were characterized by a cultivation method. It was found that the inhalation and deposition of vital pathogens on the face and body surface of the HP increased as the distance between the HP and the IP decreased. PV has been showed to reduce exposure by inhalation, while this is the first time to demonstrate that PV can also significantly reduce the number deposition. By optimizing the velocity of PV flow with respect to the distance, the bioaerosol deposited on the face and body and inhaled could be reduced by a maximum of 98%, 85% and 100%, respectively. For short-range disease transmission, physical barriers, e.g., mask and partition, are the conventional and believed to be the only intervention measures. The current results indicate that PV can be a potential method for infection control in the area of disease transmission in close contact situations. Copyright © 2021 American Association for Aerosol Research. © 2021 American Association for Aerosol Research.

Head orientations directly determine movement directions of exhaled pathogen-laden droplets, while there is a lack of research about the effect of the infected person's head orientations on respiratory disease transmission during close contact. This work experimentally investigated the effect of different head orientations of an infected person (IP) on the bioaerosol deposition on a healthy person (HP) during close contact. Also, the effectiveness of PV flow in reducing bioaerosol deposition on the HP under the IP’s different head orientations was investigated. Bacteriophage T3 was employed to represent viruses inside the cough-generated aerosols. The bioaerosol depositions on different locations of the HP’s upper body (chest, shoulder, and neck) and face (chin, mucous membranes, cheek, and forehead) were characterized by a cultivation method. Results showed that the IP’s different head orientations resulted in significantly different deposition density on the HP. PV flow could reduce the bioaerosol deposition remarkably for most cases investigated. The effectiveness of PV flow in reducing deposition on the HP was significantly affected by the IP’s head orientations. Findings suggest that changing head orientations can be a control measure to reduce the bioaerosol deposition. Personalized ventilation can be a potential method to reduce the bioaerosol deposition on the HP. © 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Knowledge of respiratory bacteria/virus concentration and distribution on a surface is critical for assessing contact transmission. Here, we investigate the direct bioaerosol deposition and distribution on a near surface from a cough experimentally. A cough generator is used to release bacterium/virus-laden droplets. A solid surface is put in front of the cough generator. Escherichia coli (E-coli) and bacteriophage are used to represent the respiratory bacteria and virus, respectively. Results show that the number concentration of deposited droplets and viable bacteria/viruses on the surface decrease from the impingement point to surface edge. We identify the region of the impingement area on the surface in which the microorganism fraction accounts for around 83% of the overall deposited bacteria/phage along a vertical line. The E. coli-laden droplets have similar distribution with that of the phage-laden droplets, meaning that the microorganisms inside the droplets do not affect the droplet deposition onto near surfaces.

Bioaerosol deposition, distribution, and detachment behavior on near surfaces from a cough is important for risk assessment and control of the contact route of respiratory disease transmission, such as SARS, H1N1, seasonal influenza, and Covid-19. A custom-built cough generator was used to simulate a real cough. Escherichia coli (E-coli) and bacteriophage were used to represent the common respiratory bacteria and viruses, respectively. Firstly, bioaerosol deposition and distribution on front flat surfaces were studied. The cough jet impinges on the front surface and then forms a parallel spreading flow above the surface. The distributions of viable bacteria/viruses follow the skew normal equation. Survivability of bacterium/virus during the cough and deposition processes is almost uniform on near surfaces. Secondly, bioaerosol deposition and distribution on nearby seats in a cabin environment were studied, which is a common enclosed environment to cause respiratory disease transmission. The viable virus on front seat is one order of magnitude higher than that on the other near seats because of the large droplets on front seat. Increasing the height of the backrests or opening the air jet for the infector could reduce the virus deposited on front seat to less than 10%. Thirdly, the detachment behavior of deposited droplets from a solid surface was studied. The droplet detaches totally from a surface under a lateral force, while it detaches partially under a normal force, leaving a smaller droplet on surface. The adhesion of a droplet to a rough surface depends on the liquid film left on surface after droplet detachment. The surface energy analysis integrating the left liquid film has a good linear relationship with the experimental adhesion. The bioaerosol deposition, distribution, and detachment dynamics on near surfaces from a cough help understand the contact route and setup the engineering control of respiratory disease transmission.

Understanding of the droplet detachment behavior from rough hydrophilic surfaces is important in many biological and industrial applications such as biomedicine, surface coating, and pathogen-laden aerosol resuspension. Due to the partial detachment of the droplet on hydrophilic surfaces, leaving behind some droplet residues, the adhesion behavior is extremely complicated. Here we reveal a new adhesion mechanism between a droplet and a rough hydrophilic surface. The adhesion behavior is controlled by a liquid film stuck in the surface microstructure. We establish a model to describe the contributions of liquid film and naked solid peaks, to the work of adhesion and verify the model experimentally. We also find that the normal adhesion force is about 3.35 ± 0.25 times of the lateral adhesion force for different surface roughness, meaning that the separation direction is an important factor affecting adhesion due to the different separation mechanisms. The results of this work shed new insights on the understanding of droplet detachment and adhesion to a rough surface. © 2019 Elsevier Ltd

Resuspension of droplets from surfaces is an important indoor phenomenon. If the droplets are infectious, they would become a new source of airborne disease transmission. Since different kinds of materials that have different surface roughness are used in an indoor environment, investigation of the effect of surface roughness on droplet resuspension behavior is essential. Experiments were carried out by using a centrifuge. Unlike solid particles which detach as a whole, droplets detach by portion when they are under an increasing force field. The adhesive force between droplets and surfaces is found to be proportional to the contact diameter, and the adhesion coefficient is dependent on the roughness. Different from solid particles, the larger the roughness, the harder it is for droplets to be resuspended. This work reveals how roughness affects droplet resuspension and how droplet resuspension behavior differs from that of solid particles. This will be useful for risk assessment on disease transmission. © 2018 15th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2018. All rights reserved.