Online & Oslo, Norway
21-23 June 2021
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Session 10: Airborne transmission of infectious diseases
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10:30am - 10:42am
Transport of Contaminated Agents in Hospital Wards - Exposure Control with a Personalized Healthcare Ventilation System: Numerical Study
1KTH Royal Institute of Technology, Sweden; 2Chalmers University of Technology, Sweden
Contaminated agents in hospital wards are the source of nosocomial infections known as hospital-acquired infection (HAI) or healthcare-associated infections (HAIs). The spread of infection is closely associated with indoor airflow patterns created by room ventilation. Ventilation plays an essential role in minimizing the transport of airborne infectious diseases such as Covid-19 and SARS in the hospital ward. The goal of this study is to find efficient elimination technology for better control of contaminated agents. This work aims to study the influence of using local air supply and exhaust on the distribution and removal of airborne particles. Previous studies are compared to determine the factors that influence the environment and contaminants concentration in hospitals, along with infection control information. Numerical analyses of ventilation performance were conducted in a typical hospital ward. This study demonstrates factors that critically affect indoor bacteria-carrying particles conditions in the air. This research also provides a valuable reference to minimize indoor contamination levels with a personalized healthcare ventilation system in the future. Computational Fluid Dynamics technique was used to model the airflow field and contamination distribution in the ward environment. Simulated results of the transmission and removal of airborne infectious particles using local air supply and exhaust showed that the bacterium spread from a patient confined to his bed was limited and for certain conditions significantly eliminated. Consequently, the higher efficiency of particle removal and moderating the transmission of contaminated agents was obtained by using locally implemented air supply diffusers and exhaust grills. Thus, this strategy can shorten the contaminated agent’s exposure time for both patient and healthcare staff, as a result, reduction in cross-infection at the hospital.
10:42am - 10:54am
Experimental investigation of the spread of airborne CFU in an research-OR under different air flow regimes using tracer particles
Technische Universität Berlin, Germany
Regarding the risk of surgical site infections (SSI), surgical operations take place in protected environments. SSI can be caused by endogenious germs, smear infections or by airborne colony forming units (CFU) that sediment in the wound or on surgical instruments.
Aim of this experimental study is to design an aerosol generator that produces airborne particles with the aerodynamic properties of airborne colony-forming units (CFUs) occurring in operating rooms (ORs). Those tracer particles are produced by dispersing a suspension of tracer particles with a size range of 2 to 20 µm using a collision nebulizer. The essential properties were investigated by a literature research. Furthermore, the classified source strength and corresponding measurement uncertainty of the aerosol generator were measured using a test stand with an optical particle counter in a cleanroom environment.
It could be shown that the aerosol generators designed produce particles in the relevant size classes of the airborne germs emitted by OR personnel.
The aerosol generators disperse particles with the size of the airborne CFU occurring in real OR, usually between 2 and 12 µm, into the indoor air, in order to be able to make representative statements on the removal of germs considering the aerodynamic properties of particles.
10:54am - 10:59am
COVID-19 dent guard and movable room for dentists' practice with design solution for air cleaning in natural ventilation.
Bangkok university, Thailand
Virus could dependently spread in the air rising human infection. The global awareness issue by COVID-19 of virus movement is average size about 0.125 µm smaller than dust leaded to lung disorder. Thus, the new normal lifestyle with social distancing between human is recommended for minimum 2 meters to lessen droplets infection. Therefore, dentist job is a most risk of unavoidable to contact in respiration area with their patient. A risk of infection for both patient and dentist is high at position of mouth. Thus, a dent guard is prompt designed for reduce water spreading with clear non-reflected plastic shield. Furthermore, a plastic covered-moveable room has been distributed over hospital and healthcare. The outright dent guard is created for temporary solution required to be analyzed its effectiveness for human health protection. A monitoring particle spreading are two solutions for dent guard and moveable room with computational fluid dynamics (CFD) simulation on virus dilution and accumulation in room. The demonstration of air cleaning distribution is a dental guard size 0.50 m. × 0.60 m. with two openings of 0.25 m. diameters for dentist operation. Dental services sensitively prohibit for tooth scaling due to risk of virus diffusion in air. The device of tooth scaling is a source to model air diffusion at general frequency 30 KHz. The virus is performed as a particle flow in building by CFD calculation and monitored in shape of dent guard. The results found summaries on capable dent guard and moveable room for virus dilution in air. This can be a design solution for this crisis.
10:59am - 11:11am
Ventilation strategies to minimise the airborne virus transmission in indoor environments
1Department of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, via G. Di Biasio, 43, 03043 Cassino (FR), Italy; 2Department of Civil Engineering, Environmental Engineering and Architecture, University of Cagliari; 3International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Australia
SARS-CoV-2 pandemic highlighted the importance of healthy buildings and proper ventilation in indoor environments. As recently highlighted by the scientific community, the airborne transmission route of the virus suggests that adopting containment measures just relying upon a safe distance (i.e. 1 m as “droplet distance”) cannot reduce the transmission by air in indoor environments whereas a key role in lowering the probability of infection indoors (and, then, limiting the spread of the pandemic) is given to ventilation.
In light of this, indoor environments with high occupancy can be hotspots for pandemic diffusion; indeed, the school environments turned in the spotlight as the governments worldwide were in the uncomfortable role of prioritising the right to education or health.
The present paper aims at determining the probability of infection of people exposed to SARS-CoV-2 and Seasonal Influenza Viruses due to the airborne transmission route in schools under different ventilation, emission, and mitigation scenarios and discussing how to operate the ventilation systems in view of a minimisation of the transmission.
A recently developed approach, able to quantify the probability of infection due to exposure in an environment in the presence of an infected subject, was adopted. The approach is articulated in four steps: (i) evaluation of the virus emission (based on a model recently proposed by the authors); (ii) assessment of the exposure to quanta concentration in the microenvironment (through a box-model method); (iii) evaluation of the dose of quanta received by an exposed susceptible subject; and (iv) estimation of the probability of infection based on a proper dose-response model.
In the presented study, different emission modes (e.g. teacher emitting while taking lesson, students breathing or talking while attending the lesson), ventilation methods (e.g. manual airing, mechanical ventilation) and mitigation solutions (e.g. wearing a facemask, using purifiers, using microphones) were taken into account. Furthermore, the probability of infection and the maximum classroom occupancy to guarantee a reproduction number lower than one were evaluated. Moreover, the adoption of students’ exhaled CO2 as a proxy of the virus infection risk was demonstrated and discussed. The findings of the study provide a viable method to reopen schools safely and mitigate the spread of the pandemic, even considering the virus airborne transmission route.
11:11am - 11:23am
A Practical and Efficient Testing Method for Indoor Airborne Pathogens
1Aerosol Devices Inc, Fort Collins, CO, USA; 2MRS Consulting, Minneapolis, MN USA; 3University of Colorado at Boulder, USA
The COVID-19 pandemic has been a global scourge, killing over 2M people in its first year. As devastating as this pandemic has been, it will not be the last; other novel pathogens will undoubtedly emerge. Like SARS-CoV-2, some will be highly transmissible as aerosols. Even the less-feared seasonal influenza kills hundreds of thousands of people every year, and tuberculosis kills about the same number of people as COVID-19 – about 1.5-2M each year. All of these diseases are transmitted primarily via infectious airborne viruses and bacteria. Instruments capable of rapidly detecting these airborne pathogens will help limit human exposure and mitigate disease transmission.
Here we describe a new approach to sampling bioaerosols using condensation growth tube (CGT) capture. The CGT’s cold-hot temperature zones create water vapor supersaturation forcing condensation onto particles to form droplets. These droplets are gently collected keeping viruses, bacteria and fungal spores intact. The unique advantages of the CGT are: (1) high collection efficiency (>95% of particles from <10 nm to 10 µm), (2) instant genomic preservation of DNA/RNA upon capture, and (3) concentrated sample collection compatible with standard genomic analyses such as RT-qPCR and DNA/RNA sequencing. The work flow for sample analysis is identical to that used in diagnostic testing of nasal swabs.
In response to the need for broader access to effective bioaerosol samplers, we have developed the new BioSpot-GEM™ sampler, which is affordable, compact and quiet. These features as well as automated sample timing and simple operation make it well-suited for bio-surveillance in hospitals, dental offices, nursing homes, schools, and transportation centers by indoor air quality professionals as well as bioaerosol researchers. We used finite element analysis to model flow, heat/mass transfer and condensation-driven droplet growth to optimize the design of the sampler. Our model determines where condensation of supersaturated vapor begins along a particle’s trajectory and then calculates the subsequent droplet growth, accounting for the Kelvin effect on the equilibrium vapor pressure over a curved surface and non-continuum regime transport of both vapor and latent heat from the droplet. We experimentally validated the collection efficiency predicted by our model and demonstrated recovery of viral RNA from samples collected using the GEM sampler compared to a multiple orifice uniform deposit impactor (MOUDI).
11:23am - 11:35am
Characterization and Dispersion of Human Expiratory Droplets – a Review
West Texas A&M University, United States of America
The paper reviews studies conducted on human expiratory droplets for the purpose of defining the characteristics of expiratory droplets, their maximum dispersion and the forces influencing that in an unventilated environment. The review shows coughing, sneezing and speaking droplets to have comparable size ranges, while breathing droplets have the narrowest size range. Sneezing droplets have the largest average size and highest velocity among expiratory droplets. Compiled data reveal droplet Froude number offers a plausible quantitative measure of the droplet maximum spread. The fate of the airborne droplets is seen to be dictated by an interplay between their inertial force and gravitational force. The higher the Froude number, the greater is the droplet spread. Small droplets with high flow inertia, such as dry sputum droplets, are capable of reaching longer horizontal distances in comparison to large droplets. The review shows the maximum horizontal distance coughing droplets can reach exceeds 2 m, while sneezing droplets can reach distances above 6 m, greater than the 2 m physical distancing currently adopted to avoid virus contamination.
11:35am - 11:40am
The potential of bio-based insulation products to support indoor air quality and reduce aerosol transmissions of contagious respiratory viruses such as SARS CoV-2 in the construction industry.
Avans University of Applied Science, The Netherlands
Almost half of absenteeism is caused by flu and catching colds. Previous studies have shown that aerosols can contain contagious respiratory viruses such as COVID-19. Theyhave a lighter weight than water vapor and that they can also be absorbed by it. When compared to insulation materials such as mineral wool, biobased materials can absorb and accumulate moisture. This property can help reduce the concentrations of vapor and aerosols in the building climate. With improved are quality and the reduction of aerosols containing respiratory viruses such as COVID-19 their spread can be limited and absenteeism due to flu and colds reduced.
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