Airborne spread of infectious agents in the indoor environment

Oral configuration-dependent variability of the metrics of exhaled respiratory droplets during a consecutive coughing event

BACKGROUND AND OBJECTIVE

Coughing events are eruptive sources of virus-laden droplets/droplet nuclei. These increase the risk of infection in susceptible individuals during airborne transmission. The oral cavity functions as an exit route for exhaled droplets. Thus, its configuration contributes significantly to the metrics of exhaled droplets.

METHODS

In this study, two realistic numerical models were developed: the respiratory system from the throat to the second bifurcation and the oral cavity with different anatomical structures. A coupling of Eulerian Wall Film (EWF) - Discrete Phase Model (DPM) was employed to numerically describe the generation, absorption and exhalation properties. In addition, two sequential coughing episodes were considered with variegated profiles in the second cough.

RESULTS

As a result, the enlargement of the oral cavity caused considerable alterations in the original spatial distribution and total number concentration of exhaled droplets: these were reduced by approximately 30 %. Considering the consecutive second cough, maintaining or decreasing the flow rates resulted in a decrease in the total quantity of exhalation droplets by 25-90 %. The variations in the oral structure or coughing flow profile also reallocated the local spatial and proportional distribution of exhaled droplet. The expelled droplets/droplet nuclei's size remained approximately 0.25-20 μm range with varied development trends even though the peak concentration reserved unchanged at approximately 5 μm.

CONCLUSIONS

This study is a substantial work emphasizing the dependent variability of oral geometry and coughing physiology related to the properties of exhaled droplets. It emphasizes the uncertainties in the input parameters required for indoor transmission risk studies related to intersubject variability.

Rapid virucidal activity of an air sanitizer against aerosolized MS2 and Phi6 phage surrogates for non-enveloped and enveloped vertebrate viruses, including SARS-CoV-2

An air sanitizer was evaluated using an aerobiology protocol, compliant with the U.S. Environmental Protection Agency's Air Sanitizer Guidelines, for virucidal activity against bacteriophages Phi6 and MS2 (used as surrogates for enveloped and non-enveloped human pathogenic viruses). The phages were suspended in a medium containing a tripartite soil load simulating body fluids and aerosolized using a six-jet Collison nebulizer in an enclosed 25 m3 aerobiology chamber at 22 ± 2°C and 50 ± 10% relative humidity. The air sanitizer was sprayed into the chamber for 30 s. Viable phages in the air were captured directly, in real time, on host bacterial lawns using a slit-to-agar sampler. Reductions in viable phage concentration ≥3.0 log10 (99.9%) were observed after a mean exposure of 3.6 min for Phi6, suggesting efficacy against enveloped viruses (e.g., SARS-CoV-2, influenza, and RSV), and ~10.6 min for MS2, suggesting virucidal efficacy for non-enveloped viruses (e.g., noroviruses and rhinoviruses). This targeted air sanitization approach represents an important non-pharmaceutical public health intervention with virucidal efficacy against airborne viral pathogens.IMPORTANCEAirborne viruses are implicated in the transmission indoors of respiratory and enteric viral infections. Air sanitizers represent a non-pharmaceutical intervention to mitigate the risk of such viral transmission. We have developed a method that is now an ASTM International standard (ASTM E3273-21) as well as a test protocol approved by the U.S. EPA to evaluate the efficacy of air sanitizing sprays for inactivating airborne MS2 and Phi6 bacteriophage (used as surrogates for non-enveloped and enveloped human pathogenic viruses, respectively). The test phages were individually suspended in a soil load and aerosolized into a room-sized aerobiology chamber maintained at ambient temperature and relative humidity. Reductions in viable phage concentration ≥3.0 log10 (99.9%) were observed after a mean exposure of 3.6 min for Phi6, suggesting efficacy against enveloped viruses (e.g., SARS-CoV-2; influenza; RSV), and ~10.6 min for MS2, suggesting virucidal efficacy for non-enveloped viruses (e.g., noroviruses and rhinoviruses). The data suggest the utility of the air sanitizer for mitigating the risk of indoor viral transmission during viral pandemics and outbreaks.

Open-set deep learning-enabled single-cell Raman spectroscopy for rapid identification of airborne pathogens in real-world environments

Pathogenic bioaerosols are critical for outbreaks of airborne disease; however, rapidly and accurately identifying pathogens directly from complex air environments remains highly challenging. We present an advanced method that combines open-set deep learning (OSDL) with single-cell Raman spectroscopy to identify pathogens in real-world air containing diverse unknown indigenous bacteria that cannot be fully included in training sets. To test and further enhance identification, we constructed the Raman datasets of aerosolized bacteria. Through optimizing OSDL algorithms and training strategies, Raman-OSDL achieves 93% accuracy for five target airborne pathogens, 84% accuracy for untrained air bacteria, and 36% reduction in false positive rates compared to conventional close-set algorithms. It offers a high detection sensitivity down to 1:1000. When applied to real air containing >4600 bacterial species, our method accurately identifies single or multiple pathogens simultaneously within an hour. This single-cell tool advances rapidly surveilling pathogens in complex environments to prevent infection transmission.

The role of human rhinovirus in COPD exacerbations in Abu Dhabi: molecular epidemiology and clinical significance

This study aimed to describe the molecular epidemiology and seasonality of human rhinovirus (HRV) in chronic obstructive pulmonary disease (COPD) and its association with COPD exacerbations in Abu Dhabi, the United Arab Emirates (UAE). Sputum specimens were collected for analysis from all COPD patients who visited a medical center from November 2021 to October 2022. The real-time quantitative polymerase chain reaction (qPCR) test was used to detect HRV. Of the 78 COPD patients included in the study, 58 (74%) patients presented with one or more exacerbation episodes. The incidence of COPD exacerbation peaked over the winter and substantially decreased during the summer. HRV positivity in patients during exacerbation (E1) was 11/58 (19%) and 15/58 (26%) two weeks after the exacerbation episode (E2). There was no significant difference in the HRV load in these patients. No statistically significant difference was observed in the detection of HRV during exacerbation compared to patients with stable COPD. This is the first study to assess the association between HRV detection by qPCR and COPD exacerbations in the UAE. The high sensitivity of the detection technology helped collect reliable epidemiologic data. Few studies have provided similar Middle East data. This study's pattern of COPD exacerbations and HRV detection parallels that of temperate countries. This information can help with future, more extensive surveillance of respiratory viruses in the UAE and the Middle East and their association with COPD exacerbations.

Resuspension and Dissemination of MS2 Virus from Flooring After Human Activities in Built Environment: Impact of Dust Particles

Resuspended particles from human activities can contribute to pathogen exposure via airborne fomite contamination in built environments. Studies investigating the dissemination of resuspended viruses are limited. The goal of this study was to explore viral dissemination after aerosolized resuspension via human activities on indoor flooring. Nylon carpet or wood flooring was seeded with virus (MS2) or virus laden dust then evaluated after activities, i.e., walking and vacuuming. Statistically significant differences were found in dispersal of virus laden dust after vacuuming carpet (p-value = 5.8 × 10-6) and wood (p-value = 0.003, distance > 12 in/30 cm). Significant differences were also found between floor materials and virus laden dust dispersal vacuuming (p = 2.09 × 10-5) and walking (p = 2.68 × 10-2). A quantitative microbial risk assessment (QMRA) scenario using Norovirus and a single fomite touch followed by a single hand-to-mouth touch indicated a statistically significant difference associated with virus laden dust particles and vacuuming carpet(p < 0.001). Infection risks were 1 to 5 log10 greater for dust exposure. The greatest risk reductions from fomites were seen across vacuuming carpet no-dust scenarios for surfaces <30 cm from flooring. More research is needed to determine the role resuspension plays in exposure and transmission of potentially infectious agents.

Recent Developments in Aptamer-Based Sensors for Diagnostics

Chronic and non-communicable diseases (NCDs) account for a large proportion of global disorders and mortality, posing significant burdens on healthcare systems. Early diagnosis and timely interference are critical for effective management and disease prevention. However, the traditional methods of diagnosis still suffer from high costs, time delays in processing, and infrastructure requirements that are usually unaffordable in resource-constrained settings. Aptamer-based biosensors have emerged as promising alternatives to offer enhanced specificity, stability, and cost-effectiveness for disease biomarker detection. The SELEX (Systematic Evolution of Ligands by Exponential Enrichment) methodology allows developing aptamers with high-affinity binding capabilities to a variety of targets, for instance proteins, cells, or even small molecules, hence rendering them suitable for NCD diagnosis. Aptasensors-recent developments in the electrochemical and optical dominion-offer much enhanced sensitivity, selectivity, and stability of detection across a diverse range of diseases from lung cancer and leukemia to diabetes and chronic respiratory disorders. This study provides a comprehensive review of progress in aptamer-based sensors, focusing on their role in point-of-care diagnostics and adaptability in a real-world environment with future directions in overcoming current limitations.

The Effect of Water Resistance Therapy on the Impulse Dispersion of Aerosols During Sustained Phonation

INTRODUCTION

Group singing has been associated with higher transmission risks via exhaled and spread aerosols in the CoVID19 pandemic. For this reason, many musical activities, such as rehearsals and lessons, but also voice therapy sessions, have been restricted in many countries. Consequently, transmission risks and pathways have been studied, such as aerosol amounts generated by exhalation tasks, convectional flows in rooms, or the impulse dispersion of different kinds of phonation. The use of water resistance exercises such as those utilizing LAX VOX®, are common in voice lessons and as vocal warm-ups. With this context, this study investigates the impulse dispersion characteristics of aerosols during a voiced water resistance exercise in comparison to normal singing.

METHODS

Twelve professional singers (six male, six female) were asked to phonate a stable pitch through a silicone tube into a bottle filled with water, holding the end of the tube 5 cm below the surface. Before performing the tasks, the singers inhaled the vapor consisting of 0.5 L base liquid from an e-cigarette. The exhaled gas cloud coming out of the bottle was recorded in all three spatial directions and the dispersion was measured as a function of time.

RESULTS

At the end of the phonation task, the median distance to the front was 0.55 m and the median of the lateral expansion of the cloud was 0.89 m, the maximum to the front reached 0.88 m, and the maximum of lateral expansion 1.05 m. For the upwards direction of the clouds a median of 1.00 m and a maximum of 1.34 m from the mouth were measured. Three seconds after the end of the task, the medians were declining.

CONCLUSION

The exhaled aerosol cloud can expand despite the obstacle of the water when using LAX VOX® during phonation.

What influences the close contact between health care workers and patients? An observational study in a hospital dental outpatient department

BACKGROUND

Dental outpatient departments, characterized by close proximity and unmasked patients, present a considerable risk of respiratory infections for health care workers (HCWs). However, the lack of comprehensive data on close contact (<1.5m) between HCWs and patients poses a significant obstacle to the development of targeted control strategies.

METHODS

An observation study was conducted at a hospital in Shenzhen, China, utilizing depth cameras with machine learning to capture close-contact behaviors of patients with HCWs. Additionally, questionnaires were administered to collect patient demographics.

RESULTS

The study included 200 patients, 10 dental practitioners, and 10 nurses. Patients had significantly higher close-contact rates with dental practitioners (97.5%) compared with nurses (72.8%, P < .001). The reason for the visit significantly influenced patient-practitioner (P = .018) and patient-nurse (P = .007) close-contact time, with the highest values observed in prosthodontics and orthodontics patients. Furthermore, patient age also significantly impacted the close-contact rate with nurses (P = .024), with the highest rate observed in patients below 14 years old at 85% [interquartile range: 70-93].

CONCLUSIONS

Dental outpatient departments exhibit high HCW-patient close-contact rates, influenced by visit purpose and patient age. Enhanced infection control measures are warranted, particularly for prosthodontics and orthodontics patients or those below 14 years old.

The Determination of the Rapid and Effective Activity of an Air Sanitizer against Aerosolized Bacteria Using a Room-Sized Aerobiology Chamber

Air sanitization is an important non-pharmaceutical intervention for mitigating the risk of indoor pathogen spreading. A dipropylene glycol-containing air sanitizer was tested against aerosolized Staphylococcus aureus and Klebsiella pneumoniae. The bacteria, suspended in a soil load, were aerosolized using a six-jet Collison nebulizer with pressurized air. The 25-m3 (~900 ft3) aerobiology chamber was maintained at 22 ± 2 °C and 50 ± 5% relative humidity per the U.S. Environmental Protection Agency's 2012 Guidelines on air sanitizers. An initial 2-min air sample was collected from the chamber using a slit-to-agar sampler containing 150-mm Petri plates, with Trypticase soy agar (TSA) containing neutralizers to quench the microbicidal activity of the air sanitizer, to determine the initial bacterial challenge in the air. The air sanitizer was sprayed into the chamber from pressurized cans. Additional air samples were collected from the chamber over 10 min to detect surviving bacteria. The TSA plates were then incubated aerobically at 36 ± 1 °C for 90 ± 4 h and scored for bacterial colony-forming units. A 30-s spray of the air sanitizer reduced infectious S. aureus and K. pneumoniae titers by 3.0 log10 (99.9%) in 3.2 ± 0.3 min and 1.2 ± 0.0 min, respectively. Based on these findings, the EPA granted registration of the air sanitizer as the first product of its kind for indoor air sanitization.

Natural and socio-environmental factors in the transmission of COVID-19: a comprehensive analysis of epidemiology and mechanisms

PURPOSE OF REVIEW

There are significant differences in the transmission rate and mortality rate of COVID-19 under environmental conditions such as seasons and climates. However, the impact of environmental factors on the role of the COVID-19 pandemic and the transmission mechanism of the SARS-CoV-2 is unclear. Therefore, a comprehensive understanding of the impact of environmental factors on COVID-19 can provide innovative insights for global epidemic prevention and control policies and COVID-19 related research. This review summarizes the evidence of the impact of different natural and social environmental factors on the transmission of COVID-19 through a comprehensive analysis of epidemiology and mechanism research. This will provide innovative inspiration for global epidemic prevention and control policies and provide reference for similar infectious diseases that may emerge in the future.

RECENT FINDINGS

Evidence reveals mechanisms by which natural environmental factors influence the transmission of COVID-19, including (i) virus survival and transport, (ii) immune system damage, (iii) inflammation, oxidative stress, and cell death, and (iiii) increasing risk of complications. All of these measures appear to be effective in controlling the spread or mortality of COVID-19: (1) reducing air pollution levels, (2) rational use of ozone disinfection and medical ozone therapy, (3) rational exposure to sunlight, (4) scientific ventilation and maintenance of indoor temperature and humidity, (5) control of population density, and (6) control of population movement. Our review indicates that with the continuous mutation of SARS-CoV-2, high temperature, high humidity, low air pollution levels, and low population density more likely to slow down the spread of the virus.

Impact of artificial accelerated ageing of PVC surfaces and surface degradation on disinfectant efficacy

BACKGROUND

Standardized efficacy surface tests for disinfectants are performed on pristine surfaces. There is a growing interest in understanding the impact of surface ageing on disinfectant activity, owing for example to the increased usage of ultraviolet (UV) radiation and oxidative chemistries for surface decontamination. This acknowledges that general surface 'wear and tear' following UV radiation and oxidative biocide exposure may impact biocidal product efficacy.

METHODS

PVC surfaces were aged through thermal and UV-A radiation (340 nm wavelength) following the use of standard ageing surface protocols to simulate natural surface degradation. Surface roughness, contact angle and scanning electron microscopy were performed to evaluate physical changes in PVC surfaces before and after artificial ageing. The efficacy of five pre-impregnated disinfectant wipes were evaluated using the ASTM E2967-15 on stainless-steel (control) and PVC surfaces (aged and non-aged).

RESULTS

The type of formulation and the organism tested remained the most significant factors impacting disinfectant efficacy, compared with surface type. Both thermal ageing and UV-A exposure of PVC surfaces clearly showed signs of surface degradation, notably an increase in surface roughness. Physical changes were observed in the roughness of PVC after artificial ageing. A difference in disinfectant efficacy dependent on aged PVC surfaces was observed for some, but not all formulations.

CONCLUSION

We showed that surface type and surface ageing can affect biocidal product efficacy, although in a non-predictable manner. More research is needed in this field to ascertain whether surface types and aged surfaces should be used in standardized efficacy testing.

Expanding the focus of the One Health concept: links between the Earth-system processes of the planetary boundaries framework and antibiotic resistance

The scientific community warns that our impact on planet Earth is so acute that we are crossing several of the planetary boundaries that demarcate the safe operating space for humankind. Besides, there is mounting evidence of serious effects on people's health derived from the ongoing environmental degradation. Regarding human health, the spread of antibiotic resistant bacteria is one of the most critical public health issues worldwide. Relevantly, antibiotic resistance has been claimed to be the quintessential One Health issue. The One Health concept links human, animal, and environmental health, but it is frequently only focused on the risk of zoonotic pathogens to public health or, to a lesser extent, the impact of contaminants on human health, i.e., adverse effects on human health coming from the other two One Health "compartments". It is recurrently claimed that antibiotic resistance must be approached from a One Health perspective, but such statement often only refers to the connection between the use of antibiotics in veterinary practice and the antibiotic resistance crisis, or the impact of contaminants (antibiotics, heavy metals, disinfectants, etc.) on antibiotic resistance. Nonetheless, the nine Earth-system processes considered in the planetary boundaries framework can be directly or indirectly linked to antibiotic resistance. Here, some of the main links between those processes and the dissemination of antibiotic resistance are described. The ultimate goal is to expand the focus of the One Health concept by pointing out the links between critical Earth-system processes and the One Health quintessential issue, i.e., antibiotic resistance.

The airborne transmission of viruses causes tight transmission bottlenecks

The transmission bottleneck describes the number of viral particles that initiate an infection in a new host. Previous studies have used genome sequence data to suggest that transmission bottlenecks for influenza and SARS-CoV-2 involve few viral particles, but the general principles of virus transmission are not fully understood. Here we show that, across a broad range of circumstances, tight transmission bottlenecks are a simple consequence of the physical process of airborne viral transmission. We use mathematical modelling to describe the physical process of the emission and inhalation of infectious particles, deriving the result that that the great majority of transmission bottlenecks involve few viral particles. While exceptions to this rule exist, the circumstances needed to create these exceptions are likely very rare. We thus provide a physical explanation for previous inferences of bottleneck size, while predicting that tight transmission bottlenecks prevail more generally in respiratory virus transmission.

In silico identification of viral loads in cough-generated droplets - Seamless integrated analysis of CFPD-HCD-EWF

BACKGROUND AND OBJECTIVE

Respiratory diseases caused by respiratory viruses have significantly threatened public health worldwide. This study presents a comprehensive approach to predict viral dynamics and the generation of stripped droplets within the mucus layer of the respiratory tract during coughing using a larynx-trachea-bifurcation (LTB) model.

METHODS

This study integrates computational fluid-particle dynamics (CFPD), host-cell dynamics (HCD), and the Eulerian wall film (EWF) model to propose a potential means for seamless integrated analysis. The verified CFPD-HCD coupling model based on a 3D-shell model was used to characterize the severe acute respiratory syndrome, coronavirus 2 (SARS-CoV-2) dynamics in the LTB mucus layer, whereas the EWF model was employed to account for the interfacial fluid to explore the generation mechanism and trace the origin site of droplets exhaled during a coughing event of an infected host.

RESULTS

The results obtained using CFPD delineated the preferential deposition sites for droplets in the laryngeal and tracheal regions. Thus, the analysis of the HCD model showed that the viral load increased rapidly in the laryngeal region during the peak of infection, whereas there was a growth delay in the tracheal region (up to day 8 after infection). After two weeks of infection, the high viral load gradually migrated towards the glottic region. Interestingly, the EWF model demonstrated a high concentration of exhaled droplets originating from the larynx. The coupling technique indicated a concurrent high viral load in the mucus layer and site of origin of the exhaled droplets.

CONCLUSIONS

This interdisciplinary research underscores the seamless analysis from initial exposure to virus-laden droplets, the dynamics of viral infection in the LTB mucus layer, and the re-emission from the coughing activities of an infected host. Our efforts aimed to address the complex challenges at the intersection of viral dynamics and respiratory health, which can contribute to a more detailed understanding and targeted prevention of respiratory diseases.

Development of a standard evaluation method for microbial UV sensitivity using light-emitting diodes

Ultraviolet (UV) light is an effective disinfection method. In particular, UV light-emitting diodes (UV-LEDs) are expected to have many applications as light sources owing to their compact form factor and wide range of choices of wavelengths. However, the UV sensitivity of microorganisms for each UV wavelength has not been evaluated comprehensively because standard experimental conditions based on LED characteristics have not been established. Therefore, it is necessary to establish a standard evaluation method based on LED characteristics. Here, we developed a new UV-LED device based on strictly controlled irradiation conditions using LEDs for each wavelength (250-365 nm), checked the validity of the device characteristics and evaluated the UV sensitivity of Escherichia coli using this new evaluation method. For this new device, we considered accurate irradiance, accurate spectra, irradiance uniformity, accurate dose, beam angle, surrounding material reflections, and sample condition. From our results, the following UV irradiation conditions were established as standard: 1 mW/cm2 irradiance, bacterial solution with absorbance value of A600 = 0.5 diluted 10 times solution, solution volume of 1 mL, working distance (WD) of 100 mm. In order to compare the effects of irradiation under uniform conditions on inactivation of microorganisms, we assessed inactivation effect of E. coli by LED irradiation at each wavelength using the U280 LED as a standard wavelength. The inactivation effect for U280 LED irradiation was -0.95 ± 0.21 log at a dose of 4 mJ/cm2. Under this condition of dose, our results showed a high wavelength dependence of the inactivation effect at each UV wavelength peaking at 267 nm. Our study showed that this irradiation system was validated for the standard UV irradiation system and could be contributed to the establishment of food and water hygiene control methods and the development of equipment for the prevention of infectious diseases.

Indoor air humidity revisited: Impact on acute symptoms, work productivity, and risk of influenza and COVID-19 infection

Recent epidemiological and experimental findings reconfirm that low indoor air humidity (dry air) increases the prevalence of acute eye and airway symptoms in offices, result in lower mucociliary clearance in the airways, less efficient immune defense, and deteriorate the work productivity. New epidemiological and experimental research also support that the environmental conditions for the risk of infection of influenza and COVID-19 virus is lowest in the Goldilocks zone of 40-60% relative humidity (RH) by decrease of the airways' susceptibility, which can be elevated by particle exposure. Furthermore, low RH increases the generation of infectious virus laden aerosols exhaled from infected people. In general, elevation of the indoor air humidity from dry air increases the health of the airways concomitantly with lower viability of infectious virus. Thus, the negative effects of ventilation with dry outdoor air (low absolute air humidity) should be assessed according to 1) weakened health and functionality of the airways, 2) increased viability and possible increased transmissibility of infectious virus, and 3) evaporation of virus containing droplets to dry out to droplet nuclei (also possible at high room temperature), which increases their floating time in the indoor air. The removal of acid-containing ambient aerosols from the indoor air by filtration increases pH, viability of infectious viruses, and the risk of infection, which synergistically may further increase by particle exposure. Thus, the dilution of indoor air pollutants and virus aerosols by dry outdoor air ventilation should be assessed and compared with the beneficial health effects by control of the center zone of 40-60% RH, an essential factor for optimal functionality of the airways, and with the additional positive impact on acute symptoms, work productivity, and reduced risk of infection.

Airborne respiratory aerosol transport and deposition in a two-person office using a novel diffusion-based numerical model

BACKGROUND

The COVID-19 pandemic was caused by the SARS-CoV-2 coronaviruses transmitted mainly through exposure to airborne respiratory droplets and aerosols carrying the virus.

OBJECTIVE

To assess the transport and dispersion of respiratory aerosols containing the SARS-CoV-2 virus and other viruses in a small office space using a diffusion-based computational modeling approach.

METHODS

A 3-D computational model was used to simulate the airflow inside the 70.2 m3 ventilated office. A novel diffusion model accounting for turbulence dispersion and gravitational sedimentation was utilized to predict droplet concentration transport and deposition. The numerical model was validated and used to investigate the influences of partition height and different ventilation rates on the concentration of respiratory aerosols of various sizes (1, 10, 20, and 50 µm) emitted by continuous speaking.

RESULTS

An increase in the hourly air change rate (ACH) from 2.0 to 5.6 decreased the 1 μm droplet concentration inside the office by a factor of 2.8 and in the breathing zone of the receptor occupant by a factor of 3.2. The concentration at the receptor breathing zone is estimated by the area-weighted average of a 1 m diameter circular disk, with its centroid at the center of the receptor mannequin mouth. While all aerosols were dispersed by airflow turbulence, the gravitational sedimentation significantly influenced the transport of larger aerosols in the room. The 1 and 10 μm aerosols remained suspended in the air and dispersed throughout the room. In contrast, the larger 20 and 50 μm aerosols deposited on the floor quickly due to the gravitational sedimentation. Increasing the partition between cubicles by 0.254 m (10") has little effect on the smaller aerosols and overall exposure.

IMPACT

This paper provides an efficient computational model for analyzing the concentration of different respiratory droplets and aerosols in an indoor environment. Thus, the approach could be used for assessing the influence of the spatial concentration variations on exposure for which the fully mixed model cannot be used.

Risk factors for SARS-CoV-2 transmission during a movie theater outbreak in Incheon in the Republic of Korea, November 2021: a retrospective study

BACKGROUND

We examined factors contributing to the transmission of an acute respiratory virus within multi-use facilities, focusing on an outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a movie theater in the Republic of Korea.

METHODS

This retrospective cohort study involved a descriptive analysis of 48 confirmed cases. Logistic regression was applied to a cohort of 80 theater attendees to identify risk factors for infection. The infection source and transmission route were determined through gene sequencing data analysis.

RESULTS

Of the 48 confirmed cases, 35 were theater attendees (72.9%), 10 were family members of attendees (20.8%), 2 were friends (4.2%), and 1 was an employee (2.1%). Among the 80 individuals who attended the 3rd to 5th screenings of the day, 35 became infected, representing a 43.8% attack rate. Specifically, 28 of the 33 third-screening attendees developed confirmed SARSCoV-2, constituting an 84.8% attack rate. Furthermore, 11 of the 12 cases epidemiologically linked to the theater outbreak were clustered monophyletically within the AY.69 lineage. At the time of the screening, 35 individuals (72.9%) had received 2 vaccine doses. However, vaccination status did not significantly influence infection risk. Multivariate analysis revealed that close contacts had a 15.9-fold higher risk of infection (95% confidence interval, 4.37-78.39) than casual contacts.

CONCLUSION

SARS-CoV-2 transmission occurred within the theater, and extended into the community, via a moviegoer who attended the 3rd screening during the viral incubation period after contracting the virus from a family member. This study emphasizes the importance of adequate ventilation in theaters.

A Review of the Evidence on the Role of Floors and Shoes in the Dissemination of Pathogens in a Healthcare Setting

Background: It is generally accepted that shoes and floors are contaminated with pathogens including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Clostridium difficile, yet correlation to clinical infection is not well established. Because floors and shoes are low-touch surfaces, these are considered non-critical surfaces for cleaning and disinfection. The purpose of this review is to assess peer-reviewed literature inclusive of floors and shoe soles as contributors to the dissemination of infectious pathogens within healthcare settings. Methods: Using the Preferred Reporting Items for Systematic Reviews (PRISMA) methodology, PubMed and Medline were searched for articles assessing the presence of pathogens on or the transmission of pathogens between or from floors or shoe soles/shoe covers. Inclusion criteria are the human population within healthcare or controlled experimental settings after 1999 and available in English. Results: Four hundred eighteen articles were screened, and 18 articles documented recovery of bacterial and viral pathogens from both floors and shoes. Seventy-two percent (13/18) of these were published after 2015, showing increased consideration of the transfer of pathogens to high-touch surfaces from shoe soles or floors during patient care. Conclusions: There is evidence that floors and shoes in healthcare settings are contaminated with several different species of health-care-associated pathogens including MRSA, VRE, and Clostridium difficile.

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

BACKGROUND

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.

MATERIAL AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

The Presence of Legionella in Water Used for Car Washing: Implications for Public Health

Although today all of the aspects of Legionella are better understood than in the past, in many countries the interest is still mainly focused on healthcare and tourism facilities. Other at-risk areas are less explored, such as those where workers are often in contact with water during their activities. In reality, any water system capable of producing aerosols can be considered a potential source of Legionella transmission, including car washes, where a large number of users work and flow through annually. From January to May 2022, 120 samples were carried out in 30 car washes located in Messina (Italy): 60 samples of water and 60 of aerosols. The aim of this investigation was to evaluate the risk of legionellosis in car washing workers exposed to potentially contaminated aerosols. To increase the probability of finding Legionella, the sample collections were organized on different days of the week. Of the total samples taken, 10 (8.3%) were positive for Legionella: seven (11.7%) water (range 100-1000 CFU) and three (5%) aerosol (range 10-150 CFU) samples. Detected serogroups were L. pneumophila sgr 1, 7, 10 and Legionella gormanii. Given the results obtained, preventative measures should be implemented in such facilities in order to protect the health of users and car wash operators.

Assessing airborne transmission risks in COVID-19 hospitals by systematically monitoring SARS-CoV-2 in the air

IMPORTANCE

Risk management and control of airborne transmission in hospitals is crucial in response to a respiratory virus pandemic. However, the formulation of these infection control measures is often based on epidemiological investigations, which are an indirect way of analyzing the transmission route of viruses. This can lead to careless omissions in infection prevention and control or excessively restrictive measures that increase the burden on healthcare workers. The study provides a starting point for standardizing transmission risk management in designated hospitals by systemically monitoring viruses in the air of typical spaces in COVID-19 hospitals. The negative results of 359 air samples in the clean and emergency zones demonstrated the existing measures to interrupt airborne transmission in a designated COVID-19 hospital. Some positive cases in the corridor of the contaminant zone during rounds and meal delivery highlighted the importance of monitoring airborne viruses for interrupting nosocomial infection.

Perspectives on human movement considerations in indoor airflow assessment: a comprehensive data-driven systematic review

Understanding particle dispersion characteristics in indoor environments is crucial for revising infection prevention guidelines through optimized engineering control. The secondary wake flow induced by human movements can disrupt the local airflow field, which enhances particle dispersion within indoor spaces. Over the years, researchers have explored the impact of human movement on indoor air quality (IAQ) and identified noteworthy findings. However, there is a lack of a comprehensive review that systematically synthesizes and summarizes the research in this field. This paper aims to fill that gap by providing an overview of the topic and shedding light on emerging areas. Through a systematic review of relevant articles from the Web of Science database, the study findings reveal an emerging trend and current research gaps on the topic titled Impact of Human Movement in Indoor Airflow (HMIA). As an overview, this paper explores the effect of human movement on human microenvironments and particle resuspension in indoor environments. It delves into the currently available methods for assessing the HMIA and proposes the integration of IoT sensors for potential indoor airflow monitoring. The present study also emphasizes incorporating human movement into ventilation studies to achieve more realistic predictions and yield more practical measures. This review advances knowledge and holds significant implications for scientific and public communities. It identifies future research directions and facilitates the development of effective ventilation strategies to enhance indoor environments and safeguard public health.

Addressing the challenges in implementing airborne infection control guidelines and embracing the policies

Airborne pathogens not only lead to epidemics and pandemics, but are associated with morbidity and mortality. Administrative or managerial control, environmental control and use of personal protective equipments are the three components in airborne infection control. National and international guidelines for ideal airborne infection control (AIC) practices are available for more than a decade; however the implementation of these need to be looked into, challenges identified and addressed for effective prevention of airborne disease transmission. Commitment of multiple stakeholders from policy makers to patients, budget allocation and adequate fund flow, functioning AIC committees at multiple levels with an inbuilt reporting and monitoring mechanism, adaptation of the AIC practices at various health care levels, supportive supervision, training and ongoing education for health care providers, behaviour change communication to patients to adapt the practices at health care facility level, by health care personnel and patients will facilitate health system preparedness for handling any emergencies, but will also help in reducing the burden of persisting airborne diseases such as tuberculosis. Operational research in this least focused area will also help to identify and address the challenges.

Consideration on size, velocity and path of droplets emitted during running

BACKGROUND

People began to wear face masks during physical activities due to spread of COVID-19. There are no previous studies about the need for wearing masks while running.

METHODS

Assuming a citizen runner who runs full marathon in 4 hours, we verified the path and the amount of droplet dispersal, setting a humanoid mannequin with a mask in simulated running environment (Experiment 1). We also had six adults exercise in the same environment to examine droplet behaviors when not wearing a face mask (Experiment 2). Average droplet size was determined, and repeated measures ANOVA was carried out to examine statistical significance. To evaluate observed droplet behaviors, theoretical solutions of the downfall motion of large droplets were then derived, taking air resistance into consideration.

RESULTS

Experiment 1: wearing a face mask caused more droplets to adhere to the face; Experiment 2: droplets were emitted in conversation, coughing or sneezing, and they fell within social distancing. Average droplet size was not sensitive to the wind velocity. It could vary with a significant difference for time and wind velocity. Observed velocity and path of droplet can be expressed by the theoretical solutions.

CONCLUSIONS

Velocity and path of large droplets can be expressed by the theoretical solution of particles in downfall motion under air resistance. We therefore conclude that wearing a mask while running gives adverse effects in preventing infection. Possibility of droplet transmission while running is considered low even when not wearing a face mask, as long as social distancing is ensured.

Characterizing infection risk in a restaurant environment due to airborne diseases using discrete droplet dispersion simulations

The use of masks as a measure to control the spread of respiratory viruses has been widely acknowledged. However, there are instances where wearing a mask is not possible, making these environments potential vectors for virus transmission. Such environments can contain multiple sources of infection and are challenging to characterize in terms of infection risk. To address this issue, we have developed a methodology to investigate the role of ventilation in reducing the infection risk in such environments. We use a restaurant setting as a representative scenario to demonstrate the methodology. Using implicit large eddy simulations along with discrete droplet dispersion modeling we investigate the impact of ventilation and physical distance on the spread of respiratory viruses and the risk of infection. Our findings show that operating ventilation systems, such as mechanical mixing and increasing physical distance between subjects, can significantly reduce the average room infection risk and number of newly infected subjects. However, this observation is subject to the transmissibility of the airborne viruses. In the case of a highly transmissible virus, the use of mechanical mixing may be inconsequential when compared to only fresh air ventilation. These findings provide valuable insights into the mitigation of infection risk in situations where the use of masks is not possible.

[Respiratory infections: Additional transmission-based precautions in healthcare facilities]

INTRODUCTION

In health care, measures against cross-transmission of microorganisms are codified by standard precautions, and if necessary, they are supplemented by additional precautions.

STATE OF THE ART

Several factors impact transmission of microorganisms via the respiratory route: size and quantity of the emitted particles, environmental conditions, nature and pathogenicity of the microorganisms, and degree of host receptivity. While some microorganisms necessitate additional airborne or droplet precautions, others do not.

PROSPECTS

For most microorganisms, transmission patterns are well-understood and transmission-based precautions are well-established. For others, measures to prevent cross-transmission in healthcare facilities remain under discussion.

CONCLUSIONS

Standard precautions are essential to the prevention of microorganism transmission. Understanding of the modalities of microorganism transmission is essential to implementation of additional transmission-based precautions, particularly in view of opting for appropriate respiratory protection.

Does attendance in outdoor kindergartens reduce the use of antibiotics in children?

AIM

The aim of this study was to determine whether children enrolled in rural outdoor kindergartens had a lower risk of redeeming at least one prescription for antibiotics compared with children enrolled in urban conventional kindergartens, and if type of antibiotics prescribed differed according to kindergarten type.

METHODS

Two Danish municipalities provided data including civil registration numbers from children enrolled in a rural outdoor kindergarten in 2011-2019, and a subsample of all children enrolled in urban conventional kindergartens in the same period. Civil registration numbers were linked to individual-level information on redeemed prescriptions for antibiotics from the Danish National Prescription Registry. Regression models were performed on 2132 children enrolled in outdoor kindergartens, and 2208 children enrolled in conventional kindergartens.

RESULTS

There was no difference between groups in risk of redeeming at least one prescription for all types of antibiotics (adjusted risk ratio: 0.97 [95% confidence intervals 0.93, 1.02, p = 0.26]). Similarly, there were no differences between kindergarten type and risk of redeeming at least one prescription for systemic, narrow-spectrum systemic antibacterial, broad-spectrum systemic antibacterial or topical antibiotics.

CONCLUSION

Compared with children who were enrolled in conventional kindergartens, children who were enrolled in outdoor kindergartens did not have a lower risk of redeeming prescriptions for any type of antibiotics.

Comparison of Zinc Oxide Nanoparticle Integration into Non-Woven Fabrics Using Different Functionalisation Methods for Prospective Application as Active Facemasks

The development of advanced facemasks stands out as a paramount priority in enhancing healthcare preparedness. In this work, different polypropylene non-woven fabrics (NWF) were characterised regarding their structural, physicochemical and comfort-related properties. The selected NWF for the intermediate layer was functionalised with zinc oxide nanoparticles (ZnO NPs) 0.3 and 1.2wt% using three different methods: electrospinning, dip-pad-dry and exhaustion. After the confirmation of ZnO NP content and distribution within the textile fibres by morphological and chemical analysis, the samples were evaluated regarding their antimicrobial properties. The functionalised fabrics obtained via dip-pad-dry unveiled the most promising data, with 0.017 ± 0.013wt% ZnO NPs being mostly located at the fibre's surface and capable of total eradication of Staphylococcus aureus and Escherichia coli colonies within the tested 24 h (ISO 22196 standard), as well as significantly contributing (**** p < 0.0001) to the growth inhibition of the bacteriophage MS2, a surrogate of the SARS-CoV-2 virus (ISO 18184 standard). A three-layered structure was assembled and thermoformed to obtain facemasks combining the previously chosen NWF, and its resulting antimicrobial capacity, filtration efficiency and breathability (NP EN ISO 149) were assessed. The developed three-layered and multiscaled fibrous structures with antimicrobial capacities hold immense potential as active individual protection facemasks.

Electrochemical aptasensors for pathogenic detection toward point-of-care diagnostics

A biosensor system refers to a biomedical device, which detects biological, chemical, or biochemical components by converting those signals to an electrical signal by utilizing and uniting physical or chemical transducer with biorecognition elements. An electrochemical biosensor is generally based on the reaction of either production or consumption of electrons under a three-electrode system. Biosensor systems are exploited in a wide range of areas, such as medicine, agriculture, husbandry, food, industry, environment protection, quality control, waste disposal, and the military. Pathogenic infections are the third leading cause of death worldwide after cardiovascular diseases and cancer. Therefore, there is an urgent need for effective diagnostic tools to control food, water, and soil contamination result in protecting human life and health. Aptamers are peptide or oligonucleotide-based molecules that show very high affinity to their targets that are produced from large pools of random amino acid or oligonucleotide sequences. Generally, aptamers have been utilized for fundamental sciences and clinical implementations for their target-specific affinity and have been intensely exploited for different kinds of biosensor applications for approximately 30 years. The convergence of aptamers with biosensor systems enabled the construction of voltammetric, amperometric, and impedimetric biosensors for the detection of specific pathogens. In this review, electrochemical aptamer biosensors were evaluated by discussing the definition, types, and production techniques of aptamers, the advantages of aptamers as a biological recognition element against their alternatives, and a wide range of aptasensor examples from literature in the detection of specific pathogens.

Investigation of bimodal characteristics of the droplet size distribution in condensation spray

To understand the generation process of airborne droplets during exhalation, this study investigates the mechanism of bimodal characteristics of the size distribution of droplets generated in a condensed spray flow. The phase change process in the condensed spray flow was estimated based on the droplet size distribution measured by a phase Doppler particle analyzer and the temperature distribution measured by a thermistor. On the central axis, the size distribution was unimodal in the spray interior. In contrast, bimodality of the size distribution at the outer edge of the spray flow was observed. At the edge of the spray flow, a large temperature gradient was formed. This indicates that condensation actively occurred at the outer edge. For the same reason as outlined above, condensation did not progress at the spray center because of the consumption of water vapor at the outer edge by the condensation, and the droplet diameter did not change significantly. Hence, owing to the difference in the local phase change process between the center and outer edge of the spray, large and small droplets can exist simultaneously in the middle region. As a result, the size distribution of the condensation spray is bimodal.

Dental professionals' use of personal protective equipment during COVID-19: a cross-sectional study in China

Background

Appropriate use of personal protective equipment (PPE) could significantly reduce the risk of viral transmission and infection. This study aimed to assess the use of PPE among dentists during the COVID-19 pandemic in China, explore its influencing factors, and provide some practical recommendations.

Methods

An online cross-sectional survey was conducted among 384 Chinese dentists in September 2022. The questionnaire comprised a series of questions about demographic characteristics, compliance with proper PPE use, personal barriers to use, and exposure risk estimation.

Results

Of the 384 respondents, 57.3% had unacceptable compliance with the proper use of PPE during COVID-19. Medical surgical mask is the most common for dental professionals to wear (93.8%), followed by goggles or face shield (63.8%), and isolation gown (53.1%). Unexpectedly, only 63.3% of respondents always change masks with guidelines. The condition for changing goggles/face shields and isolation gowns is even worse (45.6 and 37.0%, respectively). Visual barriers, physical discomfort, complex procedures, and heavy workload were the most common personal barriers to use. According to the results of Chi-square test and correlation analysis, PPE use compliance was associated with age, years of practice, medical institution type, and exposure risk estimation.

Conclusion

Chinese dental professionals need to improve their compliance with the proper use of PPE, especially those in the 31-40 age group, with 11-15 experience years and working in private dental clinics. Increasing compliance with PPE may be achieved by addressing personal barriers to use, human resource shortages, and perceptions of exposure risk.

Transmission of droplet aerosols in an elevator cabin: Effect of the ventilation mode

The recent outbreak of COVID-19 has threatened public health. Owing to the relatively sealed environment and poor ventilation in elevator cabins, passengers are at risk of respiratory tract infection. However, the distribution and dispersion of droplet aerosols in elevator cabins remain unclear. This study investigated the transmission of droplet aerosols exhaled by a source patient under three ventilation modes. Droplet aerosols produced by nose breathing and mouth coughing were resolved using computational fluid dynamics (CFD) simulations. We adopted the verified renormalization group (RNG) k-ε turbulence model to simulate the flow field and the Lagrangian method to track the droplet aerosols. In addition, the influence of the ventilation mode on droplet transmission was evaluated. The results showed that droplet aerosols gathered in the elevator cabin and were difficult to discharge under the mixed and displacement ventilation modes with specific initial conditions. The inhalation proportion of droplet aerosols for air curtain was 0.016%, which was significantly lower than that for mixed ventilation (0.049%) and displacement ventilation (0.071%). The air curtain confined the transmission of droplet aerosols with the minimum ratios of inhalation, deposition, and suspension and is thus recommended to reduce the exposure risk.

Safe CO2 threshold limits for indoor long-range airborne transmission control of COVID-19

CO2-based infection risk monitoring is highly recommended during the current COVID-19 pandemic. However, the CO2 monitoring thresholds proposed in the literature are mainly for spaces with fixed occupants. Determining CO2 threshold is challenging in spaces with changing occupancy due to the co-existence of quanta and CO2 remaining from previous occupants. Here, we propose a new calculation framework for deriving safe excess CO2 thresholds (above outdoor level), C t, for various spaces with fixed/changing occupancy and analyze the uncertainty involved. We categorized common indoor spaces into three scenarios based on their occupancy conditions, e.g., fixed or varying infection ratios (infectors/occupants). We proved that the rebreathed fraction-based model can be applied directly for deriving C t in the case of a fixed infection ratio (Scenario 1 and Scenario 2). In the case of varying infection ratios (Scenario 3), C t derivation must follow the general calculation framework due to the existence of initial quanta/excess CO2. Otherwise, C t can be significantly biased (e.g., 260 ppm) when the infection ratio varies greatly. C t can vary significantly based on specific space factors such as occupant number, physical activity, and community prevalence, e.g., 7 ppm for gym and 890 ppm for lecture hall, indicating C t must be determined on a case-by-case basis. An uncertainty of up to 6 orders of magnitude for C t was found for all cases due to uncertainty in emissions of quanta and CO2, thus emphasizing the role of accurate emissions data in determining C t.

A review on indoor airborne transmission of COVID-19– modelling and mitigation approaches

In the past few years, significant efforts have been made to investigate the transmission of COVID-19. This paper provides a review of the COVID-19 airborne transmission modeling and mitigation strategies. The simulation models here are classified into airborne transmission infectious risk models and numerical approaches for spatiotemporal airborne transmissions. Mathematical descriptions and assumptions on which these models have been based are discussed. Input data used in previous simulation studies to assess the dispersion of COVID-19 are extracted and reported. Moreover, measurements performed to study the COVID-19 airborne transmission within indoor environments are introduced to support validations for anticipated future modeling studies. Transmission mitigation strategies recommended in recent studies have been classified to include modifying occupancy and ventilation operations, using filters and air purifiers, installing ultraviolet (UV) air disinfection systems, and personal protection compliance, such as wearing masks and social distancing. The application of mitigation strategies to various building types, such as educational, office, public, residential, and hospital, is reviewed. Recommendations for future works are also discussed based on the current apparent knowledge gaps covering both modeling and mitigation approaches. Our findings show that different transmission mitigation measures were recommended for various indoor environments; however, there is no conclusive work reporting their combined effects on the level of mitigation that may be achieved. Moreover, further studies should be conducted to understand better the balance between approaches to mitigating the viral transmissions in buildings and building energy consumption.

Tracing the origin of large respiratory droplets by their deposition characteristics inside the respiratory tract during speech

Origin of differently sized respiratory droplets is fundamental for clarifying their viral loads and the sequential transmission mechanism of SARS-CoV-2 in indoor environments. Transient talking activities characterized by low (0.2 L/s), medium (0.9 L/s), and high (1.6 L/s) airflow rates of monosyllabic and successive syllabic vocalizations were investigated by computational fluid dynamics (CFD) simulations based on a real human airway model. SST k-ω model was chosen to predict the airflow field, and the discrete phase model (DPM) was used to calculate the trajectories of droplets within the respiratory tract. The results showed that flow field in the respiratory tract during speech is characterized by a significant laryngeal jet, and bronchi, larynx, and pharynx-larynx junction were main deposition sites for droplets released from the lower respiratory tract or around the vocal cords, and among which, over 90% of droplets over 5 µm released from vocal cords deposited at the larynx and pharynx-larynx junction. Generally, droplets' deposition fraction increased with their size, and the maximum size of droplets that were able to escape into external environment decreased with the airflow rate. This threshold size for droplets released from the vocal folds was 10-20 µm, while that for droplets released from the bronchi was 5-20 µm under various airflow rates. Besides, successive syllables pronounced at low airflow rates promoted the escape of small droplets, but do not significantly affect the droplet threshold diameter. This study indicates that droplets larger than 20 µm may entirely originate from the oral cavity, where viral loads are lower; it provides a reference for evaluating the relative importance of large-droplet spray and airborne transmission route of COVID-19 and other respiratory infections.

"Simulation of medical goggles to stop airborne transmission of viruses: computational fluid dynamics in ergonomics"

This paper presents a position statement on combining computational fluid dynamics (CFD) and ergonomics to guide the design of personal protective equipment (PPE). We used CFD to simulate 36 exposure scenarios of an infected patient sneezing at different distances and different angles while facing either the front or the side of a healthcare worker with or without goggles. The results show that medical goggles indeed block most droplets from the outer surface, but many droplets still deposit on the bottom edge (especially at the nose), inside the air holes and on the side edge. However, the edges of medical goggles have fitment problems with people in different regions, and the air holes do not function as filters and cannot prevent fine droplets from entering the interior and contacting the eyes. Our research demonstrates the feasibility of studying the design of PPE for airtightness and protection by means of CFD.Practitioner summary: Computational fluid dynamics can quickly and efficiently reflect the airtightness design problems of PPE. A model was developed using CFD to examine the protective effect of medical goggles in preventing the airborne transmission of viruses. The model demonstrates the feasibility of using CFD to solve ergonomic problems.Abbreviations: CFD: computational fluid dynamics; PPE: personal protective equipment; WHO: the World Health Organisation; COVID-19: coronavirus disease 2019; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; OSHA: the Occupational Safety and Health Administration; CDC: the Centres for Disease Control; FEM: finite element method; 3M: Minnesota Mining and Manufacturing Corporation; SPH: smoothed particle hydrodynamics; AROM: active range of motion; DPM: discrete phase model; PISO: pressure implicit with splitting of operators; VR: virtual reality; AR: augmented reality.

COVID-19: Impact on the Musician and Returning to Singing; A Literature Review

OBJECTIVE

The purpose of this study was to review current literature of the impact of COVID-19 on musicians and returning to singing.

METHODS

A comprehensive search of peer-review articles was completed using PubMed, GoogleScholar, Scopus, and Web of Science. The search was completed using many key terms including voice, hoarseness, dysphonia, aphonia, cough, singers, and public speakers. The bibliography from each article found was searched to find additional articles. The search process revealed 56 peer-reviewed articles, 18 primary articles, ranging from the years 2019 to 2020.

CONCLUSION

COVID-19 has had a major impact on singers and other musicians worldwide. It can affect the voice and can lead to paresis/paralysis of laryngeal nerves to long-term changes in respiratory function. There is a risk from aerosolization/droplet formation transmission with singing, and with playing wind and brass instruments that can be mitigated by following COVID-19 guidelines. Ways to reduce possible transmission during singing and instrument play include virtual rehearsals or performances, mask-wearing, instrument covers, smaller choirs, performing outside, excellent ventilation being socially distanced, shorter rehearsals, regularly cleaning commonly touched surfaces and washing hands, avoiding contact with others, and temperature screening.

Numerical simulation of social distancing of preventing airborne transmission in open space with lateral wind direction, taking into account temperature of human body and floor surface

This paper presents the numerical results of particle propagation in open space, taking into account the temperature of the human body and the surface of the ground. And also, the settling of particles or droplets under the action of gravitational force and transport in the open air is taken into account, taking into account the temperature during the process of breathing and sneezing or coughing. The temperature of the body and the surface of the ground, different rates of particle emission from the mouth, such as breathing and coughing or sneezing, are numerically investigated. The effect of temperature, cross-inlet wind, and the velocity of particle ejection from a person's mouth on social distancing is being investigated using a numerical calculation. The variable temperature of the human body forms a thermal plume, which affects the increase in the trajectory of the particle propagation, taking into account the lateral air flow. The thermal plume affects the particles in the breathing zone and spreads the particles over long distances in the direction of the airflow. The result of this work shows that in open space, taking into account the temperature of the body and the surface of the ground, a 2-m social distance may be insufficient for the process of sneezing and social distance must be observed depending on the breathing mode.

Mechanisms controlling the transport and evaporation of human exhaled respiratory droplets containing the severe acute respiratory syndrome coronavirus: a review

Transmission of the coronavirus disease 2019 is still ongoing despite mass vaccination, lockdowns, and other drastic measures to control the pandemic. This is due partly to our lack of understanding on the multiphase flow mechanics that control droplet transport and viral transmission dynamics. Various models of droplet evaporation have been reported, yet there is still limited knowledge about the influence of physicochemical parameters on the transport of respiratory droplets carrying the severe acute respiratory syndrome coronavirus 2. Here we review the effects of initial droplet size, environmental conditions, virus mutation, and non-volatile components on droplet evaporation and dispersion, and on virus stability. We present experimental and computational methods to analyze droplet transport, and factors controlling transport and evaporation. Methods include thermal manikins, flow techniques, aerosol-generating techniques, nucleic acid-based assays, antibody-based assays, polymerase chain reaction, loop-mediated isothermal amplification, field-effect transistor-based assay, and discrete and gas-phase modeling. Controlling factors include environmental conditions, turbulence, ventilation, ambient temperature, relative humidity, droplet size distribution, non-volatile components, evaporation and mutation. Current results show that medium-sized droplets, e.g., 50 µm, are sensitive to relative humidity. Medium-sized droplets experience delayed evaporation at high relative humidity, and increase airborne lifetime and travel distance. By contrast, at low relative humidity, medium-sized droplets quickly shrink to droplet nuclei and follow the cough jet. Virus inactivation within a few hours generally occurs at temperatures above 40 °C, and the presence of viral particles in aerosols impedes droplet evaporation.

The Spread of Exhaled Air and Aerosols during Physical Exercise

Physical exercise demonstrates a special case of aerosol emission due to its associated elevated breathing rate. This can lead to a faster spread of airborne viruses and respiratory diseases. Therefore, this study investigates cross-infection risk during training. Twelve human subjects exercised on a cycle ergometer under three mask scenarios: no mask, surgical mask, and FFP2 mask. The emitted aerosols were measured in a grey room with a measurement setup equipped with an optical particle sensor. The spread of expired air was qualitatively and quantitatively assessed using schlieren imaging. Moreover, user satisfaction surveys were conducted to evaluate the comfort of wearing face masks during training. The results indicated that both surgical and FFP2 masks significantly reduced particles emission with a reduction efficiency of 87.1% and 91.3% of all particle sizes, respectively. However, compared to surgical masks, FFP2 masks provided a nearly tenfold greater reduction of the particle size range with long residence time in the air (0.3-0.5 μm). Furthermore, the investigated masks reduced exhalation spreading distances to less than 0.15 m and 0.1 m in the case of the surgical mask and FFP2 mask, respectively. User satisfaction solely differed with respect to perceived dyspnea between no mask and FFP2 mask conditions.

Research on the relationship between architectural features in northeast China and vertical aerosol transmission of COVID-19

During the COVID-19 pandemic, many buildings in northeast China have had clusters of infected cases in the vertical layout. There is speculation that vertical aerosol transmission occurs. The houses in northeast China are airtight, and range hoods may be used for a long period of time when cooking. The pathway and factors influencing vertical aerosol transmission are worth studying. To elucidate a viral aerosol transmission pathway, we selected a multistory apartment and a high-rise building in Changchun city, Jilin province, China, to conduct an in-depth investigation and on-site simulation experiments. According to epidemiological investigation information on infected cases, building structures, drainage, ventilation, etc., we used fluorescent microspheres to simulate the behaviors of infected people, such as breathing and flushing the toilet after defecation, to discharge simulated viruses and track and monitor them. The field simulation experiment confirmed the transmission of fluorescent microsphere aerosols to other rooms in two types of buildings using a vertical aerosol transmission pathway of toilet flush-sewage pipe-floor drain without a water seal. Our study showed that, in the absence of a U-shaped trap or floor drain water seal whether in a multistory apartment or high-rise residential building, there is a transmission pathway of "excretion of virus through feces-toilet flushing-sewage pipe-floor drain without water seal," which will cause the vertical transmission of viral aerosol across floors during the COVID-19 pandemic. Moreover, the negative pressure generated by turning on the range hood when closing doors and windows increase aerosol transmission. Based on this negative pressure, prevention and control measures for residential buildings in northeast China during the COVID-19 pandemic were proposed.

Unanswered questions on the airborne transmission of COVID-19

Policies and measures to control pandemics are often failing. While biological factors controlling transmission are usually well explored, little is known about the environmental drivers of transmission and infection. For instance, respiratory droplets and aerosol particles are crucial vectors for the airborne transmission of the severe acute respiratory syndrome coronavirus 2, the causation agent of the coronavirus 2019 pandemic (COVID-19). Once expectorated, respiratory droplets interact with atmospheric particulates that influence the viability and transmission of the novel coronavirus, yet there is little knowledge on this process or its consequences on virus transmission and infection. Here we review the effects of atmospheric particulate properties, vortex zones, and air pollution on virus survivability and transmission. We found that particle size, chemical constituents, electrostatic charges, and the moisture content of airborne particles can have notable effects on virus transmission, with higher survival generally associated with larger particles, yet some viruses are better preserved on small particles. Some chemical constituents and surface-adsorbed chemical species may damage peptide bonds in viral proteins and impair virus stability. Electrostatic charges and water content of atmospheric particulates may affect the adherence of virion particles and possibly their viability. In addition, vortex zones and human thermal plumes are major environmental factors altering the aerodynamics of buoyant particles in air, which can strongly influence the transport of airborne particles and the transmission of associated viruses. Insights into these factors may provide explanations for the widely observed positive correlations between COVID-19 infection and mortality with air pollution, of which particulate matter is a common constituent that may have a central role in the airborne transmission of the novel coronavirus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10311-022-01557-z.

Aerosol measurement identifies SARS-CoV 2 PCR positive adults compared with healthy controls

BACKGROUND

SARS-CoV-2 is spread primarily through droplets and aerosols. Exhaled aerosols are generated in the upper airways through shear stress and in the lung periphery by 'reopening of collapsed airways'. Aerosol measuring may detect highly contagious individuals ("super spreaders or super-emitters") and discriminate between SARS-CoV-2 infected and non-infected individuals. This is the first study comparing exhaled aerosols in SARS-CoV-2 infected individuals and healthy controls.

DESIGN

A prospective observational cohort study in 288 adults, comprising 64 patients testing positive by SARS CoV-2 PCR before enrollment, and 224 healthy adults testing negative (matched control sample) at the University Hospital Frankfurt, Germany, from February to June 2021. Study objective was to evaluate the concentration of exhaled aerosols during physiologic breathing in SARS-CoV-2 PCR-positive and -negative subjects. Secondary outcome measures included correlation of aerosol concentration to SARS-CoV-2 PCR results, change in aerosol concentration due to confounders, and correlation between clinical symptoms and aerosol.

RESULTS

There was a highly significant difference in respiratory aerosol concentrations between SARS-CoV-2 PCR-positive (median 1490.5/L) and -negative subjects (median 252.0/L; p < 0.0001). There were no significant differences due to age, sex, smoking status, or body mass index. ROC analysis showed an AUC of 0.8918.

CONCLUSIONS

Measurements of respiratory aerosols were significantly elevated in SARS-CoV-2 positive individuals, which helps to understand the spread and course of respiratory viral infections, as well as the detection of highly infectious individuals.

How do temperature, humidity, and air saturation state affect the COVID-19 transmission risk?

Environmental parameters have a significant impact on the spread of respiratory viral diseases (temperature (T), relative humidity (RH), and air saturation state). T and RH are strongly correlated with viral inactivation in the air, whereas supersaturated air can promote droplet deposition in the respiratory tract. This study introduces a new concept, the dynamic virus deposition ratio (α), that reflects the dynamic changes in viral inactivation and droplet deposition under varying ambient environments. A non-steady-state-modified Wells-Riley model is established to predict the infection risk of shared air space and highlight the high-risk environmental conditions. Findings reveal that a rise in T would significantly reduce the transmission of COVID-19 in the cold season, while the effect is not significant in the hot season. The infection risk under low-T and high-RH conditions, such as the frozen seafood market, is substantially underestimated, which should be taken seriously. The study encourages selected containment measures against high-risk environmental conditions and cross-discipline management in the public health crisis based on meteorology, government, and medical research.

COVID-19 in non-healthcare workplace settings in NSW, Australia

OBJECTIVES

To describe patterns of SARS-CoV-2 transmission in non-healthcare workplace settings during the first six months of COVID-19 spread, in New South Wales (NSW), Australia.

METHODS

Locally acquired COVID-19 cases between February 2020 and August 2020 were reviewed to determine the: total number of workplace-associated cases and clusters; workplace type; and modes of transmission.

RESULTS

There were 72 COVID-19 workplace clusters with 231 cases and an additional 11 workplace-acquired cases who were not part of a cluster. Workplaces most associated with clusters included construction, manufacture and trade (31%, 22 clusters), office and clerical (25%, 18 clusters) and retail (14%, 10 clusters). Most transmission events were best explained by direct transmission, with two workplace clusters demonstrating evidence of partial indirect spread.

CONCLUSIONS

Findings demonstrate workplace settings, particularly construction, office and retail settings have heightened risk of transmission.

IMPLICATIONS FOR PUBLIC HEALTH

The risk of infectious disease transmission is well understood for healthcare workers, despite other workplace types representing higher volumes of workers with less risk controls. This study should assist policy makers and the public to understand COVID-19 transmission in workplaces and the heightened risks associated with certain workplace settings.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

The Trade-Off between Airborne Pandemic Control and Energy Consumption Using Air Ventilation Solutions

Airborne diseases cause high mortality and adverse socioeconomic consequences. Due to urbanization, more people spend more time indoors. According to recent research, air ventilation reduces long-range airborne transmission in indoor settings. However, air ventilation solutions often incur significant energy costs and ecological footprints. The trade-offs between energy consumption and pandemic control indoors have not yet been thoroughly analyzed. In this work, we use advanced sensors to monitor the energy consumption and pandemic control capabilities of an air-conditioning system, a pedestal fan, and an open window in hospital rooms, classrooms, and conference rooms. A simulation of an indoor airborne pandemic spread of Coronavirus (COVID-19) is used to analyze the Pareto front. For the three examined room types, the Pareto front consists of all three air ventilation solutions, with some ventilation configurations demonstrating significant inefficiencies. Specifically, air-conditioning is found to be efficient only at a very high energy cost and fans seem to pose a reasonable alternative. To conclude, a more informed ventilation policy can bring about a more desirable compromise between energy consumption and pandemic spread control.

Combining Phi6 as a surrogate virus and computational large-eddy simulations to study airborne transmission of SARS-CoV-2 in a restaurant

COVID-19 has highlighted the need for indoor risk-reduction strategies. Our aim is to provide information about the virus dispersion and attempts to reduce the infection risk. Indoor transmission was studied simulating a dining situation in a restaurant. Aerosolized Phi6 viruses were detected with several methods. The aerosol dispersion was modeled by using the Large-Eddy Simulation (LES) technique. Three risk-reduction strategies were studied: (1) augmenting ventilation with air purifiers, (2) spatial partitioning with dividers, and (3) combination of 1 and 2. In all simulations infectious viruses were detected throughout the space proving the existence long-distance aerosol transmission indoors. Experimental cumulative virus numbers and LES dispersion results were qualitatively similar. The LES results were further utilized to derive the evolution of infection probability. Air purifiers augmenting the effective ventilation rate by 65% reduced the spatially averaged infection probability by 30%-32%. This relative reduction manifests with approximately 15 min lag as aerosol dispersion only gradually reaches the purifier units. Both viral findings and LES results confirm that spatial partitioning has a negligible effect on the mean infection-probability indoors, but may affect the local levels adversely. Exploitation of high-resolution LES jointly with microbiological measurements enables an informative interpretation of the experimental results and facilitates a more complete risk assessment.