Possible aerosol transmission of COVID-19 associated with an outbreak in an apartment in Seoul, South Korea, 2020

Controlling the first wave of the COVID-19 pandemic in Malawi: Results from a multi-round study

We investigated behavioral responses to COVID-19 in Malawi, where a first wave of the pandemic occurred between June and August 2020. Contrary to many countries on the African continent, the Government of Malawi did not impose a lockdown or a stay-at-home order in response to the initial spread of SARS-CoV-2. We hypothesized that, in the absence of such requirements to restrict social interactions, individuals would primarily seek to reduce the risk of SARS-CoV-2 transmission during contacts, rather than reduce the extent of their social contacts. We analyzed 4 rounds of a panel survey spanning time periods before, during and after the first wave of the COVID-19 pandemic in Malawi. Five hundred and forty-three participants completed 4 survey interviews between April and November 2020. We found that the likelihood of attending various places and events where individuals work and/or socialize remained largely unchanged during that time. Over the same time frame, however, participants reported adopting on a large scale several behaviors that reduce the transmissibility of SARS-CoV-2 during contacts. The percentage of panel participants who reported practicing physical distancing thus increased from 9.8% to 47.0% in rural areas between April-May 2020 and June-July 2020, and from 11.4% to 59.4% in urban areas. The percentage of respondents who reported wearing a facial mask to prevent the spread of SARS-CoV-2 also increased, reaching 67.7% among rural residents in August-September 2020, and 89.6% among urban residents. The pace at which these behaviors were adopted varied between population groups, with early adopters of mask use more commonly found among more educated office workers, residing in urban areas. The adoption of mask use was also initially slower among women, but later caught up with mask use among men. These findings stress the importance of behavioral changes in containing future SARS-CoV-2 outbreaks in settings where access to vaccination remains low. They also highlight the need for targeted outreach to members of socioeconomic groups in which the adoption of protective behaviors, such as mask use, might be delayed.

Retrospective spatial analysis of cases of COVID-19 in a single military accommodation block corridor, RMAS, January-March 21

Shared ablutions and stairwells, corridor cross-ventilation and non-deliberate perflation (natural draft blowing through a space) are potential risk factors for COVID-19 transmission in corridor-based accommodation. This paper uses retrospective spatial analysis to identify potential built environmental risk factors during the January-March 2021 outbreak in Victory College, Royal Military Academy Sandhurst.Distance was measured in units of single room spacing. Odds, ORs and 95% CIs were calculated to identify and measure associations between distance from exposure and having COVID-19. Distance response trends were assessed using Pearson's χ2 for trend test. Linear relationships were tested using the t-test or rank-sum test.Stairwells and ablutions were not identified as likely sources of infection for all corridor occupants. Assuming occupants used their nearest ablutions, closer distance among those attributed to using ablutions 2 (one of four sets of ablutions), was identified as a risk factor (p=0.05). Testing distance response by χ2 linear trend testing showed a potential association between nearest adjacent positive room and COVID-19 (p=0.06), strongest if dominant air movement along the corridor length was from the left (p=0.10) compared with the right (p=0.24).Formal qualitative spatial analysis and environmental assessment of ventilation and air movement has a role in outbreak investigation in assessing factors related to the built environment. Environmental investigations would best inform outbreak investigations if undertaken contemporaneously. Pre-emptive and retrospective studies can help inform public health advice to military establishments in business continuity planning for isolation facilities, during outbreaks or in future development of the built environment.

Viral infection transmission and indoor air quality: A systematic review

Respiratory disease transmission in indoor environments presents persistent challenges for health authorities, as exemplified by the recent COVID-19 pandemic. This underscores the urgent necessity to investigate the dynamics of viral infection transmission within indoor environments. This systematic review delves into the methodologies of respiratory infection transmission in indoor settings and explores how the quality of indoor air (IAQ) can be controlled to alleviate this risk while considering the imperative of sustainability. Among the 2722 articles reviewed, 178 were retained based on their focus on respiratory viral infection transmission and IAQ. Fifty eight articles delved into SARS-CoV-2 transmission, 21 papers evaluated IAQ in contexts of other pandemics, 53 papers assessed IAQ during the SARS-CoV-2 pandemic, and 46 papers examined control strategies to mitigate infectious transmission. Furthermore, of the 46 papers investigating control strategies, only nine considered energy consumption. These findings highlight clear gaps in current research, such as analyzing indoor air and surface samples for specific indoor environments, oversight of indoor and outdoor parameters (e.g., temperature, relative humidity (RH), and building orientation), neglect of occupancy schedules, and the absence of considerations for energy consumption while enhancing IAQ. This study distinctly identifies the indoor environmental conditions conducive to the thriving of each respiratory virus, offering IAQ trade-offs to mitigate the risk of dominant viruses at any given time. This study argues that future research should involve digital twins in conjunction with machine learning (ML) techniques. This approach aims to enhance IAQ by analyzing the transmission patterns of various respiratory viruses while considering energy consumption.

Reducing Transmission of Airborne Respiratory Pathogens: A New Beginning as the COVID-19 Emergency Ends

BACKGROUND

In response to the COVID-19 pandemic, new evidence-based strategies have emerged for reducing transmission of respiratory infections through management of indoor air.

OBJECTIVES

This paper reviews critical advances that could reduce the burden of disease from inhaled pathogens and describes challenges in their implementation.

DISCUSSION

Proven strategies include assuring sufficient ventilation, air cleaning by filtration, and air disinfection by germicidal ultraviolet (UV) light. Layered intervention strategies are needed to maximize risk reduction. Case studies demonstrate how to implement these tools while also revealing barriers to implementation. Future needs include standards designed with infection resilience and equity in mind, buildings optimized for infection resilience among other drivers, new approaches and technologies to improve ventilation, scientific consensus on the amount of ventilation needed to achieve a desired level of risk, methods for evaluating new air-cleaning technologies, studies of their long-term health effects, workforce training on ventilation systems, easier access to federal funds, demonstration projects in schools, and communication with the public about the importance of indoor air quality and actions people can take to improve it. https://doi.org/10.1289/EHP13878.

The multi-dimensional challenges of controlling respiratory virus transmission in indoor spaces: Insights from the linkage of a microscopic pedestrian simulation and SARS-CoV-2 transmission model

SARS-CoV-2 transmission in indoor spaces, where most infection events occur, depends on the types and duration of human interactions, among others. Understanding how these human behaviours interface with virus characteristics to drive pathogen transmission and dictate the outcomes of non-pharmaceutical interventions is important for the informed and safe use of indoor spaces. To better understand these complex interactions, we developed the Pedestrian Dynamics-Virus Spread model (PeDViS), an individual-based model that combines pedestrian behaviour models with virus spread models incorporating direct and indirect transmission routes. We explored the relationships between virus exposure and the duration, distance, respiratory behaviour, and environment in which interactions between infected and uninfected individuals took place and compared this to benchmark 'at risk' interactions (1.5 metres for 15 minutes). When considering aerosol transmission, individuals adhering to distancing measures may be at risk due to the buildup of airborne virus in the environment when infected individuals spend prolonged time indoors. In our restaurant case, guests seated at tables near infected individuals were at limited risk of infection but could, particularly in poorly ventilated places, experience risks that surpass that of benchmark interactions. Combining interventions that target different transmission routes can aid in accumulating impact, for instance by combining ventilation with face masks. The impact of such combined interventions depends on the relative importance of transmission routes, which is hard to disentangle and highly context dependent. This uncertainty should be considered when assessing transmission risks upon different types of human interactions in indoor spaces. We illustrated the multi-dimensionality of indoor SARS-CoV-2 transmission that emerges from the interplay of human behaviour and the spread of respiratory viruses. A modelling strategy that incorporates this in risk assessments can help inform policy makers and citizens on the safe use of indoor spaces with varying inter-human interactions.

Vertical transmission of infectious aerosols through building toilet drainage system: An experimental study

The building's toilet drainage system has been identified as a potential route for the transmission of SARS-CoV-2 during outbreaks. This study employed agar-fluorescein sodium semi-solid as trace particles to investigate the possibility of vertical transmission of the SARS-CoV-2 in drainage system. In both scenarios, where floor drains were all properly sealed or dried out, simulated faeces containing fluorescein sodium were flushed into the toilet bowl. Air sampling was conducted in each restroom, and differential pressure measurements at the floor drain locations were taken. The experimental results showed that when all floor drains were properly sealed, the differential pressure at each floor drain was 0. The fluorescein sodium-traced aerosol did not transmit through the drainage system to various floors, which significantly reduced the risk of infection for users through this route. However, when all floor drains dried out, toilet users above the neutral pressure layer (NPL) were at a high risk of virus infection. Due to the increasing maximum negative pressure at the floor drain above the NPL with ascending floor levels, users on each floor above the NPL faced an elevated infection risk in restrooms. Specifically, users on the top floor were exposed to infectious aerosols roughly 1.6 times that of the first floor above the NPL. Conversely, owing to the increasing maximum positive pressure at the floor drain below the NPL with descending floor levels, users below the NPL experienced a comparatively lower infection risk. This finding has important implications for understanding the vertical transmission dynamics of SARS-CoV-2 in residential or public building and can inform the development of effective control measures.

Investigation of a COVID-19 cluster involving vertical transmission in a residential building, Taiwan, 2021

We investigated a COVID-19 cluster involved seven case-patients lived in a high-rise building in September 2021. We used a simplified tracer-gas experiment and virus sequencing to establish the link between case-patients. Vertical transmission among vertically aligned apartments on different floors in a building was the most likely route of transmission.

An overview of SARS-CoV-2 transmission and engineering strategies to mitigate risk

The spread of the COVID-19 pandemic has profoundly affected every aspect of our lives. To date, experts have acknowledged that airborne transmission is a key piece of the SARS-CoV-2 puzzle. Nevertheless, the exact mechanism of airborne transmission of SARS-CoV-2 remains unclear. Recent works have shown the spreading of SARS-CoV-2 through numerical modeling and experimental works, but the successful applications of engineering approaches in reducing the spread of SARS-CoV-2 are lacking. In this review, the environmental factors that influence the transmission risk of SARS-CoV-2, such as ventilation flow rates, humidity, and temperature, are discussed. Besides, additional macro and micro weather factors, regional and global transmission, and the variants of the spread of SARS-CoV-2 are also reviewed. Engineering approaches that practically reduce the risks of SARS-CoV-2 transmissions are reported. Given the complex human behavior, environmental properties, and dynamic nature of the SARS-CoV-2 virus, it is reasonable to summarize that SARS-CoV-2 may not be eradicated even with the timely implementation of interventions. Therefore, more research exploring the potential cost-effective ways to control the transmission rate of SARS-CoV-2 may be a worthwhile pursuit to moderate the current crisis.

Probable Evidence of Aerosol Transmission of SARS-COV-2 in a COVID-19 Outbreak of a High-Rise Building

Although it is well established that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be transmitted through aerosols, the mode of long-range aerosol transmission in high-rise buildings remains unclear. In this study, we analyzed an outbreak of coronavirus disease 2019 (COVID-19) that occurred in a high-rise building in China. Our objective was to investigate the plausibility of aerosol transmission of SARS-CoV-2 by testing relevant environmental variables and measuring the dispersion of a tracer gas in the drainage system of the building. The outbreak involved 7 infected families, of which 6 were from vertically aligned flats on different floors. Environmenìtal data revealed that 3 families' bathrooms were contaminated by SARS-CoV-2. In our tracer experiment, we injected tracer gas (CO₂) into the dry floor drains and into water-filled toilets in the index case' s bathroom. Our findings showed that the gas could travel through vertical pipes by the dry floor drains, but not through the water of the toilets. This indicates that dry floor drains might facilitate the transmission of viral aerosols through the sewage system. On the basis of circumstantial evidence, long-range aerosol transmission may have contributed to the community outbreak of COVID-19 in this high-rise building. The vertical transmission of diseases through aerosols in high-rise buildings demands urgent attention.

Investigation of airborne spread of COVID-19 using a hybrid agent-based model: a case study of the UK

Agent-based models have been proven to be quite useful in understanding and predicting the SARS-CoV-2 virus-originated COVID-19 infection. Person-to-person contact was considered as the main mechanism of viral transmission in these models. However, recent understanding has confirmed that airborne transmission is the main route to infection spread of COVID-19. We have developed a computationally efficient agent-based hybrid model to study the aerial propagation of the virus and subsequent spread of infection. We considered virus, a continuous variable, spreads diffusively in air and members of populations as discrete agents possessing one of the eight different states at a particular time. The transition from one state to another is probabilistic and age linked. Recognizing that population movement is a key aspect of infection spread, the model allows unbiased movement of agents. We benchmarked the model to recapture the temporal stochastic infection count data of the UK. The model investigates various key factors such as movement, infection susceptibility, new variants, recovery rate and duration, incubation period and vaccination on the infection propagation over time. Furthermore, the model was applied to capture the infection spread in Italy and France.

A Novel IoT-Enabled Wireless Sensor Grid for Spatial and Temporal Evaluation of Tracer Gas Dispersion

Current IoT applications in indoor air focus mainly on general monitoring. This study proposed a novel IoT application to evaluate airflow patterns and ventilation performance using tracer gas. The tracer gas is a surrogate for small-size particles and bioaerosols and is used in dispersion and ventilation studies. Prevalent commercial tracer-gas-measuring instruments, although highly accurate, are relatively expensive, have a long sampling cycle, and are limited in the number of sampling points. To enhance the spatial and temporal understanding of tracer gas dispersion under the influence of ventilation, a novel application of an IoT-enabled, wireless R134a sensing network using commercially available small sensors was proposed. The system has a detection range of 5-100 ppm and a sampling cycle of 10 s. Using Wi-Fi communication, the measurement data are transmitted to and stored in a cloud database for remote, real-time analysis. The novel system provides a quick response, detailed spatial and temporal profiles of the tracer gas level, and a comparable air change rate analysis. With multiple units deployed as a wireless sensing network, the system can be applied as an affordable alternative to traditional tracer gas systems to identify the dispersion pathway of the tracer gas and the general airflow direction.

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.

Assessment of environmental surface contamination with SARS-CoV-2 in concert halls and banquet rooms in Japan

BACKGROUND

Although crowds are considered to be a risk factor for SARS-CoV-2 transmission, little is known about the changes in environmental surface contamination with the virus when a large number of people attend an event. In this study, we evaluated the changes in environmental surface contamination with SARS-CoV-2.

METHODS

Environmental samples were collected from concert halls and banquet rooms before and after events in February to April 2022 when the 7-day moving average of new COVID-19 cases in Tokyo was reported to be 5000-18000 cases per day. In total, 632 samples were examined for SARS-CoV-2 by quantitative reverse transcription polymerase chain reaction (RT-qPCR) tests, and RT-qPCR-positive samples were subjected to a plaque assay.

RESULTS

The SARS-CoV-2 RNA detection rate before and after the events ranged from 0% to 2.6% versus 0%-5.0% in environmental surface samples, respectively. However, no viable viruses were isolated from all RT-qPCR-positive samples by the plaque assay. There was no significant increase in the environmental surface contamination with SARS-CoV-2 after these events.

CONCLUSIONS

These findings revealed that indirect contact transmission from environmental fomite does not seem to be of great magnitude in a community setting.

Measurement and rapid assessment of indoor air quality at mass gathering events to assess ventilation performance and reduce aerosol transmission of SARS-CoV-2

To assess risk factors for COVID-19 transmission and address the closure of mass gathering events since March 2020, the UK Government ran the Events Research Programme (ERP), following which it reopened live events in sports, music, and culture in July 2021. We report the rapid post-occupancy evaluation of Indoor Air Quality (IAQ) and associated long-range airborne transmission risk conducted in the Environmental Study of the ERP. Ten large venues around the UK were monitored with CO2 sensors at a high spatial and temporal resolution during 90 events. An IAQ Index based on CO2 concentration was developed, and all monitored spaces were classified in bands from A to G based on their average and maximum CO2 concentrations from all events. High resolution monitoring and the IAQ Index depicted the overall state of ventilation at live events, and allowed identification of issues with ventilation effectiveness and distribution, and of spaces with poor ventilation and the settings in which long-range airborne transmission risk may be increased. In numerous settings, CO2 concentrations were found to follow patterns relating to event management and specific occupancy of spaces around the venues. Good ventilation was observed in 90% of spaces monitored for given occupancies. Practical applications: High-resolution monitoring of indoor CO2 concentrations is necessary to detect the spatial variation of indoor air quality (IAQ) in large mass gathering event venues. The paper summarises COVID-19 ventilation guidance for buildings and defines a methodology for measurement and rapid assessment of IAQ during occupancy at live events that can be implemented by venue managers. Comparisons of the CO2 concentrations measured during the events identified the spaces at high risk of long-range transmission of airborne pathogens. Building operators should be mindful of the ventilation strategies used relative to the total occupancy in different spaces and the occupant's activities.

Spread of flushing-generated fecal aerosols in a squat toilet cubicle: Implication for infection risk

Toilet flushing generates and spread fecal aerosols, potentially leading to infection transmission risk. Squat toilets are widely used in public restrooms in some Asian countries including China and India, and remain to be studied. Aerosol dispersion while flushing squat toilet in cubicle was visualized, while the aerosol concentrations were measured on different surfaces by monitoring fluorescence intensity through seeding simulated fluorescence feces. Flushing-generated fecal aerosols could spread to the breathing zone, deposit on floor, and partitions in squat toilet cubicles, and spread even beyond to the restroom lobby. A total of 0.24 % and 0.17 % of seeded fecal waste deposits on the floor and partition (lower than 0.20 m) for each flush. Aerosol concentration decays rapidly, with 86.8 ± 2.2 % reduction in the second minute after a previous flush compared to that in the first minute. Public toilet users are recommended to wait for 2 min after the early flush before entering the cubicle.

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.

The non-linear and interactive effects of meteorological factors on the transmission of COVID-19: A panel smooth transition regression model for cities across the globe

The ongoing pandemic created by COVID-19 has co-existed with humans for some time now, thus resulting in unprecedented disease burden. Previous studies have demonstrated the non-linear and single effects of meteorological factors on viral transmission and have a question of how to exclude the influence of unrelated confounding factors on the relationship. However, the interactions involved in such relationships remain unclear under complex weather conditions. Here, we used a panel smooth transition regression (PSTR) model to investigate the non-linear interactive impact of meteorological factors on daily new cases of COVID-19 based on a panel dataset of 58 global cities observed between Jul 1, 2020 and Jan 13, 2022. This new approach offers a possibility of assessing interactive effects of meteorological factors on daily new cases and uses fixed effects to control other unrelated confounding factors in a panel of cities. Our findings revealed that an optimal temperature range (0°C-20 °C) for the spread of COVID-19. The effect of RH (relative humidity) and DTR (diurnal temperature range) on infection became less positive (coefficient: 0.0427 to -0.0142; p < 0.05) and negative (coefficient: -0.0496 to -0.0248; p < 0.05) with increasing average temperature(T). The highest risk of infection occurred when the temperature was -10 °C and RH was >80% or when the temperature was 10 °C and DTR was 1 °C. Our findings highlight useful implications for policymakers and the general public.

Effects of housing environments on COVID-19 transmission and mental health revealed by COVID-19 Participant Experience data from the All of Us Research Program in the USA: a case-control study

OBJECTIVES

To examine the association between housing types and COVID-19 infection (or mental health) during the early stages of the pandemic by using the large-scale individual-level All of Us Research Program COVID-19 Participant Experience (COPE) survey data. We hypothesise that housing types with a shared component are associated with elevated COVID-19 infection and subsequent mental health conditions.

DESIGN

A retrospective case-control study.

SETTING

Secondary analysis of online surveys conducted in the USA.

PARTICIPANTS

62 664 participant responses to COPE from May to July 2020.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary outcome measure is the self-reported COVID-19 status, and the secondary outcome measures are anxiety or stress. Both measures were applied for matched cases and controls of the same race, sex, age group and survey version.

RESULTS

A multiple logistic regression analysis revealed that housing types with a shared component are significantly associated with COVID-19 infection (OR=1.19, 95% CI 1.1 to 1.3; p=2×10^-4), anxiety (OR=1.26, 95% CI 1.1 to 1.4; p=1.1×10^-6) and stress (OR=1.29, 95% CI 1.2 to 1.4; p=4.3×10^-10) as compared with free-standing houses, after adjusting for confounding factors. Further, frequent optional shopping or outing trips, another indicator of the built environment, are also associated with COVID-19 infection (OR=1.36, 95% CI 1.1 to 1.8; p=0.02), but not associated with elevated mental health conditions. Confounding factors are controlled in the analysis such as ethnicity, age, social distancing behaviour and house occupancy.

CONCLUSION

Our study demonstrates that houses with a shared component tend to have an increased risk of COVID-19 transmission, which consequently leads to high levels of anxiety and stress for their dwellers. The study also suggests the necessity to improve the quality of the built environment such as residential housing and its surroundings through planning, design and management, ensuring a more resilient society that can cope with future pandemics.

Effects of housing environments on COVID-19 transmission and mental health revealed by COVID-19 Participant Experience data from the All of Us Research Program in the USA: a case-control study

OBJECTIVES

To examine the association between housing types and COVID-19 infection (or mental health) during the early stages of the pandemic by using the large-scale individual-level All of Us Research Program COVID-19 Participant Experience (COPE) survey data. We hypothesise that housing types with a shared component are associated with elevated COVID-19 infection and subsequent mental health conditions.

DESIGN

A retrospective case-control study.

SETTING

Secondary analysis of online surveys conducted in the USA.

PARTICIPANTS

62 664 participant responses to COPE from May to July 2020.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary outcome measure is the self-reported COVID-19 status, and the secondary outcome measures are anxiety or stress. Both measures were applied for matched cases and controls of the same race, sex, age group and survey version.

RESULTS

A multiple logistic regression analysis revealed that housing types with a shared component are significantly associated with COVID-19 infection (OR=1.19, 95% CI 1.1 to 1.3; p=2×10^-4), anxiety (OR=1.26, 95% CI 1.1 to 1.4; p=1.1×10^-6) and stress (OR=1.29, 95% CI 1.2 to 1.4; p=4.3×10^-10) as compared with free-standing houses, after adjusting for confounding factors. Further, frequent optional shopping or outing trips, another indicator of the built environment, are also associated with COVID-19 infection (OR=1.36, 95% CI 1.1 to 1.8; p=0.02), but not associated with elevated mental health conditions. Confounding factors are controlled in the analysis such as ethnicity, age, social distancing behaviour and house occupancy.

CONCLUSION

Our study demonstrates that houses with a shared component tend to have an increased risk of COVID-19 transmission, which consequently leads to high levels of anxiety and stress for their dwellers. The study also suggests the necessity to improve the quality of the built environment such as residential housing and its surroundings through planning, design and management, ensuring a more resilient society that can cope with future pandemics.

Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021

We investigated a cluster of SARS-CoV-2 infections in a quarantine hotel in Taiwan in December 2021. The cluster involved 3 case patients who lived in nonadjacent rooms on different floors. They had no direct contact during their stay. By direct exploration of the space above the room ceilings, we found residual tunnels, wall defects, and truncated pipes between their rooms. We conducted a simplified tracer-gas experiment to assess the interconnection between rooms. Aerosol transmission through structural defects in floors and walls in this poorly ventilated hotel was the most likely route of virus transmission. This event demonstrates the high transmissibility of Omicron variants, even across rooms and floors, through structural defects. Our findings emphasize the importance of ventilation and integrity of building structure in quarantine facilities.

What is the role of aerosol transmission in SARS-Cov-2 Omicron spread in Shanghai?

The Omicron transmission has infected nearly 600,000 people in Shanghai from March 26 to May 31, 2022. Combined with different control measures taken by the government in different periods, a dynamic model was constructed to investigate the impact of medical resources, shelter hospitals and aerosol transmission generated by clustered nucleic acid testing on the spread of Omicron. The parameters of the model were estimated by least square method and MCMC method, and the accuracy of the model was verified by the cumulative number of asymptomatic infected persons and confirmed cases in Shanghai from March 26 to May 31, 2022. The result of numerical simulation demonstrated that the aerosol transmission figured prominently in the transmission of Omicron in Shanghai from March 28 to April 30. Without aerosol transmission, the number of asymptomatic subjects and symptomatic cases would be reduced to 130,000 and 11,730 by May 31, respectively. Without the expansion of shelter hospitals in the second phase, the final size of asymptomatic subjects and symptomatic cases might reach 23.2 million and 4.88 million by May 31, respectively. Our results also revealed that expanded vaccination played a vital role in controlling the spread of Omicron. However, even if the vaccination rate were 100%, the transmission of Omicron should not be completely blocked. Therefore, other control measures should be taken to curb the spread of Omicron, such as widespread antiviral therapies, enhanced testing and strict tracking quarantine measures. This perspective could be utilized as a reference for the transmission and prevention of Omicron in other large cities with a population of 10 million like Shanghai.

Polyimide Surface Dielectric Barrier Discharge for Inactivation of SARS-CoV-2 Trapped in a Polypropylene Melt-Blown Filter

Surface dielectric barrier discharge (SDBD) was used to inactivate the infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) trapped in a polypropylene (PP) melt-blown filter. We used a dielectric barrier made of polyimide films with hexagonal holes through which air flowed. In a cylindrical wind tunnel, the SDBD device supplied reactive oxygen species such as ozone to the SARS-CoV-2 trapped in the PP filter. A plaque assay showed that SDBD at an ozone concentration of approximately 51.6 ppm and exposure time of 30 min induced more than 99.78% reduction for filter-adhered SARS-CoV-2. A carbon catalyst after SDBD effectively reduced ozone exhaust below 0.05 ppm. The combination of SDBD, PP filter, and catalyst could be a promising way to decrease the risk of secondary infection due to indoor air purifiers.

High-rise residential building ventilation in cold climates: A review of ventilation system types and their impact on measured building performance

Ventilation system performance in high-rise multi-unit residential buildings (MURBs) has a significant impact on resident wellbeing. While the importance of ventilation is well established, it is commonly overlooked since underperformance often goes undetected. This article presents a review and synthesis of ventilation system performance in high-rise MURBs located in cold climates as it relates to the three pillars of sustainability: economic (capital and operational cost), social (airflow control, indoor environmental quality, and occupant behavior and interactions), and ecological (energy and carbon). A meta-analysis revealed previous ventilation system designs generally prioritized economic sustainability, specifically, capital cost. However, priorities have recently shifted toward social and ecological sustainability. While this shift is positive, there is insufficient empirical evidence showing which ventilation system most effectively supports it. The decentralized heat/energy recovery ventilator (HRV/ERV) system shows the potential to improve upon the social and ecological sustainability of previous designs, such as the centralized pressurized corridor system, but the interconnected nature of performance metrics can cause improvements to one to negatively impact others. Therefore, further research is required to enhance ventilation system performance in cold climate, high-rise MURBs, and facilitate decision-making while designing and retrofitting these systems.

Aerosol transmission of human pathogens: From miasmata to modern viral pandemics and their preservation potential in the Anthropocene record

Ongoing uncertainty over the relative importance of aerosol transmission of COVID-19 is in part rooted in the history of medical science and our understanding of how epidemic diseases can spread through human populations. Ancient Greek medical theory held that such illnesses are transmitted by airborne pathogenic emanations containing particulate matter ("miasmata"). Notable Roman and medieval scholars such as Varro, Ibn al-Khatib and Fracastoro developed these ideas, combining them with early germ theory and the concept of contagion. A widely held but vaguely defined belief in toxic miasmatic mists as a dominant causative agent in disease propagation was overtaken by the science of 19th century microbiology and epidemiology, especially in the study of cholera, which was proven to be mainly transmitted by contaminated water. Airborne disease transmission came to be viewed as burdened by a dubious historical reputation and difficult to demonstrate convincingly. A breakthrough came with the classic mid-20th century work of Wells, Riley and Mills who proved how expiratory aerosols (their "droplet nuclei") could transport still-infectious tuberculosis bacteria through ventilation systems. The topic of aerosol transmission of pathogenic respiratory diseases assumed a new dimension with the mid-late 20th century "Great Acceleration" of an increasingly hypermobile human population repeatedly infected by different strains of zoonotic viruses, and has taken centre stage this century in response to outbreaks of new respiratory infections that include coronaviruses. From a geoscience perspective, the consequences of pandemic-status diseases such as COVID-19, produced by viral pathogens utilising aerosols to infect a human population currently approaching 8 billion, are far-reaching and unprecedented. The obvious and sudden impacts on for example waste plastic production, water and air quality and atmospheric chemistry are accelerating human awareness of current environmental challenges. As such, the "anthropause" lockdown enforced by COVID-19 may come to be seen as a harbinger of change great enough to be preserved in the Anthropocene stratal record.

Ventilation improvement and evaluation of its effectiveness in a Japanese manufacturing factory

A coronavirus disease 2019 (COVID-19) cluster emerged in a manufacturing factory in early August 2021. In November 2021, we conducted a ventilation survey using the tracer gas method. Firstly, we reproduce the situation at the time of cluster emergence and examined whether the ventilation in the office was in a condition that increased the risk of aerosol transmission. Secondly, we verified the effectiveness of the factory's own countermeasure implemented immediately after the August cluster outbreak. Furthermore, we verified the effectiveness of several additional improvement measures on the factory's own countermeasures already installed in August. Under the conditions of the cluster emergence, the air changes per hour (ACH) value was 0.73 ACH on average. The ACH value was less than 2 ACH recommended by the Ministry of Health, Labour, and Welfare, suggesting an increased risk of aerosol transmission. The factory's own countermeasures taken immediately in August were found to be effective, as the ACH value increased to 3.41 ACH on average. Moreover, it was confirmed that additional improvement measures on the factory's own countermeasures increased the ACH value to 8.33 ACH on average. In order to prevent the re-emergence of COVID-19 clusters due to aerosol infection in the office, it was found that while continuing the factory's own countermeasure, additional improvement measures should also be added depending on the number of workers in the room. In a company, it is important that workers themselves continue to take infection control measures autonomously, and confirming the effectiveness of the measures will help maintain workers' motivation. We believe it is helpful that external researchers in multiple fields and internal personnel in charge of the health and safety department and occupational health work together to confirm the effectiveness of conducted measures, such as in this case.

Ventilation reconstruction in bathrooms for restraining hazardous plume: Mitigate COVID-19 and beyond

Converging evidence reports that the probability of vertical transmission patterns via shared drainage systems, may be responsible for the huge contactless community outbreak in high-rise buildings. Publications indicate that a faulty bathroom exhaust fan system is ineffective in removing lifted hazardous virus-laden aerosols from the toilet bowl space. Common strategies (boosting ventilation capability and applying disinfection tablets) seem unsustainable and remain to date untested. Using combined simulation and experimental approaches, we compared three ventilation schemes in a family bathroom including the traditional ceiling fan, floor fan, and side-wall fan. We found that the traditional ceiling fan was barely functional whereby aerosol particles were not being adequately removed. Conversely, a side-wall fan could function efficiently and an enhanced ventilation capability can have increased performance whereby nearly 80.9% of the lifted aerosol particles were removed. There exists a common, and easily-overlooked mistake in the layout of the bathroom, exposing occupants to a contactless vertical pathogen aerosol transmission route. Corrections and dissemination are thus imperative for the reconstruction of these types of family bathrooms. Our findings provide evidence for the bathroom and smart ventilation system upgrade, promoting indoor public health and human hygiene.

Vertical outbreak of COVID-19 in high-rise buildings: The role of sewer stacks and prevention measures

COVID-19 outbreaks in high-rise buildings suggested the transmission route of fecal-aerosol-inhalation due to the involvement of viral aerosols in sewer stacks. The vertical transmission is likely due to the failure of water traps that allow viral aerosols to spread through sewer stacks. This process can be further facilitated by the chimney effect in vent stack, extract ventilation in bathrooms, or wind-induced air pressure fluctuations. To eliminate the risk of such vertical disease spread, the installation of protective devices is highly encouraged in high-rise buildings. Although the mechanism of vertical pathogen spread through drainage pipeline has been illustrated by tracer gas or microbial experiments and numerical modeling, more research is needed to support the update of regulatory and design standards for sewerage facilities.

Sources of SARS-CoV-2 transmission in Jordan: Self-reported approach

Background

Understanding the dynamics of virus transmission is essential for controlling the COVID-19 pandemic. Demographic factors could influence transmission of the virus in different communities. Herein, the sources of COVID-19 infection in Jordan were explored. In addition, the effects of demographic factors and the adherence to preventive measures on household transmission were investigated.

Methods

The study recruited Jordanian adults who recovered from COVID-19 from March to July 2021. Using a questionnaire, information about participants’ demographics, level of adherence to personal protective measures, and their perceived source of COVID-19 infection were collected. Crosstabs were used to test for differences in household transmission ratios between different demographic variables. Logistic regression analysis was used to predict risk factors for household transmission.

Results

The study recruited a total of 2313 participants. Household transmission was the most frequently reported source of infection (44.9%). Other sources of transmission were work/education related (16.0%), friends (8.6%), healthcare facilities (4.8%), social/event gathering (3.1%), shopping activities (2.2%), and public transport (1.6%). Significantly higher ratios of household transmission were reported by older adults (>60 years), college/university students, and female participants. No significant difference in household transmission was found between low-income and medium-high income groups. A significant increase in household transmission ratios was found with increased adherence to mask-wearing and social distancing. This could be a reflection of the reduced risk of community transmission with increased adherence to these preventive measures, coupled with the difficulty in adhering to these measures within the household setting. In multivariate logistic regression, females, young adults (18–30 years), older adults (>60 years), and those who adhere to mask-wearing most of the time were associated with an increased risk of infection in the household setting.

Conclusion

The results reported in the current study provided an insight into the transmission dynamics of the virus in Jordan, as an example of the MENA region. These findings could be invaluable for the future design of public health policies to control COVID-19 and possibly future pandemics.

A Quantitative Risk Estimation Platform for Indoor Aerosol Transmission of COVID-19

Aerosol transmission has played a significant role in the transmission of COVID-19 disease worldwide. We developed a COVID-19 aerosol transmission risk estimation model to better understand how key parameters associated with indoor spaces and infector emissions affect inhaled deposited dose of aerosol particles that convey the SARS-CoV-2 virus. The model calculates the concentration of size-resolved, virus-laden aerosol particles in well-mixed indoor air challenged by emissions from an index case(s). The model uses a mechanistic approach, accounting for particle emission dynamics, particle deposition to indoor surfaces, ventilation rate, and single-zone filtration. The novelty of this model relates to the concept of "inhaled & deposited dose" in the respiratory system of receptors linked to a dose-response curve for human coronavirus HCoV-229E. We estimated the volume of inhaled & deposited dose of particles in the 0.5-4 μm range expressed in picoliters (pL) in a well-documented COVID-19 outbreak in restaurant X in Guangzhou China. We anchored the attack rate with the dose-response curve of HCoV-229E which provides a preliminary estimate of the average SARS-CoV-2 dose per person, expressed in plaque forming units (PFUs). For a reasonable emission scenario, we estimate approximately three PFU per pL deposited, yielding roughly 10 PFUs deposited in the respiratory system of those infected in restaurant X. To explore the model's utility, we tested it with four COVID-19 outbreaks. The risk estimates from the model fit reasonably well with the reported number of confirmed cases given available metadata from the outbreaks and uncertainties associated with model assumptions.

Elucidating the role of environmental management of forests, air quality, solid waste and wastewater on the dissemination of SARS-CoV-2

The increasing frequency of zoonotic diseases is amongst several catastrophic repercussions of inadequate environmental management. Emergence, prevalence, and lethality of zoonotic diseases is intrinsically linked to environmental management which are currently at a destructive level globally. The effects of these links are complicated and interdependent, creating an urgent need of elucidating the role of environmental mismanagement to improve our resilience to future pandemics. This review focused on the pertinent role of forests, outdoor air, indoor air, solid waste and wastewater management in COVID-19 dissemination to analyze the opportunities prevailing to control infectious diseases considering relevant data from previous disease outbreaks. Global forest management is currently detrimental and hotspots of forest fragmentation have demonstrated to result in zoonotic disease emergences. Deforestation is reported to increase susceptibility to COVID-19 due to wildfire induced pollution and loss of forest ecosystem services. Detection of SARS-CoV-2 like viruses in multiple animal species also point to the impacts of biodiversity loss and forest fragmentation in relation to COVID-19. Available literature on air quality and COVID-19 have provided insights into the potential of air pollutants acting as plausible virus carrier and aggravating immune responses and expression of ACE2 receptors. SARS-CoV-2 is detected in outdoor air, indoor air, solid waste, wastewater and shown to prevail on solid surfaces and aerosols for prolonged hours. Furthermore, lack of protection measures and safe disposal options in waste management are evoking concerns especially in underdeveloped countries due to high infectivity of SARS-CoV-2. Inadequate legal framework and non-adherence to environmental regulations were observed to aggravate the postulated risks and vulnerability to future waves of pandemics. Our understanding underlines the urgent need to reinforce the fragile status of global environmental management systems through the development of strict legislative frameworks and enforcement by providing institutional, financial and technical supports.

Analysis of COVID-19 clusters involving vertical transmission in residential buildings in Hong Kong

Multiple clusters of coronavirus disease 2019 (COVID-19) in Hong Kong have involved vertical transmissions in residential buildings, wherein the flats of confirmed cases were often vertically aligned. Data on the buildings and cases associated with 19 such clusters were retrieved and compared with the corresponding data on the entirety of Hong Kong. Vertical transmissions usually occurred in old high-rise buildings with small flat areas and low estate prices during winter. In addition, infection occurred frequently among the elderly and among upstairs neighbours of index cases. Virus-laden aerosols may have been transmitted between flats mostly via shared drainpipes, and the vertical distribution of the confirmed cases in a building varied by its drainage system design. For buildings with their entire drainpipes installed indoors, both the upstairs and downstairs neighbours of the index case flats could be infected. By comparison, buildings with their drainage stacks installed outdoors had lower infection risks and demonstrated a clearer pattern of vertical transmission: most infected cases resided upstairs from the index case flats, indicating that the virus spread could be dominated by the stack effect. This study provides valuable data and analysis for developing epidemic control strategies for residential buildings.

ELECTRONIC SUPPLEMENTARY MATERIAL ESM

The Appendix is available in the online version of this article at 10.1007/s12273-022-0929-5.

In-duct grating-like dielectric barrier discharge system for air disinfection

In the context of spreading Coronavirus disease 2019 (COVID-19), the combination of heating, ventilation, and air-conditioning (HVAC) system with air disinfection device is an effective way to reduce transmissible infections. Atmospheric-pressure non-equilibrium plasma is an emerging technique for fast pathogen aerosol abatement. In this work, in-duct disinfectors based on grating-like dielectric barrier discharge (DBD) plasmas with varied electrode arrangements were established and evaluated. The highest airborne bacterial inactivation efficiency was achieved by 'vertical' structure, namely when aerosol was in direct contact with the discharge region, at a given discharge power. For all reactors, the efficiency was linearly correlated to the discharge power (R² =0.929-0.994). The effects of environmental factors were examined. Decreased airflow rates boosted the efficiency, which reached 99.8% at the velocity of 0.5 m/s with an aerosol residence time of ~3.6 ms. Increasing humidity (relative humidity (RH)=20-60%) contributed to inactivation efficacy, while high humidity (RH=70%-90%) led to a saturated efficiency, possibly due to the disruption of discharge uniformity. As suggested by the plasma effluent treatment and scavenger experiments, gaseous short-lived chemical species or charged particles were concluded as the major agents accounting for bacterial inactivation. This research provides new hints for air disinfection by DBD plasmas.

Explosive outbreak of SARS-CoV-2 Omicron variant is associated with vertical transmission in high-rise residential buildings in Hong Kong

The phenomenon of vertical transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in high-rise residential buildings (HRRBs) is unique in our densely populated cosmopolitan city. The compulsory testing of a whole building under the scheme of restriction-testing declaration (RTD) during the fourth wave (non-Omicron variant) and fifth wave (mostly Omicron variant) of COVID-19 outbreak in Hong Kong allowed us to study the prevalence of this phenomenon, which may represent a form of airborne transmission. From 23 January 2021 to 24 March 2022, 25,450 (5.8%) of 436,397 residents from 223 (63.0%) of 354 HRRBs under RTD were test-positive for SARS-CoV-2. Using the clustering of cases among vertically aligned flats with shared drainage stack and lightwell as a surrogate marker of vertical transmission, the number of vertically aligned flats with positive COVID-19 cases was significantly higher in the fifth wave compared with the fourth wave (14.2%, 6471/45,531 vs 0.24%, 3/1272; p < 0.001; or 2212 vs 1 per-million-flats; p < 0.001). Excluding 22,801 residents from 38 HRRBs who were tested negative outside the 12-week periods selected in fourth and fifth waves, the positive rate among residents was significantly higher among residents during the fifth wave than the fourth wave (6.5%, 25,434/389,700 vs 0.07%, 16/23,896; p < 0.001). Within the flats with COVID-19 cases, the proportion of vertically aligned flats was also significantly higher in the fifth wave than in the fourth wave (95.6%, 6471/6766 vs 30.0%, 3/10, p < 0.001). The proportion of HRRBs with COVID-19 cases was significantly higher during the corresponding 12-week period chosen for comparison (78.2%, 219/280 vs 11.1%, 4/36; p < 0.001). Whole-genome phylogenetic analysis of 332 viral genomes showed that Omicron BA.2 was the predominant strain, supporting the high transmissibility of BA.2 by airborne excreta-aerosol route in HRRBs of Hong Kong.

Role of ventilation on the transmission of viruses in buildings, from a single zone to a multizone approach

In a virus pandemic context, buildings ventilation has been recognized as a solution for preventing transmission of the virus in aerosolized form. The impact of the widespread recommendation of window opening and sealing door on ventilation circuits needs to be considered with a multizone approach. We modeled the airflow distribution in a building where people are isolating in a pandemic context, including one infected person. We analyzed the impact of opening the window and sealing the door in the quarantine room on exposures and probability of infection for occupants of the flat and of adjacent flats. In order to study the sensitivity of the results, we tested three ventilation systems: balanced, exhaust-only, and humidity-based demand-controlled, and several window- and door-opening strategies. When the door of the quarantine room is sealed, we observe that opening the window in the quarantine room always results in increased exposure and probability of infection for at least one other occupant, including in neighbors' apartments. When all internal doors are opened, we observe moderate impacts, with rather an increase of exposure of the occupants of the same apartments and of their probability of infection, and a decrease for the occupants located in other apartments. Based on the analysis on the airflows distribution in this case study, we conclude that sealing the internal door has more influence than opening the window of the quarantine room, whatever the ventilation system. We observe that this widespread recommendation to open the window of a quarantine room and to seal the door is based on the consideration of a single zone model. We illustrate the importance of moving from such a single zone approach to a multizone approach for quantifying ventilation and airing impacts in multizone buildings as residences in order to prevent epidemics of viruses such as SARS-CoV-2. It highlights the need of air leakage databases.

SARS-CoV-2 Surveillance in Indoor Air Using Electrochemical Sensor for Continuous Monitoring and Real-Time Alerts

The severe acute respiratory syndrome related coronavirus 2 (SARS-CoV-2) has spread globally and there is still a lack of rapid detection techniques for SARS-CoV-2 surveillance in indoor air. In this work, two test rigs were developed that enable continuous air monitoring for the detection of SARS-CoV-2 by sample collection and testing. The collected samples from simulated SARS-CoV-2 contaminated air were analyzed using an ultra-fast COVID-19 diagnostic sensor (UFC-19). The test rigs utilized two air sampling methods: cyclone-based collection and internal impaction. The former achieved a limit of detection (LoD) of 0.004 cp/L in the air (which translates to 0.5 cp/mL when tested in aqueous solution), lower than the latter with a limit of 0.029 cp/L in the air. The LoD of 0.5 cp/mL using the UFC-19 sensor in aqueous solution is significantly lower than the best-in-class assays (100 cp/mL) and FDA EUA RT-PCR test (6250 cp/mL). In addition, the developed test rig provides an ultra-fast method to detect airborne SARS-CoV-2. The required time to test 250 L air is less than 5 min. While most of the time is consumed by the air collection process, the sensing is completed in less than 2 s using the UFC-19 sensor. This method is much faster than both the rapid antigen (<20 min) and RT-PCR test (<90 min).

Long distance airborne transmission of SARS-CoV-2: rapid systematic review

OBJECTIVES

To evaluate the potential for long distance airborne transmission of SARS-CoV-2 in indoor community settings and to investigate factors that might influence transmission.

DESIGN

Rapid systematic review and narrative synthesis.

DATA SOURCES

Medline, Embase, medRxiv, Arxiv, and WHO COVID-19 Research Database for studies published from 27 July 2020 to 19 January 2022; existing relevant rapid systematic review for studies published from 1 January 2020 to 27 July 2020; and citation analysis in Web of Science and Cocites.

ELIGIBILITY CRITERIA FOR STUDY SELECTION

Observational studies reporting on transmission events in indoor community (non-healthcare) settings in which long distance airborne transmission of SARS-CoV-2 was the most likely route. Studies such as those of household transmission where the main transmission route was likely to be close contact or fomite transmission were excluded.

DATA EXTRACTION AND SYNTHESIS

Data extraction was done by one reviewer and independently checked by a second reviewer. Primary outcomes were SARS-CoV-2 infections through long distance airborne transmission (>2 m) and any modifying factors. Methodological quality of included studies was rated using the quality criteria checklist, and certainty of primary outcomes was determined using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) framework. Narrative synthesis was themed by setting.

RESULTS

22 reports relating to 18 studies were identified (methodological quality was high in three, medium in five, and low in 10); all the studies were outbreak investigations. Long distance airborne transmission was likely to have occurred for some or all transmission events in 16 studies and was unclear in two studies (GRADE: very low certainty). In the 16 studies, one or more factors plausibly increased the likelihood of long distance airborne transmission, particularly insufficient air replacement (very low certainty), directional air flow (very low certainty), and activities associated with increased emission of aerosols, such as singing or speaking loudly (very low certainty). In 13 studies, the primary cases were reported as being asymptomatic, presymptomatic, or around symptom onset at the time of transmission. Although some of the included studies were well conducted outbreak investigations, they remain at risk of bias owing to study design and do not always provide the level of detail needed to fully assess transmission routes.

CONCLUSION

This rapid systematic review found evidence suggesting that long distance airborne transmission of SARS-CoV-2 might occur in indoor settings such as restaurants, workplaces, and venues for choirs, and identified factors such as insufficient air replacement that probably contributed to transmission. These results strengthen the need for mitigation measures in indoor settings, particularly the use of adequate ventilation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021236762.

Enhanced decay of coronaviruses in sewers with domestic wastewater

Recent outbreaks caused by coronaviruses and their supposed potential fecal-oral transmission highlight the need for understanding the survival of infectious coronavirus in domestic sewers. To date, the survivability and decay of coronaviruses were predominately studied using small volumes of wastewater (normally 5-30 mL) in vials (in-vial tests). However, real sewers are more complicated than bulk wastewater (wastewater matrix only), in particular the presence of sewer biofilms and different operational conditions. This study investigated the decay of infectious human coronavirus 229E (HCoV-229E) and feline infectious peritonitis virus (FIPV), two typical surrogate coronaviruses, in laboratory-scale reactors mimicking the gravity (GS, gravity-driven sewers) and rising main sewers (RM, pressurized sewers) with and without sewer biofilms. The in-sewer decay of both coronaviruses was greatly enhanced in comparison to those reported in bulk wastewater through in-vial tests. 99% of HCoV-229E and FIPV decayed within 2 h under either GS or RM conditions with biofilms, in contrast to 6-10 h without biofilms. There is limited difference in the decay of HCoV and FIPV in reactors operated as RM or GS, with the T90 and T99 difference of 7-10 min and 14-20 min, respectively. The decay of both coronaviruses in sewer biofilm reactors can be simulated by biphasic first-order kinetic models, with the first-order rate constant 2-4 times higher during the first phase than the second phase. The decay of infectious HCoV and FIPV was significantly faster in the reactors with sewer biofilms than in the reactors without biofilms, suggesting an enhanced decay of these surrogate viruses due to the presence of biofilms and related processes. The mechanism of biofilms in virus adsorption and potential inactivation remains unclear and requires future investigations. The results indicate that the survivability of infectious coronaviruses detected using bulk wastewater overestimated the infectivity risk of coronavirus during wastewater transportations in sewers or the downstream treatment.

Direct capture and smartphone quantification of airborne SARS-CoV-2 on a paper microfluidic chip

SARS, a new type of respiratory disease caused by SARS-CoV, was identified in 2003 with significant levels of morbidity and mortality. The recent pandemic of COVID-19, caused by SARS-CoV-2, has generated even greater extents of morbidity and mortality across the entire world. Both SARS-CoV and SARS-CoV-2 spreads through the air in the form of droplets and potentially smaller droplets (aerosols) via exhaling, coughing, and sneezing. Direct detection from such airborne droplets would be ideal for protecting general public from potential exposure before they infect individuals. However, the number of viruses in such droplets and aerosols is too low to be detected directly. A separate air sampler and enough collection time (several hours) are necessary to capture a sufficient number of viruses. In this work, we have demonstrated the direct capture of the airborne droplets on the paper microfluidic chip without the need for any other equipment. 10% human saliva samples were spiked with the known concentration of SARS-CoV-2 and sprayed to generate liquid droplets and aerosols into the air. Antibody-conjugated submicron particle suspension is then added to the paper channel, and a smartphone-based fluorescence microscope isolated and counted the immunoagglutinated particles on the paper chip. The total capture-to-assay time was <30 min, compared to several hours with the other methods. In this manner, SARS-CoV-2 could be detected directly from the air in a handheld and low-cost manner, contributing to slowing the spread of SARS-CoV-2. We can presumably adapt this technology to a wide range of other respiratory viruses.

SARS-CoV-2 aerosol transmission and detection

Aerosol transmission has been officially recognized by the world health authority resulting from its overwhelming experimental and epidemiological evidences. Despite substantial progress, few additional actions were taken to prevent aerosol transmission, and many key scientific questions still await urgent investigations. The grand challenge, the effective control of aerosol transmission of COVID-19, remains unsolved. A better understanding of the viral shedding into the air has been developed, but its temporal pattern is largely unknown. Sampling tools, as one of the critical elements for studying SARS-CoV-2 aerosol, are not readily available around the world. Many of them are less capable of preserving the viability of SARS-CoV-2, thus offering no clues about viral aerosol infectivity. As evidenced, the viability of SARS-CoV-2 is also directly impacted by temperature, humidity, sunlight, and air pollutants. For SARS-CoV-2 aerosol detection, liquid samplers, together with real-time polymerase chain reaction (RT-PCR), are currently used in certain enclosed or semi-enclosed environments. Sensitive and rapid COVID-19 screening technologies are in great need. Among others, the breath-borne-based method emerges with global attention due to its advantages in sample collection and early disease detection. To collectively confront these challenges, scientists from different fields around the world need to fight together for the welfare of mankind. This review summarized the current understanding of the aerosol transmission of SARS-CoV-2 and identified the key knowledge gaps with a to-do list. This review also serves as a call for efforts to develop technologies to better protect the people in a forthcoming reopening world.

The Perception of the Vertical Dimension (3D) through the Lens of Different Stakeholders in the Property Market of China

China has experienced fast urbanization with a growing urban population, which has inevitably led to the adoption of a vertical housing style with high-rise buildings. However, how people subjectively perceive the vertical dimension (3D) in the property market is neither adequately documented nor well understood. The 3D perception helps us to understand a myriad of social and psychological effects of living in high-rise buildings. We organized and conducted semi-structured expert interviews, focus groups, and the circulation and compilation of questionnaires in Xi’an, China, to investigate how different stakeholders in the property market perceive 3D. The results show that: (1) real estate developers do not adjust property prices for specific 3D factors, and the local government does not consider 3D in housing policies; (2) the current status of 3D modeling in Xi’an is still in the embryonic state; (3) 3D factors are highly valued by buyers but not well-understood by real estate developers and local government. In addition, 3D factors score higher than horizontal (2D) factors (by 1.12 to 0.88). Gender and age groups do not influence housing preferences concerning 2D and 3D factors. These findings provide valuable insights for real estate developers concerning pricing policies and the local government concerning housing policies. In the future, 3D perceptions and factors should be prioritized in order to improve urban infrastructure and ensure the increased availability of, and fair public access to welfare related to 3D in urban areas.

A missing layer in COVID-19 studies: Transmission of enveloped viruses in mucus-rich droplets

Here we evaluate the influence of mucus layers on the evaporation time and transport of enveloped viruses, including SARS-CoV-2. Enveloped viruses must remain moist to be fully infective. Yet, the Wells model based on water droplets divides respiratory droplets into either quickly evaporated aerosolized particles termed droplet nuclei (<10 s) or liquid droplets that fall to the nearest surface, leaving no physical mechanism for airborne transmission of fully infective enveloped viruses over large distances (greater than a few meters). Yet, the role of mucus layers on evaporation times has not been considered even though the formation of mucus shells around liquid cores of respiratory droplets has been shown experimentally. Here we show that mucus shells increase the drying time by orders of magnitude so that enveloped virions may remain well hydrated and, thus, fully infective at substantial distances. This provides a mechanism by which infective enveloped virus particles can transmit as aerosols within buildings and between buildings over extended distances. This analysis is important because public health agencies typically follow the Wells model to establish health policies including social/physical distancing guidelines.

Biosensor detection of airborne respiratory viruses such as SARS-CoV-2

Airborne SARS-CoV-2 transmission represents a significant route for possible human infection that is not yet fully understood. Viruses in droplets and aerosols are difficult to detect because they are typically present in low amounts. In addition, the current techniques used, such as RT-PCR and virus culturing, require large amounts of time to get results. Biosensor technology can provide rapid, handheld, and point-of-care systems that can identify virus presence quickly and accurately. This paper reviews the background of airborne virus transmission and the characteristics of SARS-CoV-2, its relative risk for transmission even at distances greater than the currently suggested 6 feet (or 2 m) physical distancing. Publications on biosensor technology that may be applied to the detection of airborne SARS-CoV-2 and other respiratory viruses are also summarized. Based on the current research we believe that there is a pressing need for continued research into handheld and rapid methods for sensitive collection and detection of airborne viruses. We propose a paper-based microfluidic chip and immunofluorescence assay as one method that could be investigated as a low-cost and portable option.

Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (H_r) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (H_r) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

COVID-19 Cluster Linked to Aerosol Transmission of SARS-CoV-2 via Floor Drains

BACKGROUND

Recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission through exposure to aerosols has been suggested. Therefore, we investigated the possibility of aerosol SARS-CoV-2 transmission within an apartment complex where residents reported testing positive for SARS-CoV-2 despite having no direct contact with other SARS-CoV-2-infected people.

METHODS

Information on symptom onset and exposure history of the patients was collected by global positioning system (GPS) tracking to investigate possible points of contact or spread. Samples collected from patients and from various areas of the complex were analyzed using RNA sequencing. Phylogenetic analysis was also performed.

RESULTS

Of 19 people with confirmed SARS-CoV-2 infection, 5 reported no direct contact with other residents and were from apartments in the same vertical line. Eight environmental samples tested positive for the virus. Phylogenetic analyses revealed that 3 of the positive cases and 1 environmental sample belonged to the B.1.497 lineage. Additionally, 3 clinical specimens and 1 environmental sample from each floor of the complex had the same amino acid substitution in the ORF1ab region.

CONCLUSIONS

SARS-CoV-2 transmission possibly occurs between different floors of an apartment building through aerosol transmission via nonfunctioning drain traps.

Indoor aerosol science aspects of SARS-CoV-2 transmission

Knowledge about person-to-person transmission of SARS-CoV-2 is reviewed, emphasizing three components: emission of virus-containing particles and drops from infectious persons; transport and fate of such emissions indoors; and inhalation of viral particles by susceptible persons. Emissions are usefully clustered into three groups: small particles (diameter 0.1-5 µm), large particles (5-100 µm), and ballistic drops (>100 µm). Speaking generates particles and drops across the size spectrum. Small particles are removed from indoor air at room scale by ventilation, filtration, and deposition; large particles mainly deposit onto indoor surfaces. Proximate exposure enhancements are associated with large particles with contributions from ballistic drops. Masking and social distancing are effective in mitigating transmission from proximate exposures. At room scale, masking, ventilation, and filtration can contribute to limit exposures. Important information gaps prevent a quantitative reconciliation of the high overall global spread of COVID-19 with known transmission pathways. Available information supports several findings with moderate-to-high confidence: transmission occurs predominantly indoors; inhalation of airborne particles (up to 50 µm in diameter) contributes substantially to viral spread; transmission occurs in near proximity and at room scale; speaking is a major source of airborne SARS-CoV-2 virus; and emissions can occur without strong illness symptoms.

Prediction and control of aerosol transmission of SARS-CoV-2 in ventilated context: from source to receptor

Global spread of COVID-19 has seriously threatened human life and health. The aerosol transmission route of SARS-CoV-2 is observed often associated with infection clusters under poorly ventilated environment. In the context of COVID-19 pandemic, significant transformation and optimization of traditional ventilation systems are needed. This paper is aimed to offer better understanding and insights into effective ventilation design to maximize its ability in airborne risk control, for particularly the COVID-19. Comprehensive reviews of each phase of aerosol transmission of SARS-CoV-2 from source to receptor are conducted, so as to provide a theoretical basis for risk prediction and control. Infection risk models and their key parameters for risk assessment of SARS-CoV-2 are analyzed. Special focus is given on the efficacy of different ventilation strategies in mitigating airborne transmission. Ventilation interventions are found mainly impacting on the dispersion and inhalation phases of aerosol transmission. The airflow patterns become a key factor in controlling the aerosol diffusion and distribution. Novel and personalized ventilation design, effective integration with other environmental control techniques and resilient HVAC system design to adapt both common and epidemic conditions are still remaining challenging, which need to be solved with the aid of multidisciplinary research and intelligent technologies.

Hypothesis: All respiratory viruses (including SARS-CoV-2) are aerosol-transmitted

The potential role of aerosol transmission for seasonal respiratory viruses has been dramatically highlighted during the ongoing COVID-19 pandemic. It is now evident that short-range (conversational) and long-range aerosol transmission plays at least some part in how all these respiratory viruses are transmitted between people. This article highlights and discusses various studies that form the basis for this hypothesis.

SARS-CoV-2 in residential rooms of two self-isolating persons with COVID-19

Individuals with COVID-19 are advised to self-isolate at their residences unless they require hospitalization. Persons sharing a dwelling with someone who has COVID-19 have a substantial risk of being exposed to the virus. However, environmental monitoring for the detection of virus in such settings is limited. We present a pilot study on environmental sampling for SARS-CoV-2 virions in the residential rooms of two volunteers with COVID-19 who self-quarantined. Apart from standard surface swab sampling, based on availability, four air samplers positioned 0.3-2.2 m from the volunteers were used: a VIable Virus Aerosol Sampler (VIVAS), an inline air sampler that traps particles on polytetrafluoroethylene (PTFE) filters, a NIOSH 2-stage cyclone sampler (BC-251), and a Sioutas personal cascade impactor sampler (PCIS). The latter two selectively collect particles of specific size ranges. SARS-CoV-2 RNA was detected by real-time Reverse-Transcription quantitative Polymerase Chain Reaction (rRT-qPCR) analyses of particles in one air sample from the room of volunteer A and in various air and surface samples from that of volunteer B. The one positive sample collected by the NIOSH sampler from volunteer A's room had a quantitation cycle (Cq) of 38.21 for the N-gene, indicating a low amount of airborne virus [5.69E-02 SARS-CoV-2 genome equivalents (GE)/cm3 of air]. In contrast, air samples and surface samples collected off the mobile phone in volunteer B's room yielded Cq values ranging from 14.58 to 24.73 and 21.01 to 24.74, respectively, on the first day of sampling, indicating that this volunteer was actively shedding relatively high amounts of SARS-CoV-2 at that time. The SARS-CoV-2 GE/cm3 of air for the air samples collected by the PCIS was in the range 6.84E+04 to 3.04E+05 using the LED-N primer system, the highest being from the stage 4 filter, and similarly, ranged from 2.54E+03 to 1.68E+05 GE/cm3 in air collected by the NIOSH sampler. Attempts to isolate the virus in cell culture from the samples from volunteer B's room with the aforementioned Cq values were unsuccessful due to out-competition by a co-infecting Human adenovirus B3 (HAdVB3) that killed the Vero E6 cell cultures within 4 days of their inoculation, although Cq values of 34.56-37.32 were measured upon rRT-qPCR analyses of vRNA purified from the cell culture medium. The size distribution of SARS-CoV-2-laden aerosol particles collected from the air of volunteer B's room was >0.25 μm and >0.1 μm as recorded by the PCIS and the NIOSH sampler, respectively, suggesting a risk of aerosol transmission since these particles can remain suspended in air for an extended time and travel over long distances. The detection of virus in surface samples also underscores the potential for fomite transmission of SARS-CoV-2 in indoor settings.