Exhaled aerosol increases with COVID-19 infection, age, and obesity

Host behaviour driven by awareness of infection risk amplifies the chance of superspreading events

We demonstrate that heterogeneity in the perceived risks associated with infection within host populations amplifies chances of superspreading during the crucial early stages of epidemics. Under this behavioural model, individuals less concerned about dangers from infection are more likely to be infected and attend larger sized (riskier) events, where we assume event sizes remain unchanged. For directly transmitted diseases such as COVID-19, this leads to infections being introduced at rates above the population prevalence to those events most conducive to superspreading. We develop an interpretable, computational framework for evaluating within-event risks and derive a small-scale reproduction number measuring how the infections generated at an event depend on transmission heterogeneities and numbers of introductions. This generalizes previous frameworks and quantifies how event-scale patterns and population-level characteristics relate. As event duration and size grow, our reproduction number converges to the basic reproduction number. We illustrate that even moderate levels of heterogeneity in the perceived risks of infection substantially increase the likelihood of disproportionately large clusters of infections occurring at larger events, despite fixed overall disease prevalence. We show why collecting data linking host behaviour and event attendance is essential for accurately assessing the risks posed by invading pathogens in emerging stages of outbreaks.

A COVID-19 cluster analysis in an office: Assessing the long-range aerosol and fomite transmissions with infection control measures

Simulated exposure to severe acute respiratory syndrome coronavirus 2 in the environment was demonstrated based on the actual coronavirus disease 2019 cluster occurrence in an office, with a projected risk considering the likely transmission pathways via aerosols and fomites. A total of 35/85 occupants were infected, with the attack rate in the first stage as 0.30. It was inferred that the aerosol transmission at long-range produced the cluster at virus concentration in the saliva of the infected cases on the basis of the simulation, more than 108 PFU mL-1. Additionally, all wearing masks effectiveness was estimated to be 61%-81% and 88%-95% reduction in risk for long-range aerosol transmission in the normal and fit state of the masks, respectively, and a 99.8% or above decline in risk of fomite transmission. The ventilation effectiveness for long-range aerosol transmission was also calculated to be 12%-29% and 36%-66% reductions with increases from one air change per hour (ACH) to two ACH and six ACH, respectively. Furthermore, the virus concentration reduction in the saliva to 1/3 corresponded to the risk reduction for long-range aerosol transmission by 60%-64% and 40%-51% with and without masks, respectively.

Particles in Exhaled Air (PExA): Clinical Uses and Future Implications

Access to distal airway samples to assess respiratory diseases is not straightforward and requires invasive procedures such as bronchoscopy and bronchoalveolar lavage. The particles in exhaled air (PExA) device provides a non-invasive means of assessing small airways; it captures distal airway particles (PEx) sized around 0.5-7 μm and contains particles of respiratory tract lining fluid (RTLF) that originate during airway closure and opening. The PExA device can count particles and measure particle mass according to their size. The PEx particles can be analysed for metabolites on various analytical platforms to quantitatively measure targeted and untargeted lung specific markers of inflammation. As such, the measurement of distal airway components may help to evaluate acute and chronic inflammatory conditions such as asthma, chronic obstructive pulmonary disease, acute respiratory distress syndrome, and more recently, acute viral infections such as COVID-19. PExA may provide an alternative to traditional methods of airway sampling, such as induced sputum, tracheal aspirate, or bronchoalveolar lavage. The measurement of specific biomarkers of airway inflammation obtained directly from the RTLF by PExA enables a more accurate and comprehensive understanding of pathophysiological changes at the molecular level in patients with acute and chronic lung diseases.

Building Environmental and Sociological Predictive Intelligence to Understand the Seasonal Threat of SARS-CoV-2 in Human Populations

Current modeling practices for environmental and sociological modulated infectious diseases remain inadequate to forecast the risk of outbreak(s) in human populations, partly due to a lack of integration of disciplinary knowledge, limited availability of disease surveillance datasets, and overreliance on compartmental epidemiological modeling methods. Harvesting data knowledge from virus transmission (aerosols) and detection (wastewater) of SARS-CoV-2, a heuristic score-based environmental predictive intelligence system was developed that calculates the risk of COVID-19 in the human population. Seasonal validation of the algorithm was uniquely associated with wastewater surveillance of the virus, providing a lead time of 7-14 days before a county-level outbreak. Using county-scale disease prevalence data from the United States, the algorithm could predict COVID-19 risk with an overall accuracy ranging between 81% and 98%. Similarly, using wastewater surveillance data from Illinois and Maryland, the SARS-CoV-2 detection rate was greater than 80% for 75% of the locations during the same time the risk was predicted to be high. Results suggest the importance of a holistic approach across disciplinary boundaries that can potentially allow anticipatory decision-making policies of saving lives and maximizing the use of available capacity and resources.

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.

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster

It remains poorly understood how SARS-CoV-2 infection influences the physiological host factors important for aerosol transmission. We assessed breathing pattern, exhaled droplets, and infectious virus after infection with Alpha and Delta variants of concern (VOC) in the Syrian hamster. Both VOCs displayed a confined window of detectable airborne virus (24-48 hr), shorter than compared to oropharyngeal swabs. The loss of airborne shedding was linked to airway constriction resulting in a decrease of fine aerosols (1-10 µm) produced, which are suspected to be the major driver of airborne transmission. Male sex was associated with increased viral replication and virus shedding in the air. Next, we compared the transmission efficiency of both variants and found no significant differences. Transmission efficiency varied mostly among donors, 0-100% (including a superspreading event), and aerosol transmission over multiple chain links was representative of natural heterogeneity of exposure dose and downstream viral kinetics. Co-infection with VOCs only occurred when both viruses were shed by the same donor during an increased exposure timeframe (24-48 hr). This highlights that assessment of host and virus factors resulting in a differential exhaled particle profile is critical for understanding airborne transmission.

Aeromicrobiology: A global review of the cycling and relationships of bioaerosols with the atmosphere

Airborne microorganisms and biological matter (bioaerosols) play a key role in global biogeochemical cycling, human and crop health trends, and climate patterns. Their presence in the atmosphere is controlled by three main stages: emission, transport, and deposition. Aerial survival rates of bioaerosols are increased through adaptations such as ultra-violet radiation and desiccation resistance or association with particulate matter. Current research into modern concerns such as climate change, global gene transfer, and pathogenicity often neglects to consider atmospheric involvement. This comprehensive review outlines the transpiring of bioaerosols across taxa in the atmosphere, with significant focus on their interactions with environmental elements including abiotic factors (e.g., atmospheric composition, water cycle, and pollution) and events (e.g., dust storms, hurricanes, and wildfires). The aim of this review is to increase understanding and shed light on needed research regarding the interplay between global atmospheric phenomena and the aeromicrobiome. The abundantly documented bacteria and fungi are discussed in context of their cycling and human health impacts. Gaps in knowledge regarding airborne viral community, the challenges and importance of studying their composition, concentrations and survival in the air are addressed, along with understudied plant pathogenic oomycetes, and archaea cycling. Key methodologies in sampling, collection, and processing are described to provide an up-to-date picture of ameliorations in the field. We propose optimization to microbiological methods, commonly used in soil and water analysis, that adjust them to the context of aerobiology, along with other directions towards novel and necessary advancements. This review offers new perspectives into aeromicrobiology and calls for advancements in global-scale bioremediation, insights into ecology, climate change impacts, and pathogenicity transmittance.

Air Change Rate and SARS-CoV-2 Exposure in Hospitals and Residences: A Meta-Analysis

As SARS-CoV-2 swept across the globe, increased ventilation and implementation of air cleaning were emphasized by the US CDC and WHO as important strategies to reduce the risk of inhalation exposure to the virus. To assess whether higher ventilation and air cleaning rates lead to lower exposure risk to SARS-CoV-2, 1274 manuscripts published between April 2020 and September 2022 were screened using key words "airborne SARS-CoV-2 or "SARS-CoV-2 aerosol". Ninety-three studies involved air sampling at locations with known sources (hospitals and residences) were selected and associated data were compiled. Two metrics were used to assess exposure risk: SARS-CoV-2 concentration and SARS-CoV-2 detection rate in air samples. Locations were categorized by type (hospital or residence) and proximity to the sampling location housing the isolated/quarantined patient (primary or secondary). The results showed that hospital wards had lower airborne virus concentrations than residential isolation rooms. A negative correlation was found between airborne virus concentrations in primary-occupancy areas and air changes per hour (ACH). In hospital settings, sample positivity rates were significantly reduced in secondary-occupancy areas compared to primary-occupancy areas, but they were similar across sampling locations in residential settings. ACH and sample positivity rates were negatively correlated, though the effect was diminished when ACH values exceeded 8. While limitations associated with diverse sampling protocols exist, data considered by this meta-analysis support the notion that higher ACH may reduce exposure risks to the virus in ambient air.

Reduction of acute respiratory infections in day-care by non-pharmaceutical interventions: a narrative review

Objective

Children who start in day-care have 2-4 times as many respiratory infections compared to children who are cared for at home, and day-care staff are among the employees with the highest absenteeism. The extensive new knowledge that has been generated in the COVID-19 era should be used in the prevention measures we prioritize. The purpose of this narrative review is to answer the questions: Which respiratory viruses are the most significant in day-care centers and similar indoor environments? What do we know about the transmission route of these viruses? What evidence is there for the effectiveness of different non-pharmaceutical prevention measures?

Design

Literature searches with different terms related to respiratory infections in humans, mitigation strategies, viral transmission mechanisms, and with special focus on day-care, kindergarten or child nurseries, were conducted in PubMed database and Web of Science. Searches with each of the main viruses in combination with transmission, infectivity, and infectious spread were conducted separately supplemented through the references of articles that were retrieved.

Results

Five viruses were found to be responsible for ≈95% of respiratory infections: rhinovirus, (RV), influenza virus (IV), respiratory syncytial virus (RSV), coronavirus (CoV), and adenovirus (AdV). Novel research, emerged during the COVID-19 pandemic, suggests that most respiratory viruses are primarily transmitted in an airborne manner carried by aerosols (microdroplets).

Conclusion

Since airborne transmission is dominant for the most common respiratory viruses, the most important preventive measures consist of better indoor air quality that reduces viral concentrations and viability by appropriate ventilation strategies. Furthermore, control of the relative humidity and temperature, which ensures optimal respiratory functionality and, together with low resident density (or mask use) and increased time outdoors, can reduce the occurrence of respiratory infections.

On-site airborne pathogen detection for infection risk mitigation

Human-infecting pathogens that transmit through the air pose a significant threat to public health. As a prominent instance, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused the COVID-19 pandemic has affected the world in an unprecedented manner over the past few years. Despite the dissipating pandemic gloom, the lessons we have learned in dealing with pathogen-laden aerosols should be thoroughly reviewed because the airborne transmission risk may have been grossly underestimated. From a bioanalytical chemistry perspective, on-site airborne pathogen detection can be an effective non-pharmaceutic intervention (NPI) strategy, with on-site airborne pathogen detection and early-stage infection risk evaluation reducing the spread of disease and enabling life-saving decisions to be made. In light of this, we summarize the recent advances in highly efficient pathogen-laden aerosol sampling approaches, bioanalytical sensing technologies, and the prospects for airborne pathogen exposure measurement and evidence-based transmission interventions. We also discuss open challenges facing general bioaerosols detection, such as handling complex aerosol samples, improving sensitivity for airborne pathogen quantification, and establishing a risk assessment system with high spatiotemporal resolution for mitigating airborne transmission risks. This review provides a multidisciplinary outlook for future opportunities to improve the on-site airborne pathogen detection techniques, thereby enhancing the preparedness for more on-site bioaerosols measurement scenarios, such as monitoring high-risk pathogens on airplanes, weaponized pathogen aerosols, influenza variants at the workplace, and pollutant correlated with sick building syndromes.

The counterintuitive implications of superspreading diseases

The superspreading that characterized SARS and now COVID-19 can be rapidly quantified; however, its implications for outbreak control were never well understood. Recent studies point to its profound impact on outbreak dynamics and prospects for effective control of a future Disease X. These insights necessitate research into the mechanisms, impact and different modes of superspreading more widely.

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster

It remains poorly understood how SARS-CoV-2 infection influences the physiological host factors important for aerosol transmission. We assessed breathing pattern, exhaled droplets, and infectious virus after infection with Alpha and Delta variants of concern (VOC) in the Syrian hamster. Both VOCs displayed a confined window of detectable airborne virus (24-48 h), shorter than compared to oropharyngeal swabs. The loss of airborne shedding was linked to airway constriction resulting in a decrease of fine aerosols (1-10μm) produced, which are suspected to be the major driver of airborne transmission. Male sex was associated with increased viral replication and virus shedding in the air. Next, we compared the transmission efficiency of both variants and found no significant differences. Transmission efficiency varied mostly among donors, 0-100% (including a superspreading event), and aerosol transmission over multiple chain links was representative of natural heterogeneity of exposure dose and downstream viral kinetics. Co-infection with VOCs only occurred when both viruses were shed by the same donor during an increased exposure timeframe (24-48 h). This highlights that assessment of host and virus factors resulting in a differential exhaled particle profile is critical for understanding airborne transmission.

At the crossroads of epidemiology and biology: Bridging the gap between SARS-CoV-2 viral strain properties and epidemic wave characteristics

The COVID-19 pandemic has given rise to numerous articles from different scientific fields (epidemiology, virology, immunology, airflow physics …) without any effort to link these different insights. In this review, we aim to establish relationships between epidemiological data and the characteristics of the virus strain responsible for the epidemic wave concerned. We have carried out this study on the Wuhan, Alpha, Delta and Omicron strains allowing us to illustrate the evolution of the relationships we have highlighted according to these different viral strains. We addressed the following questions. 1) How can the mean infectious dose (one quantum, by definition in epidemiology) be measured and expressed as an amount of viral RNA molecules (in genome units, GU) or as a number of replicative viral particles (in plaque-forming units, PFU)? 2) How many infectious quanta are exhaled by an infected person per unit of time? 3) How many infectious quanta are exhaled, on average, integrated over the whole contagious period? 4) How do these quantities relate to the epidemic reproduction rate R as measured in epidemiology, and to the viral load, as measured by molecular biological methods? 5) How has the infectious dose evolved with the different strains of SARS-CoV-2? We make use of state-of-the-art modelling, reviewed and explained in the appendix of the article (Supplemental Information, SI), to answer these questions using data from the literature in both epidemiology and virology. We have considered the modification of these relationships according to the vaccination status of the population.

Characterization of superspreaders movement in a bidirectional corridor using a social force model

During infectious disease outbreaks, some infected individuals may spread the disease widely and amplify risks in the community. People whose daily activities bring them in close proximity to many others can unknowingly become superspreaders. The use of contact tracking based on social networks, GPS, or mobile tracking data can help to identify superspreaders and break the chain of transmission. We propose a model that aims at providing insight into risk factors of superspreading events. Here, we use a social force model to estimate the superspreading potential of individuals walking in a bidirectional corridor. First, we applied the model to identify parameters that favor exposure to an infectious person in scattered crowds. We find that low walking speed and high body mass both increase the expected number of close exposures. Panic events exacerbate the risks while social distancing reduces both the number and duration of close encounters. Further, in dense crowds, pedestrians interact more and cannot easily maintain the social distance between them. The number of exposures increases with the density of person in the corridor. The study of movements reveals that individuals walking toward the center of the corridor tend to rotate and zigzag more than those walking along the edges, and thus have higher risks of superspreading. The corridor model can be applied to designing risk reduction measures for specific high volume venues, including transit stations, stadiums, and schools.

Evaluation of droplet digital qRT-PCR (dd qRT-PCR) for quantification of SARS CoV-2 RNA in stool and urine specimens of COVID-19 patients

Introduction

There have been a few reports of viral load detection in stool and urine samples of patients with coronavirus disease 2019 (COVID-19), and the transmission of the virus through faecal oral route. For clinical diagnosis and treatment, the widely used reverse transcription-polymerase chain reaction (qRT-PCR) method has some limitations.

Methods

The aim of our study to assess the presence and concentration of SARS CoV-2 RNA in stool and urine samples from COVID-19 patients with mild, moderate, and severe disease, we compared a traditional qRT-PCR approach with a ddPCR. ddPCR and qRT-PCR-based target gene analysis were performed on 107 COVID-19-confirmed patients paired samples (N1 and N2). The MagMax magnetic beads base method was used to isolate RNA. Real-time qRT-PCR and dd PCR were performed on all patients.

Results and Discussion

The average cycle threshold (Ct) of qRT-PCR was highly correlated with the average copy number of 327.10 copies/l analyzed in ddPCR. In ddPCR, urine samples showed 27.1% positivity while for stool it was 100%.

Conclusion

This study's findings not only show that SARS CoV-2 is present in urine and faeces, but also suggest that low concentrations of the viral target ddPCR make it easier to identify positive samples and help resolve for cases of inconclusive diagnosis.

Real-time 4D tracking of airborne virus-laden droplets and aerosols

There is currently no real-time airborne virus tracking method, hindering the understanding of rapid virus changes and associated health impacts. Nano-digital in-line holographic microscopy (Nano-DIHM) is a lensless technology that can directly obtain the interference patterns of objects by recording the scattered light information originating from the objects. Here, we provide evidence for real-time physicochemical tracking of virus-laden droplets and aerosols in the air using desktop label-free Nano-DIHM. The virus interference patterns, as single and ensemble particles, were imaged by the Nano-DIHM with 32.5 ms resolution. The next-generation Stingray and Octopus software was used to automate object detection, characterization and classification from the recorded holograms. The detection system was demonstrated to detect active MS2 bacteriophages, inactivated SARS-CoV-2 and RNA fragments, and an MS2 mixture with metallic and organic compounds. This work demonstrates the feasibility of using Nano-DIHM to provide rapid virus detection to improve transmission management in real time.

Devendra Pal and coworkers report an imaging system using Nano-Digital in-line Holographic Microscopy (NanoDIHM) to detect airborne viruses in droplets and aerosols in real time. This system is able to detect various viruses in air, water and heterogeneous matrices within one minute, enabling real-time tracking of pollutant particles for efficient epidemic management.

Elevated soluble urokinase plasminogen activator receptor is associated with renal dysfunction in a Chlorocebus atheiops COVID-19 model

Increases of soluble urokinase plasminogen activator receptor (suPAR) were measured in both urine and plasma of a Chlorocebus aethiops (African green monkey; AGM) mucosal infected with SARS-CoV-2. The data indicate that elevated suPAR may be associated with renal dysfunction and pathology in the context of COVID-19.

Aerosol generation during coughing: an observational study

OBJECTIVE

Coronavirus disease 2019 has highlighted the lack of knowledge on aerosol exposure during respiratory activity and aerosol-generating procedures. This study sought to determine the aerosol concentrations generated by coughing to better understand, and to set a standard for studying, aerosols generated in medical procedures.

METHODS

Aerosol exposure during coughing was measured in 37 healthy volunteers in the operating theatre with an optical particle sizer, from 40 cm, 70 cm and 100 cm distances.

RESULTS

Altogether, 306 volitional and 15 involuntary coughs were measured. No differences between groups were observed.

CONCLUSION

Many medical procedures are expected to generate aerosols; it is unclear whether they are higher risk than normal respiratory activity. The measured aerosol exposure can be used to determine the risk for significant aerosol generation during medical procedures. Considerable variation of aerosol generation during cough was observed between individuals, but whether cough was volitional or involuntary made no difference to aerosol production.

Proteomic characteristics and diagnostic potential of exhaled breath particles in patients with COVID-19

BACKGROUND

SARS-CoV-2 has been shown to predominantly infect the airways and the respiratory tract and too often have an unpredictable and different pathologic pattern compared to other respiratory diseases. Current clinical diagnostical tools in pulmonary medicine expose patients to harmful radiation, are too unspecific or even invasive. Proteomic analysis of exhaled breath particles (EBPs) in contrast, are non-invasive, sample directly from the pathological source and presents as a novel explorative and diagnostical tool.

METHODS

Patients with PCR-verified COVID-19 infection (COV-POS, n = 20), and patients with respiratory symptoms but with > 2 negative polymerase chain reaction (PCR) tests (COV-NEG, n = 16) and healthy controls (HCO, n = 12) were prospectively recruited. EBPs were collected using a "particles in exhaled air" (PExA 2.0) device. Particle per exhaled volume (PEV) and size distribution profiles were compared. Proteins were analyzed using liquid chromatography-mass spectrometry. A random forest machine learning classification model was then trained and validated on EBP data achieving an accuracy of 0.92.

RESULTS

Significant increases in PEV and changes in size distribution profiles of EBPs was seen in COV-POS and COV-NEG compared to healthy controls. We achieved a deep proteome profiling of EBP across the three groups with proteins involved in immune activation, acute phase response, cell adhesion, blood coagulation, and known components of the respiratory tract lining fluid, among others. We demonstrated promising results for the use of an integrated EBP biomarker panel together with particle concentration for diagnosis of COVID-19 as well as a robust method for protein identification in EBPs.

CONCLUSION

Our results demonstrate the promising potential for the use of EBP fingerprints in biomarker discovery and for diagnosing pulmonary diseases, rapidly and non-invasively with minimal patient discomfort.

The impact of mean body mass index on reported mortality from COVID-19 across 181 countries

Accountability for global health issues such as a pandemic and its devastating consequences are usually ascribed to a virus, but a comprehensive view should also take into account the state of the host. Data suggests that excessive nutrition is to blame for a yet unknown but not negligible portion of deaths attributed to severe acute respiratory syndrome coronavirus 2. We analyzed the correlation between mean body mass index (BMI) and 2-year coronavirus disease 2019 (COVID-19) mortality rates reported by 181 countries worldwide. Almost two thirds of the countries included had a mean BMI greater or equal to 25, with death rates ranging from 3 to 6,280 per million. Death rates in countries with a mean BMI below 25 ranged from 3 to 1,533. When the analysis was restricted to countries where the extent of testing was deemed more representative of actual mortality, only 20.1% had a mean BMI <25 but the mortality difference persisted. A second analysis looking at pre-vaccination mortality obtained from a different source led to similar conclusions. Due to the nature of the variables, reverse causation can be excluded while common causation can not. A mean BMI <25 for a country seems to spare its citizens from the highest COVID-19 mortality rates. The impact of excess weight on global COVID-19 mortality is suspected to have been much higher than what currently perceived, here estimated at no less than a fourfold increase in mortality. Countries with normal mean BMI constitute precious test beds for the quantification of the effects of overeating on COVID-19 mortality.

Indoor air surveillance and factors associated with respiratory pathogen detection in community settings in Belgium

Currently, the real-life impact of indoor climate, human behaviour, ventilation and air filtration on respiratory pathogen detection and concentration are poorly understood. This hinders the interpretability of bioaerosol quantification in indoor air to surveil respiratory pathogens and transmission risk. We tested 341 indoor air samples from 21 community settings in Belgium for 29 respiratory pathogens using qPCR. On average, 3.9 pathogens were positive per sample and 85.3% of samples tested positive for at least one. Pathogen detection and concentration varied significantly by pathogen, month, and age group in generalised linear (mixed) models and generalised estimating equations. High CO2 and low natural ventilation were independent risk factors for detection. The odds ratio for detection was 1.09 (95% CI 1.03-1.15) per 100 parts per million (ppm) increase in CO2, and 0.88 (95% CI 0.80-0.97) per stepwise increase in natural ventilation (on a Likert scale). CO2 concentration and portable air filtration were independently associated with pathogen concentration. Each 100ppm increase in CO2 was associated with a qPCR Ct value decrease of 0.08 (95% CI -0.12 to -0.04), and portable air filtration with a 0.58 (95% CI 0.25-0.91) increase. The effects of occupancy, sampling duration, mask wearing, vocalisation, temperature, humidity and mechanical ventilation were not significant. Our results support the importance of ventilation and air filtration to reduce transmission.

Respiratory aerosol particle emission and simulated infection risk is greater during indoor endurance than resistance exercise

Pathogens such as severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), influenza, and rhinoviruses are transmitted by airborne aerosol respiratory particles that are exhaled by infectious subjects. We have previously reported that the emission of aerosol particles increases on average 132-fold from rest to maximal endurance exercise. The aims of this study are to first measure aerosol particle emission during an isokinetic resistance exercise at 80% of the maximal voluntary contraction until exhaustion, second to compare aerosol particle emission during a typical spinning class session versus a three-set resistance training session. Finally, we then used this data to calculate the risk of infection during endurance and resistance exercise sessions with different mitigation strategies. During a set of isokinetic resistance exercise, aerosol particle emission increased 10-fold from 5,400 ± 1,200 particles/min at rest to 59,000 ± 69,900 particles/min during a set of resistance exercise. We found that aerosol particle emission per minute is on average 4.9-times lower during a resistance training session than during a spinning class. Using this data, we determined that the simulated infection risk increase during an endurance exercise session was sixfold higher than during a resistance exercise session when assuming one infected participant in the class. Collectively, this data helps to select mitigation measures for indoor resistance and endurance exercise classes at times where the risk of aerosol-transmitted infectious disease with severe outcomes is high.

Inhalation of virus-loaded droplets as a clinically plausible pathway to deep lung infection

Respiratory viruses, such as SARS-CoV-2, preliminarily infect the nasopharyngeal mucosa. The mechanism of infection spread from the nasopharynx to the deep lung-which may cause a severe infection-is, however, still unclear. We propose a clinically plausible mechanism of infection spread to the deep lung through droplets, present in the nasopharynx, inhaled and transported into the lower respiratory tract. A coupled mathematical model of droplet, virus transport and virus infection kinetics is exercised to demonstrate clinically observed times to deep lung infection. The model predicts, in agreement with clinical observations, that severe infection can develop in the deep lung within 2.5-7 days of initial symptom onset. Results indicate that while fluid dynamics plays an important role in transporting the droplets, infection kinetics and immune responses determine infection growth and resolution. Immune responses, particularly antibodies and T-lymphocytes, are observed to be critically important for preventing infection severity. This reinforces the role of vaccination in preventing severe infection. Managing aerosolization of infected nasopharyngeal mucosa is additionally suggested as a strategy for minimizing infection spread and severity.

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.

Exhaled aerosols among PCR-confirmed SARS-CoV-2-infected children

Background

Available data on aerosol emissions among children and adolescents during spontaneous breathing are limited. Our aim was to gain insight into the role of children in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and whether aerosol measurements among children can be used to help detect so-called superspreaders-infected individuals with extremely high numbers of exhaled aerosol particles.

Methods

In this prospective study, the aerosol concentrations of SARS-CoV-2 PCR-positive and SARS-CoV-2 PCR-negative children and adolescents (2-17 years) were investigated. All subjects were asked about their current health status and medical history. The exhaled aerosol particle counts of PCR-negative and PCR-positive subjects were measured using the Resp-Aer-Meter (Palas GmbH, Karlsruhe, Germany) and compared using linear regression.

Results

A total of 250 children and adolescents were included in this study, 105 of whom were SARS-CoV-2 positive and 145 of whom were SARS-CoV-2 negative. The median age in both groups was 9 years (IQR 7-11 years). A total of 124 (49.6%) participants were female, and 126 (50.4%) participants were male. A total of 81.9% of the SARS-CoV-2-positive group had symptoms of viral infection. The median particle count of all individuals was 79.55 particles/liter (IQR 44.55-141.15). There was a tendency for older children to exhale more particles (1-5 years: 79.54 p/L; 6-11 years: 77.96 p/L; 12-17 years: 98.63 p/L). SARS-CoV-2 PCR status was not a bivariate predictor (t = 0.82, p = 0.415) of exhaled aerosol particle count; however, SARS-CoV-2 status was shown to be a significant predictor in a multiple regression model together with age, body mass index (BMI), COVID-19 vaccination, and past SARS-CoV-2 infection (t = 2.81, p = 0.005). COVID-19 vaccination status was a highly significant predictor of exhaled aerosol particles (p < .001).

Conclusion

During SARS-CoV-2 infection, children and adolescents did not have elevated aerosol levels. In addition, no superspreaders were found.

Can nonvolatile tastants be smelled during food oral processing?

While accumulating evidence implied the involvement of retro-nasal sensation in the consumption of nonvolatile taste compounds, it is still unclear whether it was caused by the taste compounds themselves, and if so, how can they migrate from the oral to nasal cavity. At first, we proposed aerosol particles as an alternative oral-nasal mass transfer mechanism. The high-speed camera approved that aerosol particles could be generated by the typical oral and pharynx actions during food oral processing; while the narrow-band imaging of nasal cleft and mass spectrometry of nostril-exhaled air approved the migration of aerosol within the oral-nasal route. Then, the "smelling" of taste compounds within the aerosol particles was testified. The four-alternative forced choices (4AFC) approved that the potential volatile residues or contaminants within the headspace air of pure taste solution cannot arouse significant smell, while the taste compounds embedded in the in vitro prepared aerosol particles can be "smelled" via the ortho route. The "smell" of sucrose is very different from its taste and the "smell" of quinine, implying its actual olfaction. The sweetness intensity of sucrose solution was also reduced when the volunteers' noses were clipped, indicating the involvement of retro-nasal sensation during its drinking. At last, the efficiency of aerosol as a mechanism of oral-nasal mass transfer was demonstrated to be comparable with the volatile molecules under the experimental condition, giving it the potential to be a substantial and unique source of retro-nasal sensation during food oral processing.

On-Site Quantification and Infection Risk Assessment of Airborne SARS-CoV-2 Virus Via a Nanoplasmonic Bioaerosol Sensing System in Healthcare Settings

On-site quantification and early-stage infection risk assessment of airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with high spatiotemporal resolution is a promising approach for mitigating the spread of coronavirus disease 2019 (COVID-19) pandemic and informing life-saving decisions. Here, a condensation (hygroscopic growth)-assisted bioaerosol collection and plasmonic photothermal sensing (CAPS) system for on-site quantitative risk analysis of SARS-CoV-2 virus-laden aerosols is presented. The CAPS system provided rapid thermoplasmonic biosensing results after an aerosol-to-hydrosol sampling process in COVID-19-related environments including a hospital and a nursing home. The detection limit reached 0.25 copies/µL in the complex aerosol background without further purification. More importantly, the CAPS system enabled direct measurement of the SARS-CoV-2 virus exposures with high spatiotemporal resolution. Measurement and feedback of the results to healthcare workers and patients via a QR-code are completed within two hours. Based on a dose-responseµ model, it is used the plasmonic biosensing signal to calculate probabilities of SARS-CoV-2 infection risk and estimate maximum exposure durations to an acceptable risk threshold in different environmental settings.

Comparison of Dose-Response Relationships for Two Isolates of SARS-CoV-2 in a Nonhuman Primate Model of Inhalational COVID-19

Background: As the COVID-19 pandemic has progressed, numerous variants of SARS-CoV-2 have arisen, with several displaying increased transmissibility. Methods: The present study compared dose-response relationships and disease presentation in nonhuman primates infected with aerosols containing an isolate of the Gamma variant of SARS-CoV-2 to the results of our previous study with the earlier WA-1 isolate of SARS-CoV-2. Results: Disease in Gamma-infected animals was mild, characterized by dose-dependent fever and oronasal shedding of virus. Differences were observed in shedding in the upper respiratory tract between Gamma- and WA-1-infected animals that have the potential to influence disease transmission. Specifically, the estimated median doses for shedding of viral RNA or infectious virus in nasal swabs were approximately 10-fold lower for the Gamma variant than the WA-1 isolate. Given that the median doses for fever were similar, this suggests that there is a greater difference between the median doses for viral shedding and fever for Gamma than for WA-1 and potentially an increased range of doses for Gamma over which asymptomatic shedding and disease transmission are possible. Conclusions: These results complement those of previous studies, which suggested that differences in exposure dose may help to explain the range of clinical disease presentations observed in individuals with COVID-19, highlighting the importance of public health measures designed to limit exposure dose, such as masking and social distancing. The dose-response data provided by this study are important to inform disease transmission and hazard modeling, as well as to inform dose selection in future studies examining the efficacy of therapeutics and vaccines in animal models of inhalational COVID-19.

Intrinsic host susceptibility among multiple species to intranasal SARS-CoV-2 identifies diverse virological, biodistribution and pathological outcomes

SARS-CoV-2 exhibits a diverse host species range with variable outcomes, enabling differential host susceptibility studies to assess suitability for pre-clinical countermeasure and pathogenesis studies. Baseline virological, molecular and pathological outcomes were determined among multiple species-one Old World non-human primate (NHP) species (cynomolgus macaques), two New World NHP species (red-bellied tamarins; common marmosets) and Syrian hamsters-following single-dose, atraumatic intranasal administration of SARS-CoV-2/Victoria-01. After serial sacrifice 2, 10 and 28-days post-infection (dpi), hamsters and cynomolgus macaques displayed differential virus biodistribution across respiratory, gastrointestinal and cardiovascular systems. Uniquely, New World tamarins, unlike marmosets, exhibited high levels of acute upper airway infection, infectious virus recovery associated with mild lung pathology representing a host previously unrecognized as susceptible to SARS-CoV-2. Across all species, lung pathology was identified post-clearance of virus shedding (antigen/RNA), with an association of virus particles within replication organelles in lung sections analysed by electron microscopy. Disrupted cell ultrastructure and lung architecture, including abnormal morphology of mitochondria 10-28 dpi, represented on-going pathophysiological consequences of SARS-CoV-2 in predominantly asymptomatic hosts. Infection kinetics and host pathology comparators using standardized methodologies enables model selection to bridge differential outcomes within upper and lower respiratory tracts and elucidate longer-term consequences of asymptomatic SARS-CoV-2 infection.

Experience of the COVID-19 pandemic in Wuhan leads to a lasting increase in social distancing

On 11th Jan 2020, the first COVID-19 related death was confirmed in Wuhan, Hubei. The Chinese government responded to the outbreak with a lockdown that impacted most residents of Hubei province and lasted for almost three months. At the time, the lockdown was the strictest both within China and worldwide. Using an interactive web-based experiment conducted half a year after the lockdown with participants from 11 Chinese provinces, we investigate the behavioral effects of this 'shock' event experienced by the population of Hubei. We find that both one's place of residence and the strictness of lockdown measures in their province are robust predictors of individual social distancing behavior. Further, we observe that informational messages are effective at increasing compliance with social distancing throughout China, whereas fines for noncompliance work better within Hubei province relative to the rest of the country. We also report that residents of Hubei increase their propensity to social distance when exposed to social environments characterized by the presence of a superspreader, while the effect is not present outside of the province. Our results appear to be specific to the context of COVID-19 and are not explained by general differences in risk attitudes and social preferences.

The airborne contagiousness of respiratory viruses: A comparative analysis and implications for mitigation

The infectious emission rate is a fundamental input parameter for airborne transmission risk assessment, but data are limited due to reliance on estimates from chance superspreading events. This study assesses the strength of a predictive estimation approach developed by the authors for SARS-CoV-2 and uses novel estimates to compare the contagiousness of respiratory pathogens. We applied the approach to SARS-CoV-1, SARS-CoV-2, MERS, measles virus, adenovirus, rhinovirus, coxsackievirus, seasonal influenza virus and Mycobacterium tuberculosis (TB) and compared quanta emission rate (ERq) estimates to literature values. We calculated infection risk in a prototypical classroom and barracks to assess the relative ability of ventilation to mitigate airborne transmission. Our median standing and speaking ERq estimate for SARS-CoV-2 (2.7 quanta h-1) is similar to active, untreated TB (3.1 quanta h-1), higher than seasonal influenza (0.17 quanta h-1), and lower than measles virus (15 quanta h-1). We calculated event reproduction numbers above 1 for SARS-CoV-2, measles virus, and untreated TB in both the classroom and barracks for an activity level of standing and speaking at low, medium and high ventilation rates of 2.3, 6.6 and 14 L per second per person (L s-1 p-1), respectively. Our predictive ERq estimates are consistent with the range of values reported over decades of research. In congregate settings, current ventilation standards are unlikely to control the spread of viruses with upper quartile ERq values above 10 quanta h-1, such as SARS-CoV-2, indicating the need for additional control measures.

Mathematical modeling to study the impact of immigration on the dynamics of the COVID-19 pandemic: A case study for Venezuela

We propose two different mathematical models to study the effect of immigration on the COVID-19 pandemic. The first model does not consider immigration, whereas the second one does. Both mathematical models consider five different subpopulations: susceptible, exposed, infected, asymptomatic carriers, and recovered. We find the basic reproduction number R₀ using the next-generation matrix method for the mathematical model without immigration. This threshold parameter is paramount because it allows us to characterize the evolution of the disease and identify what parameters substantially affect the COVID-19 pandemic outcome. We focus on the Venezuelan scenario, where immigration and emigration have been important over recent years, particularly during the pandemic. We show that the estimation of the transmission rates of the SARS-CoV-2 are affected when the immigration of infected people is considered. This has an important consequence from a public health perspective because if the basic reproduction number is less than unity, we can expect that the SARS-CoV-2 would disappear. Thus, if the basic reproduction number is slightly above one, we can predict that some mild non-pharmaceutical interventions would be enough to decrease the number of infected people. The results show that the dynamics of the spread of SARS-CoV-2 through the population must consider immigration to obtain better insight into the outcomes and create awareness in the population regarding the population flow.

Snoring may transmit infectious aerosols from the upper to the lower respiratory tract

Migration to the lungs of an initial upper airway infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or other respiratory pathogens can lead to pneumonia, associated with progression from mild to severe symptoms. Chemical pneumonitis or bacterial pneumonia may be caused by the ‘macroaspiration’ of large volumes of oropharyngeal or gastroesophageal secretions into the lower respiratory tract. ‘Microaspiration’, i.e., a similar mechanism but involving much smaller amounts of oropharyngeal secretions, is considered the pathogenetic mechanism for most pneumonias, including that associated with COVID-19. Here, we hypothesize an alternative mechanism: Rather than by microaspiration, these fluids enter the lungs as microdroplets that are generated by snoring and then carried by the inspired airstream. Laboratory measurements indicate that snoring generates (a) comparable numbers and sizes of oral fluid droplets as loud speaking and (b) total fluid quantities that are similar to those reported for microaspiration. Snoring propensity is strongly correlated to known risk factors for severe COVID-19, including male gender, age, obesity, diabetes, obstructive sleep apnea, and pregnancy. Therefore, more research is urgently needed to determine if various methods that decrease snoring can prevent progression to pneumonia after initial infection of the upper airways.

Genetic Load of SARS-CoV-2 in Aerosols Collected in Operating Theaters

After the outbreak of COVID-19, additional protocols have been established to prevent the transmission of the SARS-CoV-2 from the patient to the health personnel and vice versa in health care settings. However, in the case of emergency surgeries, it is not always possible to ensure that the patient is not infected with SARS-CoV-2, assuming a potential source of transmission of the virus to health personnel. This work aimed to evaluate the presence of the SARS-CoV-2 and quantify the viral load in indoor air samples collected inside operating rooms, where emergency and scheduled operations take place. Samples were collected for 3 weeks inside two operating rooms for 24 h at 38 L/min in quartz filters. RNA was extracted from the filters and analyzed using RT-qPCR targeting SARS-CoV-2 genes E, N1 and N2 regions. SARS-CoV-2 RNA was detected in 11.3% of aerosol samples collected in operating rooms, despite with low concentrations (not detected at 13.5 cg/m³ and 10.5 cg/m³ in the scheduled and emergency operating rooms, respectively). Potential sources of airborne SARS-CoV-2 could be aerosolization of the virus during aerosol-generating procedures and in open surgery from patients that might have been recently infected with the virus, despite presenting a negative COVID-19 test. Another source could be related to health care workers unknowingly infected with the virus and exhaling SARS-CoV-2 virions into the air. These results highlight the importance of reinforcing preventive measures against COVID-19 in operating rooms, such as the correct use of protective equipment, screening programs for health care workers, and information campaigns. IMPORTANCE Operating rooms are critical environments in which asepsis must be ensured. The COVID-19 pandemic entailed the implementation of additional preventative measures in health care settings, including operating theaters. Although one of the measures is to operate only COVID-19 free patients, this measure cannot be always implemented, especially in emergency interventions. Therefore, a surveillance campaign was conducted during 3 weeks in two operating rooms to assess the level of SARS-CoV-2 genetic material detected in operating theaters with the aim to assess the risk of COVID-19 transmission during operating procedures. SARS-CoV-2 genetic material was detected in 11% of aerosol samples collected in operating rooms, despite with low concentrations. Plausible SARS-CoV-2 sources have been discussed, including patients and health care personnel infected with the virus. These results highlight the importance of reinforcing preventive measures against COVID-19 in operating rooms, such as the correct use of protective equipment, screening programs for health care workers and information campaigns.

Assessing the consequences of prolonged usage of disposable face masks

Due to the SARS-CoV-2 outbreak, wearing a disposable face mask has become a worldwide daily routine, not only for medical operators or specialized personnel, but also for common people. Notwithstanding the undeniable positive effect in reducing the risk of virus transmission, it is important to understand if a prolonged usage of the same face mask can have effectiveness on filtering capability and potential health consequences. To this aim, we present three investigations. A survey, carried out in central Italy, offers an overview of the distorted public awareness of face mask usage. A functional study shows how prolonged wearing leads to substantial drops in humid air filtration efficiency. Finally, a morphological analysis reports the proliferation of fungal or bacteria colonies inside an improperly used mask. Our study highlights therefore that wearing a face mask is really beneficial only if it is used correctly.

Sequence difference of angiotensin-converting enzyme 2 between nonhuman primates affects its binding-affinity with SARS-CoV-2 S receptor binding domain

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused many deaths and contributed to a tremendous public health concern worldwide since 2020. Angiotensin-converting enzyme 2 (ACE2) binds to the SARS-CoV-2 virus as a receptor. The challenge of different nonhuman primate (NHP) species by SARS-CoV-2 virus demonstrated different effects on virus replication and disease pathology. This study characterizes differences between host ACE2 sequences of three NHP species: Macaca mulatta, Macaca fascicularis, and Chlorocebus sabaeus. In addition, the binding affinity between the ACE2 ectodomain and the SARS-CoV-2 S receptor-binding domain (RBD) was analyzed. Variation of ACE2 sequence among NHP species and the binding affinity may account for different susceptibility and responses to SARS-CoV-2 infection.

SARS-CoV-2 indoor environment contamination with epidemiological and experimental investigations

SARS-CoV-2 has been detected both in air and on surfaces, but questions remain about the patient-specific and environmental factors affecting virus transmission. Additionally, more detailed information on viral sampling of the air is needed. This prospective cohort study (N = 56) presents results from 258 air and 252 surface samples from the surroundings of 23 hospitalized and eight home-treated COVID-19 index patients between July 2020 and March 2021 and compares the results between the measured environments and patient factors. Additionally, epidemiological and experimental investigations were performed. The proportions of qRT-PCR-positive air (10.7% hospital/17.6% homes) and surface samples (8.8%/12.9%) showed statistical similarity in hospital and homes. Significant SARS-CoV-2 air contamination was observed in a large (655.25 m³ ) mechanically ventilated (1.67 air changes per hour, 32.4-421 L/s/patient) patient hall even with only two patients present. All positive air samples were obtained in the absence of aerosol-generating procedures. In four cases, positive environmental samples were detected after the patients had developed a neutralizing IgG response. SARS-CoV-2 RNA was detected in the following particle sizes: 0.65-4.7 μm, 7.0-12.0 μm, >10 μm, and <100 μm. Appropriate infection control against airborne and surface transmission routes is needed in both environments, even after antibody production has begun.

Incidence, Hospitalization, Mortality and Risk Factors of COVID-19 in Long-Term Care Residential Homes for Patients with Chronic Mental Illness

Long-term care residential homes (LTCRH) for patients with chronic mental illness have suffered the enormous impact of COVID-19. This study aimed to estimate incidence, hospitalization, mortality, and risk factors of COVID-19 to prevent future epidemics. From March 2020 to January 2021 and before vaccination anti-SARS-CoV-2 begins, cumulate incidence rate (CIR), hospitalization rate (HR), mortality rate (MR), and risk factors of COVID-19 in the 11 LTCRH of two Health Departments of Castellon (Spain) were studied by epidemiological surveillance and an ecological design. Laboratory tests confirmed COVID-19 cases, and multilevel Poisson regression models were employed. All LTCRH participated and comprised 346 residents and 482 staff. Residents had a mean age of 47 years, 40% women, and suffered 75 cases of COVID-19 (CIR = 21.7%), five hospitalizations (HR = 1.4%), and two deaths (MR = 0.6%) with 2.5% fatality-case. Staff suffered 74 cases of the disease (CIR = 15.4%), one hospitalization (HR = 0.2%), and no deaths were reported. Risk factors associated with COVID-19 incidence in residents were private ownership, severe disability, residents be younger, CIR in municipalities where LTCRH was located, CIR in staff, and older age of the facilities. Conclusion: COVID-19 incidence could be prevented by improving infection control in residents and staff and modernizing facilities with increased public ownership.

The physics of respiratory particle generation, fate in the air, and inhalation

Given that breathing is one of the most fundamental physiological functions, there is an urgent need to broaden our understanding of the fluid dynamics that governs it. There would be many benefits from doing so, including a better assessment of respiratory health, a basis for more precise delivery of pharmaceutical drugs for treatment, and the understanding and potential minimization of respiratory infection transmission. We review the physics of particle generation in the respiratory tract, the fate of these particles in the air on exhalation and the physics of particle inhalation. The main focus is on evidence from experimental studies. We conclude that although there is qualitative understanding of the generation of particles in the respiratory tract, a basic quantitative knowledge of the characteristics of the particles emitted during respiratory activities and their fate after emission, and a theoretical understanding of particle deposition during inhalation, nevertheless the general understanding of the entire process is rudimentary, and many open questions remain.

Different forms of superspreading lead to different outcomes: Heterogeneity in infectiousness and contact behavior relevant for the case of SARS-CoV-2

Superspreading events play an important role in the spread of several pathogens, such as SARS-CoV-2. While the basic reproduction number of the original Wuhan SARS-CoV-2 is estimated to be about 3 for Belgium, there is substantial inter-individual variation in the number of secondary cases each infected individual causes—with most infectious individuals generating no or only a few secondary cases, while about 20% of infectious individuals is responsible for 80% of new infections. Multiple factors contribute to the occurrence of superspreading events: heterogeneity in infectiousness, individual variations in susceptibility, differences in contact behavior, and the environment in which transmission takes place. While superspreading has been included in several infectious disease transmission models, research into the effects of different forms of superspreading on the spread of pathogens remains limited. To disentangle the effects of infectiousness-related heterogeneity on the one hand and contact-related heterogeneity on the other, we implemented both forms of superspreading in an individual-based model describing the transmission and spread of SARS-CoV-2 in a synthetic Belgian population. We considered its impact on viral spread as well as on epidemic resurgence after a period of social distancing. We found that the effects of superspreading driven by heterogeneity in infectiousness are different from the effects of superspreading driven by heterogeneity in contact behavior. On the one hand, a higher level of infectiousness-related heterogeneity results in a lower risk of an outbreak persisting following the introduction of one infected individual into the population. Outbreaks that did persist led to fewer total cases and were slower, with a lower peak which occurred at a later point in time, and a lower herd immunity threshold. Finally, the risk of resurgence of an outbreak following a period of lockdown decreased. On the other hand, when contact-related heterogeneity was high, this also led to fewer cases in total during persistent outbreaks, but caused outbreaks to be more explosive in regard to other aspects (such as higher peaks which occurred earlier, and a higher herd immunity threshold). Finally, the risk of resurgence of an outbreak following a period of lockdown increased. We found that these effects were conserved when testing combinations of infectiousness-related and contact-related heterogeneity.

To investigate the effect of different sources of superspreading on disease dynamics, we implemented superspreading driven by heterogeneity in infectiousness and heterogeneity in contact behavior into an individual-based model for the transmission of SARS-CoV-2 in the Belgian population. We compared the impact of both forms of superspreading in a scenario without interventions as well as in a scenario in which a period of strict social distancing (i.e. a lockdown) is followed by a period of partial release. We found that both forms of superspreading have very different effects. On the one hand, increasing the level of infectiousness-related heterogeneity led to less outbreaks being observed following the introduction of one infected individual in the population. Furthermore, final outbreak sizes decreased, and outbreaks became slower, with lower and later peaks, and a lower herd immunity threshold. Finally, the risk for resurgence of an outbreak following a period of lockdown also decreased. On the other hand, when contact-related heterogeneity was high, this also led to smaller final sizes, but caused outbreaks to be more explosive regarding other aspects (such as higher peaks that occurred earlier). The herd immunity threshold also increased, as did the risk of resurgence of outbreaks.

What were the historical reasons for the resistance to recognizing airborne transmission during the COVID-19 pandemic?

The question of whether SARS-CoV-2 is mainly transmitted by droplets or aerosols has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human history, the dominant paradigm was that many diseases were carried by the air, often over long distances and in a phantasmagorical way. This miasmatic paradigm was challenged in the mid to late 19th century with the rise of germ theory, and as diseases such as cholera, puerperal fever, and malaria were found to actually transmit in other ways. Motivated by his views on the importance of contact/droplet infection, and the resistance he encountered from the remaining influence of miasma theory, prominent public health official Charles Chapin in 1910 helped initiate a successful paradigm shift, deeming airborne transmission most unlikely. This new paradigm became dominant. However, the lack of understanding of aerosols led to systematic errors in the interpretation of research evidence on transmission pathways. For the next five decades, airborne transmission was considered of negligible or minor importance for all major respiratory diseases, until a demonstration of airborne transmission of tuberculosis (which had been mistakenly thought to be transmitted by droplets) in 1962. The contact/droplet paradigm remained dominant, and only a few diseases were widely accepted as airborne before COVID-19: those that were clearly transmitted to people not in the same room. The acceleration of interdisciplinary research inspired by the COVID-19 pandemic has shown that airborne transmission is a major mode of transmission for this disease, and is likely to be significant for many respiratory infectious diseases.

SARS-CoV-2 air sampling: A systematic review on the methodologies for detection and infectivity

This systematic review aims to present an overview of the current aerosol sampling methods (and equipment) being used to investigate the presence of SARS-CoV-2 in the air, along with the main parameters reported in the studies that are essential to analyze the advantages and disadvantages of each method and perspectives for future research regarding this mode of transmission. A systematic literature review was performed on PubMed/MEDLINE, Web of Science, and Scopus to assess the current air sampling methodologies being applied to SARS-CoV-2. Most of the studies took place in indoor environments and healthcare settings and included air and environmental sampling. The collection mechanisms used were impinger, cyclone, impactor, filters, water-based condensation, and passive sampling. Most of the reviewed studies used RT-PCR to test the presence of SARS-CoV-2 RNA in the collected samples. SARS-CoV-2 RNA was detected with all collection mechanisms. From the studies detecting the presence of SARS-CoV-2 RNA, fourteen assessed infectivity. Five studies detected viable viruses using impactor, water-based condensation, and cyclone collection mechanisms. There is a need for a standardized protocol for sampling SARS-CoV-2 in air, which should also account for other influencing parameters, including air exchange ratio in the room sampled, relative humidity, temperature, and lighting conditions.

Ultralight and Ultrathin Electrospun Membranes with Enhanced Air Permeability for Chemical and Biological Protection

With the growing interest in chemical and biological warfare agents (CWAs/BWAs), the focus has shifted toward aerosol protection using protective clothing. However, compared to air-permeable membranes, those with water vapor permeability have been investigated more extensively. Filtering membranes without air permeability have limited practical usage in personal protective suits and masks. In this study, polyacrylonitrile membranes with tightly attached activated carbon and doped copper(II) oxide were prepared via electrospinning. The nanofibers with uniformly controlled diameters and smooth morphologies enable water/air breathability and protection against aerosol (100 nm polystyrene nanobeads similar to SARS-CoV-2) penetration. The uniformly distributed and tightly attached activated carbon and doped copper(II) oxide particles enhance the sorptive performance of the membranes by blocking gaseous CWAs, including soman, nerve chemical agents, and BWAs. Such dual-purpose membranes can be implemented in protective equipment owing to their high performance and easy processing.

Hybrid measurement of respiratory aerosol reveals a dominant coarse fraction resulting from speech that remains airborne for minutes

Respiratory droplets are widely recognized as the primary vehicle in viral respiratory disease transmission. Accurate information on their number and size distributions is important for appropriate mitigation strategies, for quantitative modeling of airborne disease transmission, and for evaluating the relative importance of droplets originating from saliva versus airway lining fluid. A straightforward experimental setup using inexpensive, readily available components is developed for simultaneous characterization of larger particles by video analysis of laser light scattering and monitoring of smaller sizes by an optical particle counter. Measurements indicate that in a healthy volunteer, the airborne mass of speech aerosol far exceeds that generated by breathing, even when accounting for faster sedimentation of the larger particles.

Accurate measurements of the size and quantity of aerosols generated by various human activities in different environments are required for efficacious mitigation strategies and accurate modeling of respiratory disease transmission. Previous studies of speech droplets, using standard aerosol instrumentation, reported very few particles larger than 5 μm. This starkly contrasts with the abundance of such particles seen in both historical slide deposition measurements and more recent light scattering observations. We have reconciled this discrepancy by developing an alternative experimental approach that addresses complications arising from nucleated condensation. Measurements reveal that a large volume fraction of speech-generated aerosol has diameters in the 5- to 20-μm range, making them sufficiently small to remain airborne for minutes, not hours. This coarse aerosol is too large to penetrate the lower respiratory tract directly, and its relevance to disease transmission is consistent with the vast majority of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections initiating in the upper respiratory tract. Our measurements suggest that in the absence of symptoms such as coughing or sneezing, the importance of speech-generated aerosol in the transmission of respiratory diseases is far greater than generally recognized.

Bioaerosols and airborne transmission: Integrating biological complexity into our perspective

There is broad consensus that airborne disease transmission continues to be the thematic focus of COVID-19, the complexities and understanding of which continues to complicate our attempts to control this pandemic. Masking used as both personal protection and source reduction predominates our society at present and, other than vaccination, remains the public health measure that will faithfully reduce aerosol transmission and overall disease burden (Gandhi and Marr, 2021). Early in the advent of the COVID-19 pandemic, and especially after preliminary recognition of airborne transmission, there was considerable efforts in the application of computational fluid dynamics (CFD) modeling aerosols as well as risk models calculations, the products of which were detailed in the literature (Morawska et al., 2020; Buonanno et al., 2020a) and even disseminated in media destined for the public. As the respiratory pathway emerged as the dominant exposure pathway for SARSCoV-2 transmission, much of what was promoted from CFD was applied to risk models to estimate community infection and in some cases expected clinical outcome. COVID-19 proved to fit the profile of an obligate respiratory-transmitted pathogen, and the plausibility of using aerosol modeling when silhouetted with emerging COVID-19 epidemiology provided ample evidence for promotion of masking and ventilation optimization as a required public health measure. Masking is often included as a factor in developed risk models and it remains an essentially important part of our response to this airborne threat, and ultimately will agnostically reduce disease burden although efforts to improve ventilation in indoor spaces remain a challenge. Arguably the most important concept in the airborne transmission of infectious agents is the biologically active componentry that comprises the aerosol particle and the functional dynamic nature of particle contents. Specifically, the innate generation, transport, and ultimate deposition/disposition of bioaerosols; the aerosol particles that nearly exclusively harbor bioactive components, including viruses, when disease agents are transmitted through the air.

Healthcare workers, epidemic biological risks - recommendations based on the experience with COVID-19 and Ebolavirus

Infectious disease outbreaks frequently cause illness and death among Healthcare Workers (HCWs). We compare strategies from recent, past and ongoing outbreak measures used to protect HCWs, including those facing additional challenges such as racial disparities, violence and stigmatization. Outbreaks and pandemics superimposed on countries with preexisting crises have also affected emergency response to these viral outbreaks. Strategies to protect HCWs include adherence to recommended infection prevention and control measures; new technology such as rapid point-of-care tests and remote monitoring; adopting national public health preparedness plans to ensure the supply and allocation of PPE, staff, and testing supplies; occupational health and mental health support services. Lessons learned from recent pandemics should be used by Infection Prevention and Control and Occupational Health staff to refine preparedness plans to protect HCWs better.

Aerosol particle emission increases exponentially above moderate exercise intensity resulting in superemission during maximal exercise

Airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or other pathogens is probably increased during indoor exercise, but data on the emission of aerosol particles by an exercising individual are lacking. Here, we report that aerosol particle emission increases on average 132-fold from 580 ± 489 particles/min at rest to 76,200 ± 48,000 particles/min during maximal exercise. Aerosol particle emission increases moderately up to an exercise intensity of ≈2 W/kg and exponentially at higher exercise intensities. These data not only explain SARS-CoV-2 transmissions during indoor group exercise but also can be used to design better targeted mitigation measures for physical activity indoors such as physical education in school, dance events during weddings, or high-intensity gym classes such as spinning.

Many airborne pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are transmitted indoors via aerosol particles. During exercise, pulmonary ventilation can increase over 10-fold, and therefore, exercisers will exhale a greater volume of aerosol-containing air. However, we currently do not know how exercise affects the concentration of aerosol particles in exhaled air and the overall emission of aerosol particles. Consequently, we developed a method to measure in parallel the concentration of aerosol particles in expired air, pulmonary ventilation, and aerosol particle emission at rest and during a graded exercise test to exhaustion. We used this method to test eight women and eight men in a descriptive study. We found that the aerosol particle concentration in expired air increased significantly from 56 ± 53 particles/liter at rest to 633 ± 422 particles/liter at maximal intensity. Aerosol particle emission per subject increased significantly by a factor of 132 from 580 ± 489 particles/min at rest to a super emission of 76,200 ± 48,000 particles/min during maximal exercise. There were no sex differences in aerosol particle emission, but endurance-training subjects emitted significantly more aerosol particles during maximal exercise than untrained subjects. Overall, aerosol particle emission increased moderately up to an exercise intensity of ∼2 W/kg and exponentially thereafter. Together, these data might partly explain superspreader events especially during high-intensity group exercise indoors and suggest that strong infection prevention measures are needed especially during exercise at an intensity that exceeds ∼2 W/kg. Investigations of influencing factors like airway and whole-body hydration status during exercise on aerosol particle generation are needed.