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Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event
Indoor Air
Abstract
During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the aerosol route is likely; it appears unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases. It is vital to identify features of cases such as this to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was dominated by inhalation of respiratory aerosol generated by one index case, we use the available evidence to infer the emission rate of aerosol infectious quanta. We explore how the risk of infection would vary with several influential factors: ventilation rate, duration of event, and deposition onto surfaces. The results indicate a best-estimate emission rate of 970 ± 390 quanta h-1 . Infection risk would be reduced by a factor of two by increasing the aerosol loss rate to 5 h-1 and shortening the event duration from 2.5 to 1 h.
... In another example, a choir rehearsal in the United States in March 2020 resulted in significant airborne transmission, with a single index case potentially infecting 52 secondary cases [23]. The airborne infection rate and R 0 were estimated at 86.7% and 52, respectively. ...
... (An infectious quantum is a hypothetical unit of infectivity derived from epidemiological studies, representing the assembly of viral particles necessary to establish infection.) Upon examining the characteristics of 19 reported cases of airborne SARS-CoV-2 transmission available as of December 2020 ( Table 3) [22][23][24][26][27][28][29][30][31][32][33][34][35][36][37][38], it is evident that indoor environments involving conversation or similar actions (such as oxygen mask usage) tend to exhibit high transmission rates, even over relatively short periods. This pattern is observed in cases such as the karaoke room in China (Case 1) [26], the restaurant in China (Case 2) [22], and the choir rehearsal in the USA (Case 5) [23]. ...
... Upon examining the characteristics of 19 reported cases of airborne SARS-CoV-2 transmission available as of December 2020 ( Table 3) [22][23][24][26][27][28][29][30][31][32][33][34][35][36][37][38], it is evident that indoor environments involving conversation or similar actions (such as oxygen mask usage) tend to exhibit high transmission rates, even over relatively short periods. This pattern is observed in cases such as the karaoke room in China (Case 1) [26], the restaurant in China (Case 2) [22], and the choir rehearsal in the USA (Case 5) [23]. 2024 ...
[Background] The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019 has led to
a global pandemic through contact, droplets, and aerosolized particles.
[Aim] This study aimed to quantify the airborne transmission risk of SARS-CoV-2 in various indoor environments.
[Methods] Using indoor carbon dioxide (CO2) levels, we estimated the probability of airborne transmission and the basic reproduction number (R0) across 10 hypothetical indoor scenarios, including a college classroom, restaurant, classical music concert, live event, city bus, crowded train, hospital room, home, shogi match,and business meeting, using an analysis based on the modified Wells-Riley model.
[Results] The relationship between airborne transmission rates and indoor CO2 concentrations was visualized with and without the use of masks. Without masks, at an indoor CO2 concentration of 1,000 ppm, airborne transmission rates were high in a home (100%), business meeting (100%), and hospital room (95%); however, they were moderate in a restaurant (55%), at a shogi match (22%), and at a live concert (21%); and low in a college classroom (1.7%), on a city bus (1.3%), at a classical music concert (1.0%), and on a crowded train (0.25%). In contrast, R0 was high at a live event (42.3), in a restaurant (15.9), in a home (3.00), and in a
hospital room (2.86), indicating a greater risk of cluster infections. An examination of reduced airborne infection risk through surgical mask use and improved ventilation across various scenarios revealed that mask-wearing was highly effective in hospital rooms, in restaurants, at shogi matches, and in live concerts. Ventilation was particularly useful in hospital rooms, in restaurants, and at shogi matches.
[Discussion and conclusion] In all indoor scenarios, a positive linear relationship existed between airborne transmission risk and indoor CO2 levels. The risk varied markedly across scenarios and was influenced by factors such as mask use, ventilation quality, conversation, and exposure duration. This model indicates that the risk of SARS-CoV-2 airborne transmission can be easily predicted using a CO2 meter.
... The COVID-19 pandemic and related research have provided compelling evidence supporting the prevalence of airborne virus transmission [1]. This mode of transmission is particularly prominent in specific environmental conditions, notably in poorly ventilated indoor spaces [2,3]. Ventilation primarily affects aerosols and not large droplets or surfaces [4,5]. ...
... Ventilation primarily affects aerosols and not large droplets or surfaces [4,5]. A variety of analytical approaches, including epidemiological analyses, airflow model simulations, tracer experiments, and the examination of superspreading events in diverse indoor settings [1,2,6,7], consistently point towards aerosols as the most probable mode of transmission [8]. The transmission is often associated with factors such as indoor settings, crowded environments, extended exposure periods, inadequate ventilation, vocalization, activity level and improper mask usage [1,2,4,5]. ...
... A variety of analytical approaches, including epidemiological analyses, airflow model simulations, tracer experiments, and the examination of superspreading events in diverse indoor settings [1,2,6,7], consistently point towards aerosols as the most probable mode of transmission [8]. The transmission is often associated with factors such as indoor settings, crowded environments, extended exposure periods, inadequate ventilation, vocalization, activity level and improper mask usage [1,2,4,5]. ...
... This paper suggests a complex teaching framework to enhance the rhythmic literacy of choral conductors. This system consists of specific training courses that center on the details of syncopation and anacrusis, the incorporation of digital tools for immediate feedback and interactive learning opportunities, and the use of culturally appropriate teaching strategies that highlight the emotional and storytelling aspects of rhythm (Miller et al., 2020;Silber, 2005). ...
... According to Miller et al. (2020), choral education has developed to improve instruction on intricate rhythms, specifically syncopation and anacrusis. Modern pedagogical methods and technological advances are now integrated with traditional techniques to improve rhythm instruction. ...
... Interactive exercises and immediate feedback are provided by digital tools such as Rhythm Trainer and Smart Music, enhancing rhythmic comprehension (Miller et al., 2020). Interactive practice is made possible with Rhythm Trainer, while Smart Music offers choir members the opportunity to practice their parts alongside the full ensemble. ...
This paper delves into the difficulties of interpreting complex rhythmic elements like syncopation and anacrusis in Ghanaian art music, particularly in choral presentations. Syncopation changes the stress on typically less prominent beats, increasing intricacy and intensifying emotional richness. Anacrusis, also known as lead-in notes, establishes the emotional atmosphere, directs the speed, and involves the listeners. Nevertheless, numerous choral conductors face difficulties with these components because of their limited grasp on rhythm, resulting in performances that are lacking in emotional impact and cultural authenticity. This paper suggests educational approaches, such as specific instruction and technology, to improve rhythmic proficiency in choir conductors. Based on a thorough review of literature, the research highlights the significance of precise rhythm in maintaining the emotional impact and cultural identity of Ghanaian art music. The paper suggests using a mix of traditional and modern methods in teaching to enhance choral directors' interpretation abilities.
... Central to it is the number of infectious quanta emitted by infected people. An overwhelming majority of models [5][6][7][8]9], developed during the COVID-19 pandemic to estimate appropriate ECA delivery rates, used the Wells-Riley model and a deterministic value of the quantum emission rate from reported outbreaks of the disease. Outbreak data can be used to model what-if scenarios for the same outbreak. ...
... The viral load can be obtained from NP swabs using real time reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis and is inferred from a cycle threshold [14]. RT-qPCR analysis assumes a direct correlation between the viral load of a swab and the viral load of respiratory fluid [25,8]. It is a semi-quantitative method because the amount of virus on a swab is normally too low for immediate detection and so it requires a number of amplification cycles to provide a positive signal of the virus genome. ...
... The quantum emission rate, q i , for SARS-CoV-2 is predicted by the model to have a confidence interval of 95 % CI[1.4 × 10 −5 , 7.0] quanta h −1 , which shows that the uncertainty in its value is likely to be around 6 orders of magnitude most of the time. The upper interval may seem low when compared to those reported for some superspreading events; for example, the 970 ± 390 quanta h −1 reported by Miller et al. [8] and the median 130 quanta h −1 reported by Log-normal GM = 1.5 × 10 5 GSD = 1.1 [47,35] Respiratory particle evaporation factor, E Beta α = 2.0, β = 5.0 = min 2.0, = max 5.0 [48] Mean respiratory particle diameter, d (m) Log-normal GM = 1.9 × 10 −6 GSD = 1.1 [35] Genomic viral load † , L g (log 10 RNA copies ml −1 ) Normal μ = 7.0, σ = 1.4 [24] Viable fraction, v Beta α = 2.0, β = 5.0 = min 10 4 , = max 10 2 [12] Respiratory tract absorption fraction, k Uniform = min 0.43, = max 0.65 [49] Dose constant, K Uniform = min 5.0, = max 15 [12] μ, mean; σ, standard deviation. GM, geometric mean; GSD, geometric standard deviation; α and β are shape parameters. ...
... For many years, quanta generation rates have been estimated using outbreak data based on the Wells-Riley equation [34]. Typically, values between 30 and 1000 quanta/h have been estimated for SARS-CoV-2 [29,31]. In most studies of potentially airborne outbreaks of respiratory infection, there has been a lack of ventilation rate measurement, possibly due to difficulties in full access to the involved venues and the lack of a simple but effective measurement method. ...
... Our simple three-zone model estimate suggests that the likely quanta generation rate was 1968 quanta/h, which may be the highest quanta generation rate observed to date; to our best knowledge, it is higher than any reported value in the literature [27,29,31,42]. Due to the predominant airflows from Zone C to B and the large equivalent dilution air flow rate in Zone C, the quanta concentration was relatively low in Zone C. ...
The lack of knowledge on quanta generation rates presents a major obstacle to specifying the minimum ventilation required to prevent airborne infections. The expected largest quanta generation rate of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by a super-spreader remains unknown. Here we investigated a SARS-CoV-2 outbreak during lunch in a restaurant using epidemiological, whole-genome sequencing and environmental analyses. Both tracer gas and fine particles were used in field experiments to quantify aerosol dispersion and removal across three interconnected zones: Zone A, Zone B and Zone C. All 21 secondary patron infections occurred in Zone B. This unique infection feature and measured dilution flow rates allowed us to estimate the largest reported quanta generation rates to date, ranging from 1724 to 1968 quanta/h. These rates were sufficiently high to cause a high attack rate in Zone B but did not cause infections in Zones A and C, likely due to sufficient dilution and insignificant contaminated airflow from Zone B, respectively. Our finding of the largest quanta generation rate so far suggests that avoiding secondary infection by dilution alone in the presence of a super-emitter might not be possible in typical air-conditioned buildings and other prevention strategies need to be developed.
... In order to address these challenges, simple yet insightful models, such as the well-mixed model (Wells et al 1955, Riley et al 1978, Bazant and Bush 2021, have been applied within the context of airborne contagion. These models aim to estimate the concentration of particles, and consequently the risk of infection, by additionally taking into consideration viral properties and physiological factors (Buonanno et al 2020, Sun and Zhai 2020, Bazant and Bush 2021, Miller et al 2021. From a fluid mechanics point of view, the well-mixed model operates under the assumption that the ejected droplet nuclei instantly and uniformly disperse throughout the indoor area. ...
... For an indoor space of volume V , the time-dependent normalized nuclei concentration for nuclei of radius r may be expressed as (Wells et al 1955, Riley et al 1978, Bazant and Bush 2021, Miller et al 2021, Salinas et al 2022 ...
We conduct large eddy simulations in a canonical room of size 10m*10m*3.2m subject to mechanical ventilation to assess the impact of internal heating on droplet nuclei dispersal in indoor spaces. We conduct two simulations with a solitary heat source placed at the center of the room in the first, and 16 heat sources arranged in an equidistant non-staggered formation in the second. The heat sources
mimic heat generation from an adult person. The simulations employ a statistical overloading approach where 10 million droplet nuclei are individually monitored for approximately one hour in real-time. These results are then compared to previous simulations that share identical setup and procedures but do not account for any thermal load. We assess the effect of internal heat sources on
multiple levels by averaging over all possible positions of the infected (source) and the susceptible (sink) occupants within the room. We find that, at the room-average level, the room concentration, which results from a balance of droplet nuclei production through expiratory events and removal through various mechanisms is unaffected by the presence of heat sources. On the other hand,
the spatial and temporal dispersion of droplet nuclei, as observed from the standpoint of a known source or sink location, or when a combination of sources and sinks at fixed separation distances is considered, is significantly influenced by the presence of heat sources.
... In the model setup, altogether 11 attendees are located in the room as heat sources. The number of attendees (11) in the computational model was chosen based on the number of participants attending the study. We assume a heat load that goes to the thermal plumes of each singer, while the heat radiation effects are neglected since they are considered significantly less important to the overall flow field structure. ...
... The figure displays i) the hypothesized index person (singer 3) releasing viruses at the corner of the room, ii) two inflow air jets entering from the elongated gaps of width 0.2 m symmetrically from opposite ends of the room, iii) the outflow air exhaust, which consists of two symmetric air gaps of width 0.2 m in the center of the room, and iv) two radiators located at the opposing walls. The choir leader (11) and the accordionist (10) are also marked in the figure. The simulation starts from time t = 0 during which the flow field is fully developed while q = 0 everywhere in the room. ...
Introduction
COVID-19 pandemic has highlighted the role of aerosol transmission and the importance of superspreading events. We analyzed a choir rehearsal in November 2020, where all participants, except one who had recently earlier recovered from COVID-19, were infected. We explore the risk factors for severe disease in this event and model the aerosol dispersion in the rehearsal room.
Materials and methods
Characteristics of participants were collected by interviews and supplemented with patient records. A computational simulation of aerosol distribution in the rehearsal room and the efficacy of potential safety measures was conducted using the Large-Eddy Simulation approach. Infection risk was studied by analyzing quanta emission and exposure with the Wells-Riley equation.
Results
The simulation showed that airborne transmission likely explains this mass contagion event. Every singer was exposed to the virus in only 5 min from the beginning of the rehearsal, and maximum concentration levels were reached at 20 min the concentration levels started to approach a steady state after 20 min. Although concentration differences existed in the room, risk levels near (1 m) and far (5 m) from the aerosol source were similar for certain singers. Modeling indicated infection risk levels of 70–100% after one hour; the risk would have been considerably reduced by wearing high-filtration respirators. Age and pre-existing comorbidities predicted more severe disease. The high incidence of illness may be partly attributed to the relatively high median age of individuals. Additionally, those admitted to the hospital had multiple underlying health conditions that predispose them to more severe disease.
Conclusions
Airborne transmission and indoor space can explain this mass exposure event. High-filtration respirators could have prevented some infections. The importance of safety distances diminishes the longer the indoor event. The concept of safety distance is challenging, as our study suggests that long range airborne transmission may occur in indoor events with extended duration. We encourage informing the public, especially persons at risk, of safety measures during epidemics.
... [9]. Multiple studies have reported airborne transmission of coronavirus disease (COVID-19), particularly in poorly ventilated indoor spaces [10][11][12][13][14][15]; hence, the application of CO 2 concentration as an indicator of risk for the airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has also been proposed [16,17]. ...
... Outbreaks due to airborne transmission during choruses have been confirmed in the U.S. and Australia [13,39]. Clusters also occurred during yoga sessions in poorly ventilated gyms in South Korea [40]. ...
We employed carbon dioxide (CO2) concentration monitoring using mobile devices to identify location-specific risks for airborne infection transmission. We lent a newly developed, portable Pocket CO2 Logger to 10 participants, to be carried at all times, for an average of 8 days. The participants recorded their location at any given time as cinema, gym, hall, home, hospital, other indoors, other outgoings, pub, restaurant, university, store, transportation, or workplace. Generalized linear mixed model was used for statistical analysis, with the objective variable set to the logarithm of CO2 concentration. Analysis was performed by assigning participant identification as the random effect and location as the fixed effect. The data were collected per participant (seven males, four females), resulting in a total of 12,253 records. Statistical analysis identified three relatively poorly ventilated locations (median values > 1,000 ppm) that contributed significantly (p < 0.0001) to CO2 concentrations: homes (1,316 ppm), halls (1,173 ppm), and gyms (1005ppm). In contrast, two locations were identified to contribute significantly (p < 0.0001) to CO2 concentrations but had relatively low average values (<1,000 ppm): workplaces (705 ppm) and stores (620 ppm). The Pocket CO2 Logger can be used to visualize airborne infectious transmission risk by location to help guide recommendation regarding infectious disease policies, such as restrictions on human flow and ventilation measures and guidelines. In the future, large-scale surveys are expected to utilize the global positioning system, Wi-Fi, or Bluetooth of an individual’s smartphone to improve ease and accuracy.
... where r DOUT is the virus emission rates from the infected person, B is Miller et al., 2021), t R is the exposure time (h); τ D is the time constant for viral inactivation (0.32 h − 1 ), τ VF is the ventilation rate (h − 1 ), τ F is the deposition rate (0.3 h − 1 ), and V R is the volume of the indoor environment (m 3 ). The accurate volume of the indoor environment is provided by the cruise company (Table 2) and the ventilation rate in ACH (τ VF ) is estimated with occupancy and CO 2 concentration monitored (Section 3.4). ...
... The pathogen of interest was SARS-CoV-2 since this was used in a previous RRTO survey to inform estimated infection risks from contaminated surfaces (Wilson et al. 2022b). While fomites do not pose the greatest transmission risk for SARS-CoV-2 (Jones 2020; Centers for Disease Control and Prevention 2021; Miller et al. 2021;Pitol and Julian 2021;Wilson et al. 2021aWilson et al. , 2021b, COVID-19 transmission via fomites (hand-to-contaminated surface contact followed by hand-to-mouth contact) has been documented (Xie et al. 2020) with potential for transmission through contact with the eyes (Eriksen et al. 2021) and nose (Ahn et al. 2021) and has spurred recent increases in cleaning and disinfection exposure (Kuehn 2020;Wilson et al. 2023a). Other pathogens could be substituted to investigate how specific pathogens or their associated health outcomes drive RRTO indifference points and critical concentrations. ...
... We found that four of the tools from Table 1 were retrospectively assessed against reported transmission events, namely the COVID-19 Aerosol Transmission Risk Calculator (Lelieveld et al., 2020), the COVID-19 Aerosol Transmission Estimator (Peng et al., 2022), the WHO ARIA tool (World Health Organization, 2024) and the Airborne Infection Risk Calculator (Mikszewski et al., 2021). Interestingly, all tools were retrospectively assessed for the same widely reported outbreak of SARS-CoV-2 at a choir rehearsal of the Skagit Valley Chorale (SVC) in March 2020 (Miller et al., 2021). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died, yielding an infection risk of 87%. ...
... increased, aerosol transmission emerged as the dominant form of SARS-CoV-2 spread [2][3][4]. Airborne viruses are believed to predominantly exist inside aerosolized particles of moisture emitted from the upper respiratory tract of infected persons through not only coughing, but speaking [3], singing [5], and even breathing [6]. Coughing is known to produce many larger, heavier droplets (diameter >10 μm) [7], while speaking, singing, and breathing are more likely to produce aerosols (defined here as diameter <10 μm) [3]. ...
The COVID-19 pandemic highlighted the role of indoor environments on disease transmission. However, our understanding of how transmission occurred evolved as the pandemic progressed. Enclosed spaces where pathogen-laden aerosols accumulate were strongly linked to increased transmission events. Most classrooms, particulalry in the U.S., do not have any mechanical ventilation systems but do have many people congregating indoors for long periods of time. Here we employ a safe, non-pathogenic surrogate virus, the bacteriophage phi6, to interrogate aerosol transmission in classroom environments that do not have any natural or mechanical ventilation in order to provide baseline understanding of how effectively aerosols facilitate new infections. We measure exposure risk using a modified passive monitoring technique compliant with applicable standards, including ISO 14698–1:2003. We find that virus-laden aerosols establish new infections over all distances tested within minutes and that the time of exposure did not change transmission rate. We further find that relative humidity, but not temperature nor a UV-based disinfection device, significantly lowered transmission rates. Our data suggest that, even without mechanical ventilation, relative humidity remains an inexpensive and highly effective mitigation strategy while UV air treatment may not.
... supermarkets). In addition, most models either neglect the physics of the spread of infectious aerosols 8,9,11,12,15,16 , or use computational fluid dynamics simulations 6,10,14 , making them too computationally intensive for fast policymaking. Here, building on research Kaouri and Woolley used to inform policy during the pandemic 4,5 , we present VIRIS, a new simulator and a web app that incorporates both people movement and aerosol physics in geometrically complex, architecturally defined spaces, providing solutions with great speed. ...
A Viral Infection Risk Indoor Simulator (VIRIS) has been developed to quickly assess and compare mitigations for airborne disease spread. This agent-based simulator combines people movement in an indoor space, viral transmission modelling and detailed architectural design, and it is powered by topologicpy, an open-source Python library. VIRIS generates very fast predictions of the viral concentration and the spatiotemporal infection risk for individuals as they move through a given space. The simulator is validated with data from a courtroom superspreader event. A sensitivity study for unknown parameter values is also performed. We compare several non-pharmaceutical interventions (NPIs) issued in UK government guidance, for two indoor settings: a care home and a supermarket. Additionally, we have developed the user-friendly VIRIS web app that allows quick exploration of diverse scenarios of interest and visualisation, allowing policymakers, architects and space managers to easily design or assess infection risk in an indoor space.
... Both large-and small-scale events were assumed to increase the risk of virus transmission and thus amplifying the burden of the pandemic. In fact, there are many reports of transmission events in confined and poorly ventilated indoor spaces, partly due to infectious aerosols 4,5 . However, recent studies have shown that the eventrelated risk of contracting SARS-CoV-2 can kept very low with wellfunctioning ventilation systems and appropriate mitigation strategies to reduce exposure to infectious aerosols [6][7][8][9] . ...
The COVID-19 pandemic demonstrated that reliable risk assessment of venues is still challenging and resulted in the indiscriminate closure of many venues worldwide. Therefore, this study used an experimental, numerical and analytical approach to investigate the airborne transmission risk potential of differently ventilated, sized and shaped venues. The data were used to assess the magnitude of effect of various mitigation measures and to develop recommendations. Here we show that, in general, positions in the near field of an emission source were at high risk, while the risk of infection from positions in the far field varied depending on the ventilation strategy. Occupancy, airflow rate, residence time, virus variants, activity level and face masks affected the individual and global infection risk in all venues. The global infection risk was lowest for the displacement ventilation case, making it the most effective ventilation strategy for keeping airborne transmission and the number of secondary cases low, compared to mixing or natural ventilation.
... 16 For example, infectious virus, such as SARS-CoV-2, 17,18 Middle East respiratory virus (MERS), 19 influenza, 20,21 and respiratory syncytial virus (RSV), 22 as well as nucleic acids from SARS-CoV-1, 23 rhinovirus, 24 and measles virus 25 can be recovered in air samples from infected patients. Furthermore, experimental 26 and epidemiological data from humans [27][28][29][30][31][32][33] and data from animal studies 34-38 confirm a substantial role for these infectious aerosols in transmitting clinical disease. Bacterial diseases, such as pulmonary tuberculosis, caused by Mycobacterium tuberculosis, can also be spread by airborne transmission, as demonstrated in experiments where guinea pigs exposed to air from hospital tuberculosis wards, but not unexposed animals, became infected. ...
The importance of aerosols (particles suspended in air) produced during dental procedures became more apparent than ever during the COVID-19 pandemic. Concerns over transmission of infection in these aerosols led to unprecedented disruption to dental services across the world, adversely impacting patients’ oral health. This article discusses the evidence related to airborne transmission of infectious diseases and the relevance to dentistry. The production of bioaerosols (aerosols carrying biological material) during dental procedures is explored, as well as how the potential risks posed by these bioaerosols can be controlled. A better understanding of dental bioaerosols is needed to prevent similar disruption to dental services in future outbreaks, and to reduce the risk of infection of dental professionals when treating patients with active infections who require urgent or emergency dental care.
... An increasing number of studies have recognised airborne transmission as the predominant route for the spread of respiratory diseases, such as COVID-19 and influenza [18,26,40]. Many studied outbreaks have revealed the long-range airborne transmission of respiratory pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [21,25,30], influenza viruses [38], SARS-CoV [17], and Middle East respiratory syndrome coronavirus [41]. Most infections with such respiratory pathogens occur indoors, e.g. ...
... (e.g., Randall et al., 2021), virus-containing aerosol particles are now thought to be a major vehicle for spreading respiratory diseases, including influenza and COVID-19 (Coronavirus disease 2019; Chen et al., 2020;Greenhalgh et al., 2021;Miller et al., 2021). Numerous epidemiological studies have pointed to the importance of environmental conditions on the stability of airborne viruses (e.g., Hanley and Borup, 2010;Deyle et al., 2016;Sehra et al., 2020). ...
We describe a novel biosafety aerosol chamber equipped with state-of-the-art instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of relative humidity (RH) in very clean air without trace gases (except ∼400 ppm CO2) on the preservation of influenza A virus (IAV) infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, t99, a metric we consider most relevant to airborne virus transmission. The viruses remained infectious for a long time, namely t99 > 5 h, if RH < 30% and the particles effloresced. Under intermediate conditions of humidity (40% < RH < 70%), the loss of infectivity was the most rapid (t99 ≈ 15–20 min, and up to t99 ≈ 35 min at 95% RH). This is more than an order of magnitude faster than suggested by many previous studies of aerosol-borne IAV, possibly due to the use of matrices containing organic molecules, such as proteins, with protective effects for the virus. We tested this hypothesis by adding sucrose to our aerosolization medium and, indeed, observed protection of IAV at intermediate RH (55%). Interestingly, the t99 of our measurements are also systematically lower than those in 1-μL droplet measurements of organic-free saline solutions, which cannot be explained by particle size effects alone.
... be transmitted by aerosols in various locations, such as hospitals 6,13 , community settings 14 , public transportation 15,16 , schools 17,18 , bars 17 , and gymnasiums 18 , even causing so-called "super-spreading events" 19,20 . As a result, deploying rapid and sensitive surveillance devices for monitoring contagious bioaerosols in highly crowded places has been gradually regarded as an efficient and non-invasive means to contain the disease spreading without interrupting normal social activities 21,22 . ...
Highly sensitive airborne virus monitoring is critical for preventing and containing epidemics. However, the detection of airborne viruses at ultra-low concentrations remains challenging due to the lack of ultra-sensitive methods and easy-to-deployment equipment. Here, we present an integrated microfluidic cartridge that can accurately detect SARS-COV-2, Influenza A, B, and respiratory syncytial virus with a sensitivity of 10 copies/mL. When integrated with a high-flow aerosol sampler, our microdevice can achieve a sub-single-copy spatial resolution of 0.83 copies/m³ for airborne virus surveillance with an air flow rate of 400 L/min and a sampling time of 30 minutes. We then designed a series of virus-in-aerosols monitoring systems (RIAMs), including versions of a multi-site sampling RIAMs (M-RIAMs), a stationary real-time RIAMs (S-RIAMs), and a roaming real-time RIAMs (R-RIAMs) for different application scenarios. Using M-RIAMs, we performed a comprehensive evaluation of 210 environmental samples from COVID-19 patient wards, including 30 aerosol samples. The highest positive detection rate of aerosol samples (60%) proved the aerosol-based SARS-CoV-2 monitoring represents an effective method for spatial risk assessment. The detection of 78 aerosol samples in real-world settings via S-RIAMs confirmed its reliability for ultra-sensitive and continuous airborne virus monitoring. Therefore, RIAMs shows the potential as an effective solution for mitigating the risk of airborne virus transmission.
... Viruses in aerosols with a size smaller than 100 µm can remain suspended in the air for three hours [12], increasing the risk of infecting others. Infectious viruses carried by aerosols can travel distances greater than 2 m, leading to their accumulation in indoor space and leading to super-spreading events [13]. For this reason, we wanted to examine the prevalence of detectable SARS-CoV-2 in spaces where students congregate, talk, and exercise in the time period after vaccination was widely available and constraints on the use of indoor spaces had largely been lifted. ...
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spreads primarily through respiratory droplets, aerosols, and contaminated surfaces. While high-traffic locations like hospitals and airports have been studied extensively, detecting significant virus levels in aerosols and on environmental surfaces, campus settings remain underexplored. This study focused on two crowded buildings at the University of North Carolina at Charlotte (UNCC). From December 2021 to March 2022, we collected 16 indoor air samples and 201 samples from high-touch surfaces. During the sampling timeframe, 44.82% of surface samples from the Student Union and 28% from the University Recreational Center (UREC) tested positive for the presence of SARS-CoV-2 RNA. Median and average viral RNA copies per swab were higher in UREC (273 and 475) than in Student Union (92 and 269). However, all air samples tested negative. Surface positivity in these high-traffic campus locations was directly correlated with COVID-19 clinical cases in Mecklenburg County. The campus COVID-19 cases, driven by the Omicron wave, peaked a week before the peak detection of surface contamination. These findings underscore the importance of surface hygiene measures and highlight environmental conditions as potential contributors to COVID-19 spread on campuses.
... Fine particulate matter can also adsorb viral particles, potentially enhancing the virus's stability and spread (77). Studies have shown that improved ventilation and air cleaning significantly reduce airborne viral loads, thereby mitigating the risk of transmission within enclosed spaces (80,81). Effective ventilation, whether through natural means like opening windows or mechanical systems, helps disperse and dilute viral particles, reducing their potential to infect new hosts. ...
The coronavirus disease 2019 (COVID-19) pandemic underscores the critical need to integrate immunomics within the One Health framework to effectively address zoonotic diseases across humans, animals, and environments. Employing advanced high-throughput technologies, this interdisciplinary approach reveals the complex immunological interactions among these systems, enhancing our understanding of immune responses and yielding vital insights into the mechanisms that influence viral spread and host susceptibility. Significant advancements in immunomics have accelerated vaccine development, improved viral mutation tracking, and broadened our comprehension of immune pathways in zoonotic transmissions. This review highlights the role of animals, not merely as carriers or reservoirs, but as essential elements of ecological networks that profoundly influence viral epidemiology. Furthermore, we explore how environmental factors shape immune response patterns across species, influencing viral persistence and spillover risks. Moreover, case studies demonstrating the integration of immunogenomic data within the One Health framework for COVID-19 are discussed, outlining its implications for future research. However, linking humans, animals, and the environment through immunogenomics remains challenging, including the complex management of vast amounts of data and issues of scalability. Despite challenges, integrating immunomics data within the One Health framework significantly enhances our strategies and responses to zoonotic diseases and pandemic threats, marking a crucial direction for future public health breakthroughs.
... To experimentally study the airborne transmission of pathogens, one of the most challenging parts is to find suitable surrogates for the infectious particles that are emitted from the infected people. Tracer gases, such as CO 2 [23,24], SF 6 [25][26][27][28], N 2 O [29], and ethane [30], are commonly used because they involved simpler measuring instruments and the sources are more controllable compared to using tracer particles [31]. However, pathogens are biological particles, which have an important feature that they deposit on surfaces at rates (dominated by particle sizes) could be far different from tracer gases [32]. ...
The effects of ceiling fans on the transmission of infectious aerosols remain poorly understood, leading to conflicting recommendations. We conducted repeated experiments in a well-controlled chamber with a typical mixing ventilation system at three different ventilation rates with and without ceiling fans. We evaluated airborne infection risks for short- and long-range transmission routes based on size-resolved tracer particles measured at various locations. We found that the mixing ventilation without fans only effectively diluted the airborne particle concentration for the long-range route but not for the short-range. By using ceiling fans to enhance air mixing, tracer particles were distributed more homogeneously throughout the room, leading to up to 77 % reduction in short-range particle exposure while a slight increase of less than 14 % in long-range exposure. Based on the dilution-based Wells-Riley model, the changes in particle concentration translated to a maximum 47 % reduction in short-range infection risk and a marginal 4 % increase for long-range transmission. Based on the dilution factors obtained from the experiments, we developed a decision-making tool that uses the ventilation rate, the number of individuals at short- and long-range, and the disease's transmissibility to decide whether the use of ceiling fans is beneficial. Deploying ceiling fans always reduces the concentration of particles in the short range and, assuming a relationship between particles and pathogens, this directly translates to a diminished short-range risk. Based on the modeling of the overall risk, the benefits of fans are highest when the room is ventilated according to code, when masking measures are in place, and when the pathogen is not highly contagious.
... A growing body of evidence has recognized the "airborne transmission" or "aerosol transmission"-where persistent aerosols emitted by an infected person can stay airborne and be subsequently breathed in by others-as a major pathway of SARS-CoV-2 transmission [1][2][3]. In addition, some studies have shown that the risk of transmission indoors can be orders of magnitude higher than in outdoor environments [4]. ...
Educational buildings tend to fail in the contagion containment of airborne infectious diseases because of the high number of children, for several hours a day, inside enclosed environments that often have inadequate indoor air quality (IAQ) conditions. This study aimed to assess indoor environmental quality and test the effectiveness of portable air cleaners (PACs) in alleviating airborne particle levels in schools of Central–Southern Spain during the period of reopening after the lockdown due to the COVID-19 outbreak. To accomplish this, three sampling campaigns were organized from September to December 2020 to consistently monitor temperature and relative humidity, carbon dioxide, and particulate matter in nineteen classrooms (seven school buildings). Results showed that although the recommendation of maintaining the windows open throughout the day seemed to be effective in promoting, in general, proper ventilation conditions (based on CO2 levels). For the colder campaigns, this practice caused notorious thermal comfort impairment. In addition, a great number of the surveyed classrooms presented levels of PM2.5 and PM10, attributable to outdoor and indoor sources, which exceeded the current WHO guideline values. Moreover, considering the practice of having the windows opened, the installation of 1 unit of PACs per classroom was insufficient to ensure a reduction in particle concentration to safe levels. Importantly, it was also found that children of different ages at different education levels can be exposed to significantly different environmental conditions in their classrooms; thus, the corrective measures to employ in each individual educational setting should reflect the features and needs of the target space/building.
... The secondary attack rates ranged from 4.32% to 100.00% Hsu et al., 2022). The cases were from January 2020 to November 2022 Luo et al., 2020;Shen et al., 2020;Xiang et al., 2023), which was mostly distributed in 2020 (Bays et al., 2021;Deng et al., 2021;Hijnen et al., 2020;Huang et al., 2022;Khanh et al., 2020;Kriegel et al., 2021;Kwon et al., 2020;Li et al., 2022;Luo et al., 2020;Miller et al., 2021;Park et al., 2020;Reichert et al., 2022;Shen et al., 2020;Stein-Zamir et al., 2020;Sun & Zhai, 2020;Vernez et al., 2021;Zhao et al., 2021). The criteria for our case selection are as follows: 1. ...
We constructed a rapid infection risk assessment model for contacts of COVID‐19. The improved Wells–Riley model was used to estimate the probability of infection for contacts of COVID‐19 in the same place and evaluate their risk grades. We used COVID‐19 outbreaks that were documented to validate the accuracy of the model. We analyzed the relationship between controllable factors and infection probability and constructed common scenarios to analyze the infection risk of contacts in different scenarios. The model showed the robustness of the fitting (mean relative error = 5.89%, mean absolute error = 2.03%, root mean squared error = 2.03%, R² = 0.991). We found that improving ventilation from poorly ventilated to naturally ventilated and wearing masks can reduce the probability of infection by about two times. Contacts in places of light activity, loud talking or singing, and heavy exercise, oral breathing (e.g., gyms, KTV, choirs) were at higher risk of infection. The model constructed in this study can quickly and accurately assess the infection risk grades of COVID‐19 contacts. Simply opening doors and windows for ventilation can significantly reduce the risk of infection in certain places. The places of light activity, loud talking or singing, and heavy exercise, oral breathing, should pay more attention to prevent and control transmission of the epidemic.
... Recent studies have also provided evidence linking aerosols to outbreaks in small and crowded environments such as classrooms, churches, and restaurants (Buonanno et al., 2022;Miller et al., 2021). High concentrations of aerosols containing the influenza-A virus were detected at various locations on a university campus during an influenza-A outbreak (Ramuta et al., 2022). ...
The development of effective methods for the surveillance of seasonal respiratory viruses is required for the timely management of outbreaks. We aimed to survey Influenza‐A, Influenza‐B, RSV‐A, Rhinovirus and SARS‐CoV‐2 surveillance in a tertiary hospital and a campus over 5 months. The effectiveness of air screening as an early warning system for respiratory viruses was evaluated in correlation with respiratory tract panel test results. The overall viral positivity was higher on the campus than in the hospital (55.0% vs. 38.0%). Influenza A was the most prevalent pathogen in both locations. There were two influenza peaks (42nd and 49th weeks) in the hospital air, and a delayed peak was detected on campus in the 1st‐week of January. Panel tests indicated a high rate of Influenza A in late December. RSV‐A‐positivity was higher on the campus than the hospital (21.6% vs. 7.4%). Moreover, we detected two RSV‐A peaks in the campus air (48th and 51st weeks) but only one peak in the hospital and panel tests (week 49). Although rhinovirus was the most common pathogen in panel tests, rhinovirus positivity was low in air samples. The air screening for Influenza‐B and SARS‐Cov‐2 revealed comparable positivity rates with panel tests. Air screening can be integrated into surveillance programs to support infection control programs for potential epidemics of respiratory virus infections except for rhinoviruses.
... Subsequently, different studies debated on the importance of the role played by respiratory particles smaller than 5 μm in diameter [25] in the transmission of SARS-CoV-2 and, therefore, in the spread of COVID-19 [26][27][28][29][30][31][32]. In addition to this, different super-spreading events [33][34][35][36] supported aerosols as an important route of SARS-CoV-2 transmission. The WHO later recognized that airborne transmission through aerosols remaining in the air as a possible route of contagion [37]. ...
Since its emergence, the COVID-19 pandemic has profoundly and extensively affected global health and society. Numerous studies have focused on detecting SARS-CoV-2 in air samples collected in healthcare indoor spaces, but few have analysed its presence in air samples from other public community spaces. In addition, limited studies have surveyed indoor spaces where it was not known if individuals with COVID-19 were present or had been present at the time of sampling. This study aimed to determine the SARS-CoV-2 genetic load in aerosol samples collected in public community indoor environments where prior knowledge of the presence of infected individuals with COVID-19 cases is not available at the time of sampling.
Air samples (N = 497) were collected from healthcare settings, elderly care homes, and educational settings in the Valencian Community, Spain. RNA was extracted and the N1, N2, and E gene fragments of SARS-CoV-2 were quantified using RT-qPCR. SARS-CoV-2 RNA was detected in 8.9 % of air samples. The highest positivity rates were observed in hospitals (16.2 %), elderly care homes (15.3 %), and primary care centres (12.7 %). Concentration of the N1 gene in positive samples ranged 4.3–504 gc/m3 (n = 10), 6.2–77 gc/m3 (n = 8) and 5.1–14 gc/m3 (n = 7), respectively. The genes N2 and E were less frequently detected and generally reported lower concentrations.
The frequency of detection of SARS-CoV-2 in aerosols increased at the same time that the population COVID-19 cumulative incidence increased.
... This behavior was initially modeled by Wells and Riley in Wells (1955) and Riley et al. (1978), wherein they describe airborne transmission of infectious aerosols in indoor spaces. The Wells-Riley model has been extensively used (Miller et al. 2021;Buonanno et al. 2020;Prentiss et al. 2020;Evans 2020) to estimate the risk of infection of respiratory diseases in indoor spaces because it includes several parameters, such as the number of occupants and their respiratory activity levels, exposure time, dimensions of the space, types of ventilation and air filtration, mask efficiency, among others. ...
The COVID-19 pandemic brought significant consequences on healthcare systems, economy, and politics. Nowadays, we know that the pathogen responsible for COVID-19 is transmitted mainly by aerosol droplets exhaled by infected individuals, which remain suspended in indoor air. There has been widespread interest in monitoring the C O 2 levels in indoor spaces since an infected patient exhales C O 2 and infectious aerosols when breathing. So, we designed and built an Air Quality Monitoring Device (AQMD) that measures and analyzes the levels of C O 2 and particulate matter in the classrooms of a university with the aim of mitigating the spread of COVID-19. We divided the AQMD design into 2 phases: (i) data measurement and (ii) estimation of infection risk. Specifically, we measured the air quality in 3 classrooms of a university during different types of activities. Using these data, we calculated the recommended C O 2 threshold for our classroom setting and estimated the probability of COVID-19 infection of a susceptible person. Our research shows that indoor C O 2 concentrations and the probability of COVID-19 infection are influenced mainly by the type of activity and the number of windows open; besides, the number of students does not significantly impact the indoor C O 2 concentrations levels because the range of students in the test scenario (18 to 31) was relatively small.
... On a flight from Singapore to Hangzhou, the overall attack rate among passengers was 4.8% [6]. In the Skagit Valley Chorale, 53 of the 61 people in attendance were confirmed or highly suspected to have COVID-19, and two people passed away [7]. These investigations have demonstrated that it is challenging to prevent airborne transmission, especially for people who are in close proximity for an extended period. ...
... (e.g., Randall et al., 2021), virus-containing aerosol particles are now thought to be a major vehicle for spreading respiratory diseases, including influenza and COVID-19 (Coronavirus disease 2019; Chen et al., 2020;Greenhalgh et al., 2021;Miller et al., 2021). Numerous epidemiological studies have pointed to the importance of environmental conditions on the stability of airborne viruses (e.g., Hanley and Borup, 2010;Deyle et al., 2016;Sehra et al., 2020). ...
We describe a novel biosafety aerosol chamber equipped with state-of-the-art instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of relative humidity (RH) in very clean air without trace gases (except ∼400 ppm CO 2 ) on the preservation of influenza A virus (IAV) infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, t 99 , a metric we consider most relevant to airborne virus transmission. The viruses remained infectious for a long time, namely t 99 > 5 h, if RH < 30% and the particles effloresced. Under intermediate conditions of humidity (40% < RH < 70%), the loss of infectivity was the most rapid ( t 99 ≈ 15-20 min, and up to t 99 ≈ 35 min at 95% RH). This is more than an order of magnitude faster than suggested by many previous studies of aerosol-borne IAV, possibly due to the use of matrices containing organic molecules, such as proteins, with protective effects for the virus. We tested this hypothesis by adding sucrose to our aerosolization medium and, indeed, observed protection of IAV at intermediate RH (55 %). Interestingly, the t 99 of our measurements are also systematically lower than those in 1-μL droplet measurements of organic-free saline solutions, which cannot be explained by particle size effects alone.
... In contrast to superspreader events, where only very few (ca. 0.1%) of the aerosols emitted by the index case are inhaled by any given participant [20], all droplets generated by snoring travel into the LRT where they potentially contribute to self-infection. Moreover, in contrast to partial virus inactivation from dehydration in the atmosphere [21], as applies for person-to-person transmission, virions in snoring droplets are not subject to such inactivation during their short path into the high humidity LRT, further increasing the risk of self-infecting the lung. ...
The soft palate and back of the throat represent vulnerable early infection sites for SARS-CoV-2, influenza, streptococci, and many other pathogens. We demonstrate that snoring causes aerosolization of pharyngeal fluid that covers these surfaces, which previously has escaped detection because the inspired airstream carries the micron-sized droplets into the lung, inaccessible to traditional aerosol detectors. While many of these droplets will settle in the lower respiratory tract, a fraction of the respirable smallest droplets remains airborne and can be detected in exhaled breath. We distinguished these exhaled droplets from those generated by the underlying breathing activity by using a chemical tracer, thereby proving their existence. The direct transfer of pharyngeal fluids and their pathogens into the deep lung by snoring represents a plausible mechanistic link between the previously recognized association between sleep-disordered breathing and pneumonia incidence.
... 34 While airborne transmission is not thought to be the primary mode of transmission, it can contribute to the spread of the virus and has led to outbreaks in certain settings, such as choir practices or indoor fitness classes. 35 To reduce the risk of airborne transmission of COVID-19, it is important to reduce the number of virus particle within the air, 36 as a key tool in controlling the spread of the virus and reducing the risk of severe illness and death. 37 This has led to a deeper understanding of the potential for airborne transmission and the need for effective preventive measures. ...
COVID-19 has become a global pandemic that has affected millions of people worldwide. The disease is caused by the novel coronavirus that was first reported in Wuhan, China, in December 2019. The virus is highly contagious and can spread from person to person through respiratory droplets when an infected person coughs, sneezes, talks, or breathes. The symptoms of COVID-19 include fever, cough, and shortness of breath, and in severe cases, it can lead to respiratory failure, pneumonia, and death. The Spanish flu, caused by the H1N1 influenza virus, and the COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 are two of the most significant global health crises in history. While these two pandemics occurred almost a century apart and are caused by different types of viruses, there are notable similarities in their impact, transmission, and public health responses. Here are some key similarities between the Spanish flu and SARS-CoV-2. The Spanish flu pandemic of 1918–1919 stands as one of the deadliest pandemics in human history, claiming the lives of an estimated 50 million people worldwide. Its impact reverberated across continents, leaving behind a legacy of devastation and lessons that, unfortunately, seem to have been forgotten or ignored over time. Despite the advancements in science, medicine, and public health in the intervening century, humanity found itself facing a strikingly similar situation with the outbreak of the COVID-19 pandemic. Additionally, amidst the search for effective measures to combat COVID-19, novel approaches such as iodine complexes, such as Iodine-V has emerged as potential interventions, reflecting the ongoing quest for innovative solutions to mitigate the impact of pandemics. This raises the poignant question: why did we not learn from the Spanish flu?
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The Wells-Riley model is commonly used to assess the probability of viral transmission, taking into account various factors. One of these factors is the ventilation effectiveness, which is commonly assumed to be constant. This article proposes to consider the variability of ventilation efficiency and the inclusion of an additional factor, the dependence of the variability of ventilation efficiency on the variable room heat load and the type of air distribution system in the room, in this established model. The study presents several scenarios simulating probability of airborne transmission of the Omicron variant of the SARS-CoV-2 (causing COVID-19) for typical rooms, such as an office, classroom, and auditorium, for different typical air distribution patterns ('up-up' and 'down-up'), for heat load conditions of two extreme climatic situations: summer (15 August) and winter (31st December), as well as for the maximum and minimum attendance and different types of lighting and room equipment. The study demonstrates that the variability of ventilation effectiveness, depending on the variability of the room's heat load and the air distribution system in the room, influences the probability of pathogen transmission. For an airflow system 'up - up' in classroom, the probability result after 7 h is 15.9 % in winter with minimal heat load (ventilation efficiency from 0.78 to 0.83) and 13.8 % in summer maximum heat load (ventilation efficiency constant and equal to 1.0). to 1.0). For an airflow system 'down - up' in auditorium, the probability result after 4 h is 3.8 % in winter with minimal internal heat gains (ventilation efficiency from 0.82 to 0.92) and 2.8 % in summer maximum internal heat gains (ventilation efficiency from 1.01 to 1.26). This study shows that neglecting this parameter may lead to an underestimation of the transmission risk, thus this article recommends that at least simplifies heat load model should be included in future analyses, and scenarios with different room heat loads should be evaluated separately.
In this paper, the possibility of COVID-19 infection routes analyzed from the viewpoint of fine particle
technology was introduced. Large saliva droplets containing a large amount of virus fall in a short time, and the
contaminated surfaces may cause the source of fomite transmission. However, infection does not occur just by
attaching the virus on our hands. Therefore, hand washing helps prevent infection. In contrast, the amount of
viral load in small droplets that cause aerosol infection is only 0.01-0.001 wt％ of the total viral load in saliva.
Therefore, wearing a mask is very effective in preventing infection. However, depending on contact time and
number of people, accumulation of aerosols in space can cause aerosol infection. Therefore, it is important to
properly ventilate the space. In addition, since highly infectious mutant COVID-19 strains may enhance aerosol
infection, medical knowledge is desired.
To effectively mitigate the risk of respiratory diseases, a significant supply of fresh outdoor air is necessary. However, this requirement results in a considerable increase in energy consumption. This chapter introduces an innovative integrated approach that combines an exhaust air heat pump (EAHP) and advanced air distribution to address this challenge. The findings demonstrate that the integration of the EAHP with advanced air distribution achieves energy savings through three key mechanisms. Firstly, by utilizing the waste heat from the exhaust air, the EAHP decreases the condensation temperature, thus enhancing the coefficient of performance. Secondly, advanced air distribution reduces the ventilation load. Lastly, advanced air distribution lowers the condensation temperature and raises the evaporation temperature, further improving the coefficient of performance. The EAHP alone achieves energy savings of 18%, while advanced air distribution contributes to energy savings of 36%. When combined, the integrated system achieves energy savings of 45%. When compared to a conventional system utilizing an outdoor air heat pump (OAHP) with mixing ventilation, the proposed integrated system of OAHP with stratum ventilation achieves energy savings ranging from 21 to 35% across various outdoor air ratios and temperatures.
Respiratory particles produced during vocalized and nonvocalized activities such as breathing, speaking, and singing serve as a major route for respiratory pathogen transmission. This work reports concomitant measurements of exhaled carbon dioxide volume (VCO2) and minute ventilation (VE), along with exhaled respiratory particles during breathing, exercising, speaking, and singing. Exhaled CO2 and VE measured across healthy adult participants follow a similar trend to particle number concentration during the nonvocalized exercise activities (breathing at rest, vigorous exercise, and very vigorous exercise). Exhaled CO2 is strongly correlated with mean particle number (r = 0.81) and mass (r = 0.84) emission rates for the nonvocalized exercise activities. However, exhaled CO2 is poorly correlated with mean particle number (r = 0.34) and mass (r = 0.12) emission rates during activities requiring vocalization. These results demonstrate that in most real-world environments vocalization loudness is the main factor controlling respiratory particle emission and exhaled CO2 is a poor surrogate measure for estimating particle emission during vocalization. Although measurements of indoor CO2 concentrations provide valuable information about room ventilation, such measurements are poor indicators of respiratory particle concentrations and may significantly underestimate respiratory particle concentrations and disease transmission risk.
After COVID-19, two ventilation approaches have been adopted for infection control. The first is the EN 16798-1 ventilation standard recommended by international organizations. The second is ventilation design, determined according to the risk of infection. This study investigated the effects of various post-COVID-19 ventilation scenarios on the probability of COVID-19 infection, the number of cases, and ventilation rates in four separate university classrooms. Ventilation rates based on infection risk and infection risk were determined by the Wells-Riley mathematical model calibrated to the SARS-CoV-2 virus. The findings showed that the EN 16798-1 ventilation standard may be inadequate in terms of infection risk in classrooms. It showed that ventilation rates determined based on infection risk may not be met by existing HVAC system capacities, even in LEED-certified schools. In possible future pandemics, current ventilation standards and air conditioning system designs in schools should be reviewed in order to control the outbreak.
SARS-CoV-2 is predominantly transmitted through aerosols (i.e., airborne transmission), however, the US Centers for Disease Control and Prevention continue to recommend the use of contact precautions (a gown and gloves) for the care of patients with COVID-19. Infection prevention guidelines should reflect the current science and eliminate this wasteful practice.
Background
There is disagreement about the level of asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We conducted a living systematic review and meta-analysis to address three questions: (1) Amongst people who become infected with SARS-CoV-2, what proportion does not experience symptoms at all during their infection? (2) Amongst people with SARS-CoV-2 infection who are asymptomatic when diagnosed, what proportion will develop symptoms later? (3) What proportion of SARS-CoV-2 transmission is accounted for by people who are either asymptomatic throughout infection or presymptomatic?
Methods and findings
We searched PubMed, Embase, bioRxiv, and medRxiv using a database of SARS-CoV-2 literature that is updated daily, on 25 March 2020, 20 April 2020, and 10 June 2020. Studies of people with SARS-CoV-2 diagnosed by reverse transcriptase PCR (RT-PCR) that documented follow-up and symptom status at the beginning and end of follow-up or modelling studies were included. One reviewer extracted data and a second verified the extraction, with disagreement resolved by discussion or a third reviewer. Risk of bias in empirical studies was assessed with an adapted checklist for case series, and the relevance and credibility of modelling studies were assessed using a published checklist. We included a total of 94 studies. The overall estimate of the proportion of people who become infected with SARS-CoV-2 and remain asymptomatic throughout infection was 20% (95% confidence interval [CI] 17–25) with a prediction interval of 3%–67% in 79 studies that addressed this review question. There was some evidence that biases in the selection of participants influence the estimate. In seven studies of defined populations screened for SARS-CoV-2 and then followed, 31% (95% CI 26%–37%, prediction interval 24%–38%) remained asymptomatic. The proportion of people that is presymptomatic could not be summarised, owing to heterogeneity. The secondary attack rate was lower in contacts of people with asymptomatic infection than those with symptomatic infection (relative risk 0.35, 95% CI 0.10–1.27). Modelling studies fit to data found a higher proportion of all SARS-CoV-2 infections resulting from transmission from presymptomatic individuals than from asymptomatic individuals. Limitations of the review include that most included studies were not designed to estimate the proportion of asymptomatic SARS-CoV-2 infections and were at risk of selection biases; we did not consider the possible impact of false negative RT-PCR results, which would underestimate the proportion of asymptomatic infections; and the database does not include all sources.
Conclusions
The findings of this living systematic review suggest that most people who become infected with SARS-CoV-2 will not remain asymptomatic throughout the course of the infection. The contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand hygiene, masks, testing tracing, and isolation strategies and social distancing, will continue to be needed.
Objectives:
Because detection of SARS-CoV-2 RNA in aerosols but failure to isolate viable (infectious) virus are commonly reported, there is substantial controversy whether SARS-CoV-2 can be transmitted through aerosols. This conundrum occurs because common air samplers can inactivate virions through their harsh collection processes. We sought to resolve the question whether viable SARS-CoV-2 can occur in aerosols using VIVAS air samplers that operate on a gentle water-vapor condensation principle.
Methods:
Air samples collected in the hospital room of two COVID-19 patients, one ready for discharge, the other newly admitted, were subjected to RT-qPCR and virus culture. The genomes of the SARS-CoV-2 collected from the air and isolated in cell culture were sequenced.
Results:
Viable SARS-CoV-2 was isolated from air samples collected 2 to 4.8 m away from the patients. The genome sequence of the SARS-CoV-2 strain isolated from the material collected by the air samplers was identical to that isolated from the newly admitted patient. Estimates of viable viral concentrations ranged from 6 to 74 TCID50 units/L of air.
Conclusions:
Patients with respiratory manifestations of COVID-19 produce aerosols in the absence of aerosol-generating procedures that contain viable SARS-CoV-2, and these aerosols may serve as a source of transmission of the virus.
Importance
There is limited information about the clinical course and viral load in asymptomatic patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Objective
To quantitatively describe SARS-CoV-2 molecular viral shedding in asymptomatic and symptomatic patients.
Design, Setting, and Participants
A retrospective evaluation was conducted for a cohort of 303 symptomatic and asymptomatic patients with SARS-CoV-2 infection between March 6 and March 26, 2020. Participants were isolated in a community treatment center in Cheonan, Republic of Korea.
Main Outcomes and Measures
Epidemiologic, demographic, and laboratory data were collected and analyzed. Attending health care personnel carefully identified patients’ symptoms during isolation. The decision to release an individual from isolation was based on the results of reverse transcription–polymerase chain reaction (RT-PCR) assay from upper respiratory tract specimens (nasopharynx and oropharynx swab) and lower respiratory tract specimens (sputum) for SARS-CoV-2. This testing was performed on days 8, 9, 15, and 16 of isolation. On days 10, 17, 18, and 19, RT-PCR assays from the upper or lower respiratory tract were performed at physician discretion. Cycle threshold (Ct) values in RT-PCR for SARS-CoV-2 detection were determined in both asymptomatic and symptomatic patients.
Results
Of the 303 patients with SARS-CoV-2 infection, the median (interquartile range) age was 25 (22-36) years, and 201 (66.3%) were women. Only 12 (3.9%) patients had comorbidities (10 had hypertension, 1 had cancer, and 1 had asthma). Among the 303 patients with SARS-CoV-2 infection, 193 (63.7%) were symptomatic at the time of isolation. Of the 110 (36.3%) asymptomatic patients, 21 (19.1%) developed symptoms during isolation. The median (interquartile range) interval of time from detection of SARS-CoV-2 to symptom onset in presymptomatic patients was 15 (13-20) days. The proportions of participants with a negative conversion at day 14 and day 21 from diagnosis were 33.7% and 75.2%, respectively, in asymptomatic patients and 29.6% and 69.9%, respectively, in symptomatic patients (including presymptomatic patients). The median (SE) time from diagnosis to the first negative conversion was 17 (1.07) days for asymptomatic patients and 19.5 (0.63) days for symptomatic (including presymptomatic) patients (P = .07). The Ct values for the envelope (env) gene from lower respiratory tract specimens showed that viral loads in asymptomatic patients from diagnosis to discharge tended to decrease more slowly in the time interaction trend than those in symptomatic (including presymptomatic) patients (β = −0.065 [SE, 0.023]; P = .005).
Conclusions and Relevance
In this cohort study of symptomatic and asymptomatic patients with SARS-CoV-2 infection who were isolated in a community treatment center in Cheonan, Republic of Korea, the Ct values in asymptomatic patients were similar to those in symptomatic patients. Isolation of asymptomatic patients may be necessary to control the spread of SARS-CoV-2.
Background - There currently is substantial controversy about the role played by SARS-CoV-2 in aerosols in disease transmission, due in part to detections of viral RNA but failures to isolate viable virus from clinically generated aerosols.
Methods - Air samples were collected in the room of two COVID-19 patients, one of whom had an active respiratory infection with a nasopharyngeal (NP) swab positive for SARS-CoV-2 by RT-qPCR. By using VIVAS air samplers that operate on a gentle water-vapor condensation principle, material was collected from room air and subjected to RT-qPCR and virus culture. The genomes of the SARS-CoV-2 collected from the air and of virus isolated in cell culture from air sampling and from a NP swab from a newly admitted patient in the room were sequenced.
Findings - Viable virus was isolated from air samples collected 2 to 4.8m away from the patients. The genome sequence of the SARS-CoV-2 strain isolated from the material collected by the air samplers was identical to that isolated from the NP swab from the patient with an active infection. Estimates of viable viral concentrations ranged from 6 to 74 TCID50 units/L of air.
Interpretation - Patients with respiratory manifestations of COVID-19 produce aerosols in the absence of aerosol-generating procedures that contain viable SARS-CoV-2, and these aerosols may serve as a source of transmission of the virus.
Background
There has been little focus on the individual risk of acquiring COVID-19 related to choir practice.
Methods
We report the case of a high transmission rate of SARS-CoV-2 linked to an indoor choir rehearsal in France in March 2020 at the beginning of the COVID-19 pandemic.
Results
A total of 27 participants, including 25 male singers, a conductor and an accompanist attended a choir practice on March 12, 2020. The practice was indoor and took place in a non-ventilated space of 45 m ² . No choir member reported having been symptomatic for COVID-19 between March 2 and March 12.The mean age of the participants was 66.9 (range 35-86) years. 70% of the participants (19 of 27) were diagnosed with COVID-19 from 1 to 12 days after the rehearsal with a median of 5.1 days. 36% of the cases needed a hospitalization (7/19), and 21% (4/19) were admitted to an ICU. The index cases were possibly multiple.
Discussion
The choir practice was planned in March 2020 at a period when the number of new cases of COVID-19 began to grow exponentially in France because SARS-CoV-2 was actively circulating. The secondary attack rate (70%) was much higher than it is described within households (10-20%) and among close contacts made outside households (0-5%). Singing might have contributed to enhance SARS-CoV-2 person-to-person transmission through emission of droplets and aerosolization in a closed non ventilated space with a relative high number of people including multiple pre-symptomatic suspected index cases.
Conclusion
Indoor choir practice should be suspended during SARS-CoV-2 outbreaks. Further studies are necessary to test the spread of the virus by the act of singing. As the benefits of the barrier measures and social distancing are known to be effective in terms of a reduction in the incidence of the COVID-19, experts’ recommendations concerning the resuming of choir practice are necessary.
We analyzed 3,184 cases of coronavirus disease in Japan and identified 61 case-clusters in healthcare and other care facilities, restaurants and bars, workplaces, and music events. We also identified 22 probable primary case-patients for the clusters; most were 20-39 years of age and presymptomatic or asymptomatic at virus transmission.
As children are under-represented in current studies aiming to analyse transmission of SARS-coronavirus 2 (SARS-CoV-2), their contribution to transmission is unclear. Viral load, as measured by RT-PCR, can inform considerations regarding transmission, especially if existing knowledge of viral load in other respiratory diseases is taken into account. RT-PCR threshold cycle data from 3303 patients who tested positive for SARS-CoV-2 (out of 77,996 persons tested in total, drawn from across Germany) were analysed to examine the relationship between patient age and estimated viral load. Two PCR systems were used. In data from the PCR system predominantly used for community and cluster screening during the early phase of the epidemic (Roche LightCycler 480 II), when such screening was frequent practice, viral loads do not differ significantly in three comparisons between young and old age groups (differences in log10 viral loads between young and old estimated from raw viral load data and a Bayesian mixture model of gamma distributions collectively range between -0.11 and -0.43). Data from a second type of PCR system (Roche cobas 6800/8800), introduced into diagnostic testing on March 16, 2020 and used during the time when household and other contact testing was reduced, show a credible but small difference in the three comparisons between young and old age groups (differences, measured as above, collectively range between -0.43 and -0.83). This small difference may be due to differential patterns of PCR instrument utilization rather than to an actual difference in viral load. Considering household transmission data on influenza, which has a similar viral load kinetic to SARS-CoV-2, the viral load differences between age groups observed in this study are likely to be of limited relevance. Combined data from both PCR instruments show that viral loads of at least 250,000 copies, a threshold we previously established for the isolation of infectious virus in cell culture at more than 5% probability, were present across the study period in 29.0% of kindergarten-aged patients 0-6 years old (n=38), 37.3% of those aged 0-19 (n=150), and in 51.4% of those aged 20 and above (n=3153). The differences in these fractions may also be due to differences in test utilization. We conclude that a considerable percentage of infected people in all age groups, including those who are pre- or mild-symptomatic, carry viral loads likely to represent infectivity. Based on these results and uncertainty about the remaining incidence, we recommend caution and careful monitoring during gradual lifting of non-pharmaceutical interventions. In particular, there is little evidence from the present study to support suggestions that children may not be as infectious as adults.
Despite notable efforts in airborne SARS-CoV-2 detection, no clear evidence has emerged to show how SARS-CoV-2 is emitted into the environments. Here, 35 COVID-19 subjects were recruited; exhaled breath condensate (EBC), air samples and surface swabs were collected and analyzed for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR). EBC samples had the highest positive rate (16.7%, n = 30), followed by surface swabs(5.4%, n = 242), and air samples (3.8%, n = 26). COVID-19 patients were shown to exhale SARSCoV-2 into the air at an estimated rate of 10 ³ -10 ⁵ RNA copies/min; while toilet and floor surfaces represented two important SARS-CoV-2 reservoirs. Our results imply that airborne transmission of SARS-CoV-2 plays a major role in COVID-19 spread, especially during the early stages of the disease.
One Sentence Summary
COVID-19 patient exhales millions of SARS-CoV-2 particles per hour
Understanding the particle size distribution in the air and patterns of environmental contamination of SARS-CoV-2 is essential for infection prevention policies. Here we screen surface and air samples from hospital rooms of COVID-19 patients for SARS-CoV-2 RNA. Environmental sampling is conducted in three airborne infection isolation rooms (AIIRs) in the ICU and 27 AIIRs in the general ward. 245 surface samples are collected. 56.7% of rooms have at least one environmental surface contaminated. High touch surface contamination is shown in ten (66.7%) out of 15 patients in the first week of illness, and three (20%) beyond the first week of illness (p = 0.01, χ2 test). Air sampling is performed in three of the 27 AIIRs in the general ward, and detects SARS-CoV-2 PCR-positive particles of sizes >4 µm and 1–4 µm in two rooms, despite these rooms having 12 air changes per hour. This warrants further study of the airborne transmission potential of SARS-CoV-2. Here, the authors sample air and surfaces in hospital rooms of COVID-19 patients, detect SARS-CoV-2 RNA in air samples of two of three tested airborne infection isolation rooms, and find surface contamination in 66.7% of tested rooms during the first week of illness and 20% beyond the first week of illness.
During the rapid rise in COVID-19 illnesses and deaths globally, and notwithstanding recommended precautions, questions are voiced about routes of transmission for this pandemic disease. Inhaling small airborne droplets is probable as a third route of infection, in addition to more widely recognized transmission via larger respiratory droplets and direct contact with infected people or contaminated surfaces. While uncertainties remain regarding the relative contributions of the different transmission pathways, we argue that existing evidence is sufficiently strong to warrant engineering controls targeting airborne transmission as part of an overall strategy to limit infection risk indoors. Appropriate building engineering controls include sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, avoiding air recirculation and avoiding overcrowding. Often, such measures can be easily implemented and without much cost, but if only they are recognised as significant in contributing to infection control goals. We believe that the use of engineering controls in public buildings, including hospitals, shops, offices, schools, kindergartens, libraries, restaurants, cruise ships, elevators, conference rooms or public transport, in parallel with effective application of other controls (including isolation and quarantine, social distancing and hand hygiene), would be an additional important measure globally to reduce the likelihood of transmission and thereby protect healthcare workers, patients and the general public.
Airborne transmission is a pathway of contagion that is still not sufficiently investigated despite the evidence in the scientific literature of the role it can play in the context of an epidemic. While the medical research area dedicates efforts to find cures and remedies to counteract the effects of a virus, the engineering area is involved in providing risk assessments in indoor environments by simulating the airborne transmission of the virus during an epidemic. To this end, virus air emission data are needed. Unfortunately, this information is usually available only after the outbreak, based on specific reverse engineering cases. In this work, a novel approach to estimate the viral load emitted by a contagious subject on the basis of the viral load in the mouth, the type of respiratory activity (e.g. breathing, speaking, whispering), respiratory physiological parameters (e.g. inhalation rate), and activity level (e.g. resting, standing, light exercise) is proposed.
The results showed that high quanta emission rates (>100 quanta h⁻¹) can be reached by an asymptomatic infectious SARS-CoV-2 subject performing vocalization during light activities (i.e. walking slowly) whereas a symptomatic SARS-CoV-2 subject in resting conditions mostly has a low quanta emission rate (<1 quantum h⁻¹).
The findings in terms of quanta emission rates were then adopted in infection risk models to demonstrate its application by evaluating the number of people infected by an asymptomatic SARS-CoV-2 subject in Italian indoor microenvironments before and after the introduction of virus containment measures. The results obtained from the simulations clearly highlight that a key role is played by proper ventilation in containment of the virus in indoor environments.
Background
So far, one of the major drawbacks of the available molecular assays for the diagnosis of severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) is the need for viral nucleic acid extractionfrom clinical specimens.
Objective
The aim of this study was to evaluate the performances of a newly designed real-time RT-PCR (Simplexa™ COVID-19 Direct assay), that is established with an all-in-one reagent mix and no separate extraction required.
Results
The lower limit of detection (LOD) for both target genes resulted the same: 3.2 (CI: 2.9 to 3.8) log10 cp/mL and 0.40 (CI: 0.2 to 1.5) TCID50/mL for S gene while 3.2 log10 (CI: 2.9 to 3.7) log10 cp/mL and 0.4 (CI: 0.2 to 1.3) TCID50/mL for ORF1ab. The LOD obtained with extracted viral RNA for both S gene or ORF1ab was 2.7 log10 cp/mL. Crossreactive analysis performed in 20 nasopharyngeal swabs confirmed a 100% of clinical specificity of the assay. Clinical performances of Simplexa™ COVID-19 Direct assay were assessed in 278 nasopharyngeal swabs tested in parallel with Corman's method. Concordance analysis showed an "almost perfect" agreement in SARS-CoV-2 RNA detection between the two assays, being κ = 0.938; SE = 0.021; 95% CI = 0.896-0.980.
Conclusions
The high sensitivity and specificity of this new assay indicate that it is promising for laboratory diagnosis, enabling highspeed detection in just over one hour, which is significantly faster than the up to five hours currently required by traditional extraction followed by amplification technologies, thus allowing prompt decision making regarding isolation of infected patients.
The ongoing COVID-19 outbreak has spread rapidly on a global scale. While the transmission of SARS-CoV-2 via human respiratory droplets and direct contact is clear, the potential for aerosol transmission is poorly understood1–3. This study investigated the aerodynamic nature of SARS-CoV-2 by measuring viral RNA in aerosols in different areas of two Wuhan hospitals during the COVID-19 outbreak in February and March 2020. The concentration of SARS-CoV-2 RNA in aerosols detected in isolation wards and ventilated patient rooms was very low, but it was elevated in the patients’ toilet areas. Levels of airborne SARS-CoV-2 RNA in the majority of public areas was undetectable except in two areas prone to crowding, possibly due to infected carriers in the crowd. We found that some medical staff areas initially had high concentrations of viral RNA with aerosol size distributions showing peaks in submicrometre and/or supermicrometre regions, but these levels were reduced to undetectable levels after implementation of rigorous sanitization procedures. Although we have not established the infectivity of the virus detected in these hospital areas, we propose that SARS-CoV-2 may have the potential to be transmitted via aerosols. Our results indicate that room ventilation, open space, sanitization of protective apparel, and proper use and disinfection of toilet areas can effectively limit the concentration of SARS-CoV-2 RNA in aerosols. Future work should explore the infectivity of aerosolized virus.
We report temporal patterns of viral shedding in 94 patients with laboratory-confirmed COVID-19 and modeled COVID-19 infectiousness profiles from a separate sample of 77 infector–infectee transmission pairs. We observed the highest viral load in throat swabs at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset. We estimated that 44% (95% confidence interval, 25–69%) of secondary cases were infected during the index cases’ presymptomatic stage, in settings with substantial household clustering, active case finding and quarantine outside the home. Disease control measures should be adjusted to account for probable substantial presymptomatic transmission. Presymptomatic transmission of SARS-CoV-2 is estimated to account for a substantial proportion of COVID-19 cases.
To determine distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards in Wuhan, China, we tested air and surface samples. Contamination was greater in intensive care units than general wards. Virus was widely distributed on floors, computer mice, trash cans, and sickbed handrails and was detected in air ≈4 m from patients.
Coronavirus disease 2019 (COVID-19) is an acute respiratory tract infection that emerged in late 20191,2. Initial outbreaks in China involved 13.8% cases with severe, and 6.1% with critical courses³. This severe presentation corresponds to the usage of a virus receptor that is expressed predominantly in the lung2,4. By causing an early onset of severe symptoms, this same receptor tropism is thought to have determined pathogenicity, but also aided the control, of severe acute respiratory syndrome (SARS) in 2003⁵. However, there are reports of COVID-19 cases with mild upper respiratory tract symptoms, suggesting the potential for pre- or oligosymptomatic transmission6–8. There is an urgent need for information on body site-specific virus replication, immunity, and infectivity. Here we provide a detailed virological analysis of nine cases, providing proof of active virus replication in upper respiratory tract tissues. Pharyngeal virus shedding was very high during the first week of symptoms (peak at 7.11 × 10⁸ RNA copies per throat swab, day 4). Infectious virus was readily isolated from throat- and lung-derived samples, but not from stool samples, in spite of high virus RNA concentration. Blood and urine never yielded virus. Active replication in the throat was confirmed by viral replicative RNA intermediates in throat samples. Sequence-distinct virus populations were consistently detected in throat and lung samples from the same patient, proving independent replication. Shedding of viral RNA from sputum outlasted the end of symptoms. Seroconversion occurred after 7 days in 50% of patients (14 days in all), but was not followed by a rapid decline in viral load. COVID-19 can present as a mild upper respiratory tract illness. Active virus replication in the upper respiratory tract puts the prospects of COVID-19 containment in perspective.
Lack of evidence on SARS-CoV-2 transmission dynamics has led to shifting isolation guidelines between airborne and droplet isolation precautions. During the initial isolation of 13 individuals confirmed positive with COVID-19 infection, air and surface samples were collected in eleven isolation rooms to examine viral shedding from isolated individuals. While all individuals were confirmed positive for SARS-CoV-2, symptoms and viral shedding to the environment varied considerably. Many commonly used items, toilet facilities, and air samples had evidence of viral contamination, indicating that SARS-CoV-2 is shed to the environment as expired particles, during toileting, and through contact with fomites. Disease spread through both direct (droplet and person-to-person) as well as indirect contact (contaminated objects and airborne transmission) are indicated, supporting the use of airborne isolation precautions.
One Sentence Summary
SARS-CoV-2 is shed during respiration, toileting, and fomite contact, indicating that infection may occur in both direct and indirect contact.
It appears inevitable that severe acute respiratory syndrome coronavirus 2 will continue to spread. Although we still have limited information on the epidemiology of this virus, there have been multiple reports of superspreading events (SSEs), which are associated with both explosive growth early in an outbreak and sustained transmission in later stages. Although SSEs appear to be difficult to predict and therefore difficult to prevent, core public health actions can prevent and reduce the number and impact of SSEs. To prevent and control of SSEs, speed is essential. Prevention and mitigation of SSEs depends, first and foremost, on quickly recognizing and understanding these events, particularly within healthcare settings. Better understanding transmission dynamics associated with SSEs, identifying and mitigating high-risk settings, strict adherence to healthcare infection prevention and control measures, and timely implementation of nonpharmaceutical interventions can help prevent and control severe acute respiratory syndrome coronavirus 2, as well as future infectious disease outbreaks.
Background: The outbreak of coronavirus disease 2019 (COVID-19) and SARS-CoV-2 have placed unprecedented challenges on hospital environmental hygiene and medical staffs protection. It is crucial to assess hospital environmental hygiene to understand the most important environmental issues for controlling the spread of 2019-nCoV in hospitals.
Objective: To detect the presence of the COVID-19 in the air and on the surfaces of the guide station, fever clinic, and isolation areas, and the close contacts medical staffs in the First Hospital of Jilin University.
Methods: Viruses in the air were collected by natural sedimentation and air particle sampler methods. Predetermined environmental surfaces were sampled using swabs at seven o'clock in the morning before disinfection. The samples from close contacts medical staffs were throat swab samples. Quantitative real-time PCR methods were used to confirm the existence of COVID-19 pathogens.
Results: Viruses could be detected on the surfaces of the nurse station in the isolation area with suspected patients and in the air of the isolation ward with an intensive care patient.
Conclusion: Comprehensive monitoring of hospital environmental hygiene during pandemic outbreaks is conducive to the refinement of hospital infection control. It is of great significance to ensure the safety of medical treatment and the quality of hospital infection control through the monitoring of environmental hygiene.
A novel coronavirus (2019-nCoV) is causing an outbreak of viral pneumonia that started in Wuhan, China. Using the travel history and symptom onset of 88 confirmed cases that were detected outside Wuhan in the early outbreak phase, we estimate the mean incubation period to be 6.4 days (95% credible interval: 5.6 7.7), ranging from 2.1 to 11.1 days (2.5th to 97.5th percentile). These values should help inform 2019-nCoV case definitions and appropriate quarantine durations. © 2020 European Centre for Disease Prevention and Control (ECDC). All rights reserved.
Background:
The initial cases of novel coronavirus (2019-nCoV)-infected pneumonia (NCIP) occurred in Wuhan, Hubei Province, China, in December 2019 and January 2020. We analyzed data on the first 425 confirmed cases in Wuhan to determine the epidemiologic characteristics of NCIP.
Methods:
We collected information on demographic characteristics, exposure history, and illness timelines of laboratory-confirmed cases of NCIP that had been reported by January 22, 2020. We described characteristics of the cases and estimated the key epidemiologic time-delay distributions. In the early period of exponential growth, we estimated the epidemic doubling time and the basic reproductive number.
Results:
Among the first 425 patients with confirmed NCIP, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period was 5.2 days (95% confidence interval [CI], 4.1 to 7.0), with the 95th percentile of the distribution at 12.5 days. In its early stages, the epidemic doubled in size every 7.4 days. With a mean serial interval of 7.5 days (95% CI, 5.3 to 19), the basic reproductive number was estimated to be 2.2 (95% CI, 1.4 to 3.9).
Conclusions:
On the basis of this information, there is evidence that human-to-human transmission has occurred among close contacts since the middle of December 2019. Considerable efforts to reduce transmission will be required to control outbreaks if similar dynamics apply elsewhere. Measures to prevent or reduce transmission should be implemented in populations at risk. (Funded by the Ministry of Science and Technology of China and others.).
Mechanistic hypotheses about airborne infectious disease transmission have traditionally emphasized the role of coughing and sneezing, which are dramatic expiratory events that yield both easily visible droplets and large quantities of particles too small to see by eye. Nonetheless, it has long been known that normal speech also yields large quantities of particles that are too small to see by eye, but are large enough to carry a variety of communicable respiratory pathogens. Here we show that the rate of particle emission during normal human speech is positively correlated with the loudness (amplitude) of vocalization, ranging from approximately 1 to 50 particles per second (0.06 to 3 particles per cm3) for low to high amplitudes, regardless of the language spoken (English, Spanish, Mandarin, or Arabic). Furthermore, a small fraction of individuals behaves as “speech superemitters,” consistently releasing an order of magnitude more particles than their peers. Our data demonstrate that the phenomenon of speech superemission cannot be fully explained either by the phonic structures or the amplitude of the speech. These results suggest that other unknown physiological factors, varying dramatically among individuals, could affect the probability of respiratory infectious disease transmission, and also help explain the existence of superspreaders who are disproportionately responsible for outbreaks of airborne infectious disease.
Significance
Lack of human data on influenza virus aerosol shedding fuels debate over the importance of airborne transmission. We provide overwhelming evidence that humans generate infectious aerosols and quantitative data to improve mathematical models of transmission and public health interventions. We show that sneezing is rare and not important for—and that coughing is not required for—influenza virus aerosolization. Our findings, that upper and lower airway infection are independent and that fine-particle exhaled aerosols reflect infection in the lung, opened a pathway for a deeper understanding of the human biology of influenza infection and transmission. Our observation of an association between repeated vaccination and increased viral aerosol generation demonstrated the power of our method, but needs confirmation.
Background:
In order to prepare for a possible influenza pandemic, a better understanding of the potential for airborne transmission of influenza from person to person is needed.
Objectives:
The objective of this study was to directly compare the generation of aerosol particles containing viable influenza virus during coughs and exhalations.
Methods:
Sixty-one adult volunteer outpatients with influenza-like symptoms were asked to cough and exhale three times into a spirometer. Aerosol particles produced during coughing and exhalation were collected into liquid media using aerosol samplers. The samples were tested for the presence of viable influenza virus using a viral replication assay (VRA).
Results:
Fifty-three test subjects tested positive for influenza A virus. Of these, 28 (53%) produced aerosol particles containing viable influenza A virus during coughing, and 22 (42%) produced aerosols with viable virus during exhalation. Thirteen subjects had both cough aerosol and exhalation aerosol samples that contained viable virus, 15 had positive cough aerosol samples but negative exhalation samples, and 9 had positive exhalation samples but negative cough samples.
Conclusions:
Viable influenza A virus was detected more often in cough aerosol particles than in exhalation aerosol particles, but the difference was not large. Since individuals breathe much more often than they cough, these results suggest that breathing may generate more airborne infectious material than coughing over time. However, both respiratory activities could be important in airborne influenza transmission. Our results are also consistent with the theory that much of the aerosol containing viable influenza originates deep in the lungs. This article is protected by copyright. All rights reserved.
We present two real-time reverse-transcription polymerase chain reaction assays for a novel human coronavirus (CoV), targeting regions upstream of the E gene (upE) or within open reading frame (ORF)1b, respectively. Sensitivity for upE is 3.4 copies per reaction (95% confidence interval (CI): 2.5–6.9 copies) or 291 copies/mL of sample. No cross-reactivity was observed with coronaviruses OC43, NL63, 229E, SARS-CoV, nor with 92 clinical specimens containing common human respiratory viruses. We recommend using upE for screening and ORF1b for confirmation
Travel in passenger cars is a ubiquitous aspect of the daily activities of many people. During the 2009 influenza A(H1N1) pandemic a case of probable transmission during car travel was reported in Australia, to which spread via the airborne route may have contributed. However, there are no data to indicate the likely risks of such events, and how they may vary and be mitigated. To address this knowledge gap, we estimated the risk of airborne influenza transmission in two cars (1989 model and 2005 model) by employing ventilation measurements and a variation of the Wells-Riley model. Results suggested that infection risk can be reduced by not recirculating air; however, estimated risk ranged from 59% to 99·9% for a 90-min trip when air was recirculated in the newer vehicle. These results have implications for interrupting in-car transmission of other illnesses spread by the airborne route.
There is mounting evidence that the aerosol transmission route plays a significant role in the spread of influenza in temperate regions and that the efficiency of this route depends on humidity. Nevertheless, the precise mechanisms by which humidity might influence transmissibility via the aerosol route have not been elucidated. We hypothesize that airborne concentrations of infectious influenza A viruses (IAVs) vary with humidity through its influence on virus inactivation rate and respiratory droplet size. To gain insight into the mechanisms by which humidity might influence aerosol transmission, we modeled the size distribution and dynamics of IAVs emitted from a cough in typical residential and public settings over a relative humidity (RH) range of 10-90%. The model incorporates the size transformation of virus-containing droplets due to evaporation and then removal by gravitational settling, ventilation, and virus inactivation. The predicted concentration of infectious IAVs in air is 2.4 times higher at 10% RH than at 90% RH after 10 min in a residential setting, and this ratio grows over time. Settling is important for removal of large droplets containing large amounts of IAVs, while ventilation and inactivation are relatively more important for removal of IAVs associated with droplets <5 µm. The inactivation rate increases linearly with RH; at the highest RH, inactivation can remove up to 28% of IAVs in 10 min. Humidity is an important variable in aerosol transmission of IAVs because it both induces droplet size transformation and affects IAV inactivation rates. Our model advances a mechanistic understanding of the aerosol transmission route, and results complement recent studies on the relationship between humidity and influenza's seasonality. Maintaining a high indoor RH and ventilation rate may help reduce chances of IAV infection.
Objective
to document the case of a high transmission rate of SARS-CoV-2 generating a cluster linked to an indoor choir rehearsal hold at the beginning of the COVID-19 pandemic in France.
Method
case study. Data were obtained via a questionnaire.
Results
27 participants, including 25 singers, one conductor and one accompanist attended a choir practice on March 12, 2020. The practice was indoor and took place in a non-ventilated space of 45 m 2 . No choir member reported having been symptomatic for COVID-19 between March 2 and March 12.The mean age of the participants was 66.9 (range 35-86) years. The secondary attack rate was 70%: 19/27 participants were diagnosed with COVID-19 from 1 to 12 days after the rehearsal with a median of 5.1 days. 36% of the cases needed a hospitalization (7/19), and 21% (4/19) were admitted to an ICU. The index cases were asymptomatic and possibly multiple.
Conclusion
in the absence of valid barrier measures to prevent COVID-19 transmission, indoor choir practice should be suspended during the SARSCoV-2 surging phases. Transmission of the virus among gatherings from asymptomatic cases is a crucial issue and a main challenge to COVID-19 control.
It is essential to understand where and howsevere acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2)is transmitted.Case reports were extracted from the local Municipal Health Commissions of 320prefecturalmunicipalities in China (not including Hubei province). We identified alloutbreaks involving three or more cases and reviewed the major characteristics of the enclosed spaces in which the outbreakswere reported and their associated indoor environmental aspects.Three hundred and eighteen outbreaks with three or more cases were identified,comprising a total of 1245 confirmed cases in 120prefectural cities. Amongst the identified outbreaks, 53.8% involved three cases, 26.4%involved four cases, and only 1.6%involved ten or more cases. Home‐based outbreakswere the dominant category (254 of 318 outbreaks;79.9%), followed by transport‐based outbreaks (108;34.0%), and many outbreaks occurred in more than one categoryof venue. All identified outbreaksof three or more cases occurred in indoor environments, which confirmsthat sharing indoor spaceswith one or more infected persons isa major SARS‐CoV‐2 infection risk.
On March 17, 2020, a member of a Skagit County, Washington, choir informed Skagit County Public Health (SCPH) that several members of the 122-member choir had become ill. Three persons, two from Skagit County and one from another area, had test results positive for SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). Another 25 persons had compatible symptoms. SCPH obtained the choir's member list and began an investigation on March 18. Among 61 persons who attended a March 10 choir practice at which one person was known to be symptomatic, 53 cases were identified, including 33 confirmed and 20 probable cases (secondary attack rates of 53.3% among confirmed cases and 86.7% among all cases). Three of the 53 persons who became ill were hospitalized (5.7%), and two died (3.7%). The 2.5-hour singing practice provided several opportunities for droplet and fomite transmission, including members sitting close to one another, sharing snacks, and stacking chairs at the end of the practice. The act of singing, itself, might have contributed to transmission through emission of aerosols, which is affected by loudness of vocalization (1). Certain persons, known as superemitters, who release more aerosol particles during speech than do their peers, might have contributed to this and previously reported COVID-19 superspreading events (2-5). These data demonstrate the high transmissibility of SARS-CoV-2 and the possibility of superemitters contributing to broad transmission in certain unique activities and circumstances. It is recommended that persons avoid face-to-face contact with others, not gather in groups, avoid crowded places, maintain physical distancing of at least 6 feet to reduce transmission, and wear cloth face coverings in public settings where other social distancing measures are difficult to maintain.
Background
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can spread rapidly within skilled nursing facilities. After identification of a case of Covid-19 in a skilled nursing facility, we assessed transmission and evaluated the adequacy of symptom-based screening to identify infections in residents.
Methods
We conducted two serial point-prevalence surveys, 1 week apart, in which assenting residents of the facility underwent nasopharyngeal and oropharyngeal testing for SARS-CoV-2, including real-time reverse-transcriptase polymerase chain reaction (rRT-PCR), viral culture, and sequencing. Symptoms that had been present during the preceding 14 days were recorded. Asymptomatic residents who tested positive were reassessed 7 days later. Residents with SARS-CoV-2 infection were categorized as symptomatic with typical symptoms (fever, cough, or shortness of breath), symptomatic with only atypical symptoms, presymptomatic, or asymptomatic.
Results
Twenty-three days after the first positive test result in a resident at this skilled nursing facility, 57 of 89 residents (64%) tested positive for SARS-CoV-2. Among 76 residents who participated in point-prevalence surveys, 48 (63%) tested positive. Of these 48 residents, 27 (56%) were asymptomatic at the time of testing; 24 subsequently developed symptoms (median time to onset, 4 days). Samples from these 24 presymptomatic residents had a median rRT-PCR cycle threshold value of 23.1, and viable virus was recovered from 17 residents. As of April 3, of the 57 residents with SARS-CoV-2 infection, 11 had been hospitalized (3 in the intensive care unit) and 15 had died (mortality, 26%). Of the 34 residents whose specimens were sequenced, 27 (79%) had sequences that fit into two clusters with a difference of one nucleotide.
Conclusions
Rapid and widespread transmission of SARS-CoV-2 was demonstrated in this skilled nursing facility. More than half of residents with positive test results were asymptomatic at the time of testing and most likely contributed to transmission. Infection-