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It is Time to Address Airborne Transmission of COVID-19
... Bei der Übertragung von SARS-CoV-2 von Mensch zu Mensch scheinen Viruskontaminierte Luftschwebeteilchen (Aerosole) eine entscheidende Rolle bei der Infektion zu spielen [9,11,28,31,37]. In Abhängigkeit vom "Ausstoß" (Sprechen, Atmen, Singen, Husten, Niesen . . . ) werden Partikel verschiedener Größe produziert und in die Raumluft abgegeben. ...
... SARS-CoV-2 · Coronavirus · Pandemic · Infection · Room air filter kel oder das Virus selbst können mehrere Stunden in der Raumluft nachgewiesen werden [23,27,28,36]. Besondere Bedeutung kommt vor diesem Hintergrund Aerosolen von einer Größe von < 5 μm zu, da diese kleinen und kleinsten Teilchen bereits beim normalen Atmen und Sprechen entstehen und tief in den Respirationstrakt bis auf Ebene der Alveolen vordringen können [2,23,26,36]. ...
... Insgesamt halten wir in Übereinstimmung mit anderen Autoren die Verwendung von Raumluftfiltern für empfehlenswert [5,7,21,[28][29][30]33] ...
Zusammenfassung
Hintergrund
Vor dem Hintergrund der Corona-Pandemie wurde mit Beginn des Sommersemesters 2020 bundesweit die studentische Präsenzlehre praktisch eingestellt. Ebenso wurden im Rahmen des zweiten Lockdowns in vielen Bundesländern Schulen und Kindertagesstätten geschlossen bzw. auf ein Minimum heruntergefahren. In diesem Zusammenhang wurde bereits mehrfach der Effekt von Raumluftfiltern diskutiert, nach Ansicht des Umweltbundesamtes ist der Einsatz von mobilen Luftreinigern derzeit allerdings nicht empfohlen. Die vorliegende Untersuchung zeigt die konkreten Auswirkungen von mobilen Raumluftfiltern auf die Aerosolbelastung in einem Hörsaal, einer Kantine und einem schulischen Lernzentrum auf.
Methoden
In 3 Großräumen (studentischer Hörsaal, Betriebskantine, Lernzentrum eines Gymnasiums) wurde der Effekt von mobilen Raumluftfiltern (Fa. DEMA-airtech, Stuttgart) gemessen. Die Messungen der Aerosolkonzentrationen bzw. der CO 2 -Werte erfolgte mit Geräten der Firma Palas, Karlsruhe.
Ergebnisse
In allen 3 Szenarien zeigte sich übereinstimmend, dass die Aerosolkonzentration durch die Filter relevant und dauerhaft reduziert werden konnten. Der Effekt erschien teilweise sogar nachhaltiger und effektiver als beim normalen Stoßlüften.
Schlussfolgerung
Die Verwendung von Raumluftfiltern als ergänzende Maßnahme zum Abstandhalten und dem Tragen einer effektiven Mund-Nase-Bedeckung ist eine empfehlenswerte Maßnahme, die die Wiederaufnahme der Präsenzlehre ermöglichen könnte.
... One year into the pandemic, there is still some controversy about how the virus uses the airborne route for person-to-person transmission. It has been known since the late nineteenth century that respiratory diseases are transmitted by direct or indirect contact with infectious material, respiratory droplets (Flügge droplets larger than 5 microns) or aerosols [5,6]. The larger respiratory droplets can spread up to a maximum of about 2 m from the source [5]. ...
... The trajectory of this cloud depends on the ambient humidity, temperature, velocity and force of expulsion. These aerosols are currently being held responsible for high pollution rates, mainly in enclosed or poorly ventilated places [5][6][7]. ...
... By knowing the routes of transmission, appropriate preventive measures designed to minimise transmission of infection can be adopted, bearing in mind that to date, results point to a possible risk of aerosol transmission of SARS-CoV-2 [5,6]. ...
Background
This study evaluates the particle dispersion involved in dental procedures carried out during orthodontic treatments. Variants such as temperature and relative humidity in the dental cabinet were considered.
Methods
Using a particle counter, a pilot study was conducted, in which 98 consecutive recordings were made during appointments of patients undergoing orthodontic treatments. Temperature, relative humidity and particles present at the beginning (AR) and during the appointment (BR) were recorded. A control record (CR) of temperature, relative humidity and particles present was made before the start of the clinical activity. In addition to conventional statistics, differential descriptive procedures were used to analyse results, and the influence of relative humidity on particle concentration was analysed by statistical modelling with regression equations.
Results
The number of particles present, regardless of their size, was much higher in AR than in CR (p < .001). The same was true for relative humidity and ambient temperature. The relationship between relative humidity and particle number was determined to be exponential.
Limitations of the study
The limitations are associated with sample size, environmental conditions of the room and lack of discrimination among the procedures performed.
Conclusions
This pilot study shows that from the moment a patient enters a dental office, a large number of additional particles are generated. During treatment, the number of particles of 0.3 microns—which have a high capacity to penetrate the respiratory tract-increases. Moreover, a relationship between relative humidity and particle formation is observed. Further studies are needed.
... With the recognition that COVID-19 and other diseases may be primarily transmitted through respiratory aerosols (Greenhalgh et al., 2021;Morawska and Milton, 2020;Bazant and Bush, 2021), it is crucial to understand how buildings and HVAC systems can influence the risk of indoor airborne transmission (Morawska et al., 2021). While it is tempting from a practical standpoint to impose one-size-fits-all limits on occupancy or social distance, the unfortunate reality is that indoor air conditions vary significantly with climate, building type, and use. ...
... In indoor environments, these particles are spread throughout a space due to natural air currents and recirculation provided by the HVAC system (Bhagat et al., 2020;Linden, 1999;Foster and Kinzel, 2021), thus providing a potential route for disease transmission to susceptible individuals in the space who inhale them and are exposed to the pathogens they contain. Although not all diseases can be spread in this way, the airborne transmission pathway has been identified for many especially contagious respiratory diseases (tuberculosis, measles, influenza, SARS-CoV), and it has increasingly been recognized as the primary transmission route for SARS-CoV-2, the virus responsible for the COVID-19 pandemic (Bazant and Bush, 2021;Greenhalgh et al., 2021;Morawska and Milton, 2020). ...
It has been established that combinations of increased ventilation, improved filtration, and other HVAC techniques can reduce the likelihood of airborne disease transmission in buildings. However, with only qualitative guidance, it is difficult for building managers to make informed decisions. Furthermore, the possible actions almost always require additional energy consumption, which is generally not well characterized. To address this knowledge gap, we propose simplified physics-based models that can be used to quantify both the expected transmission rate and the associated energy consumption that result from HVAC system operation. By formulating all disinfection mechanisms in terms of "equivalent outdoor air", a common basis is established for comparing and combining different strategies. The transmission rate can thus be modeled by considering the airborne concentration of infectious particles that would result from an infector in the space. Energy consumption is then estimated by considering the change in HVAC variables and applying standard analysis. To illustrate the insights provided by these models, we present examples of how the proposed analysis can be applied to specific spaces, highlighting the fact that underlying transmission risk and energy-optimal disinfection strategies can vary significantly based on space characteristics.
... Airborne infections originate from viral aerosol formation and the cumulative nature of air saturation. As stated by Morawska et al. in Ref. [1] and recently recognized by WHO, "inhaling small airborne droplets is a probable third route of infection" in addition to transmission via larger respiratory droplets and direct contact with infected people or contaminated surfaces. Evidence of airborne transmission causing outbreaks in different enclosed environments was reported from the early stage of Covid-19 pandemics [2]. ...
... Past models based on Wells-Riley, although simplistic, have been proven sufficiently accurate to account for infections caused by measles, tubercolosi and influenza in confined and ventilated environments. A recent paper, authored by several experts in the field [1], elucidated how a possible mechanism for transmission of SARS-CoV2 in confined spaces would be the formation of "light" aerosol droplets (i.e. < 5 μm in diameter, unlike "heavy" droplets, over 5 μm) that diffuse in the environment after being produced by an infected person. ...
Issues linked to aerosol physics within school buildings and related infection risk still lack a proper recognition in school safety regulations. Limited spaces and limited available window-surfaces require to precisely investigate the seasonal airing factors and the occupancy/volume ratios in each classroom in order to assess the specific risk levels from viral loads of potentially infective sources. Moreover, most schools are still not provided with mechanical HVAC systems nor with air quality sensors. Fundamental questions are therefore: how the specific classroom volume and the specific airing cycle affects the long-range contagion risk in a given classroom? is linear social distancing the right way to assess a volumetric risk problem? We present here the results of an extended quantitative analysis based on the GN-Riley model applied to a real classroom scenario. The study illustrates, analyses and discusses the effectiveness of single and combined mitigation interventions, such as limiting class size, equipping teachers with microphones, increasing classroom volumes, and equipping classrooms with CO2 sensors. Moreover, we show experimental CO2 concentration data, measured in a real-life scenario, and propose a preliminary scheme for real-time infection risk assessment of SARS-CoV2 from aerosolization.
... In addition to contact and droplet transmission as well as fomite transmission (Doremalen et al., 2020), airborne transmission is considered to play a crucial role. Some publications even assume a dominant role of virus-laden airborne particles for SARS-CoV-2 transmission in some cases (Ma et al., 2020;Morawska & Milton, 2020;Stadnytskyi et al., 2020;R. Zhang et al., 2020; and a subordinate role in others (Klompas et al., 2020;Kim et al., 2020). ...
... Due to the large number of documented events in which infection with the Coronavirus occurred despite a large spatial distance between sender and recipient (Bae et al., 2020;Brlek et al., 2020;Cai et al., 2020;Charlotte, 2020;Groves et al., 2021;Hamner et al., 2020;Jang et al., 2020;Katelaris et al., 2021;Lendacki et al., 2021;Li et al., 2021;Lu et al., 2020;Mizumoto & Chowell, 2020;Moharir et al., 2021;Shen et al., 2020;Günther et al., 2020), as well as studies in which the viability of viruses in aerosols under laboratory conditions has been demonstrated to be as long as 16 hours (Fears et al., 2020) with a half-life of more than one hour (Doremalen et al., 2020), infection by viruses in airborne particles can be regarded as a serious route of spread. In their publication, signed by 239 scientists, (Morawska & Milton, 2020) urge more attention to be paid to the airborne spread of viruses. ...
In the wake of the SARS-CoV-2 pandemic, an increased risk of infection by virus-containing aerosols indoors is assumed. Especially in schools, the duration of stay is long and the number of people in the rooms is large, increasing the risk of infection. This problem particularly affects schools without pre-installed ventilation systems that are equipped with filters and/or operate with fresh air. Here, the aerosol concentration is reduced by natural ventilation. In this context, we are investigating the effect of large mobile air purifiers (AP) with HEPA filters on particle concentration and their suitability for classroom use in a primary school in Germany. The three tested APs differ significantly in their air outlet characteristics. Measurements of the number of particles, the particle size distribution, and the CO2 concentration were carried out in the classroom with students (April/May 2021) and with an aerosol generator without students. In this regard, the use of APs leads to a substantial reduction in aerosol particles. At the same time, the three APs are found to have differences in their particle decay rate, noise level, and flow velocity. In addition to the measurements, the effect of various influencing parameters on the potential inhaled particle dose was investigated using a calculation model. The parameters considered include the duration of stay, particle concentration in exhaled air, respiratory flow rate, virus lifetime, ventilation interval, ventilation efficiency, AP volumetric flow, as well as room size. Based on the resulting effect diagrams, significant recommendations can be derived for reducing the risk of infection from virus-laden aerosols. Finally, the measurements were compared to computational fluid dynamics (CFD) modeling, as such tools can aid the optimal placement and configuration of APs and can be used to study the effect of the spread of aerosols from a source in the classroom.
... In December 2019, a zoonotic outbreak of coronavirus disease 19 which is caused by SARS-CoV-2 emerged in Wuhan, Hubei province, China [4][5][6]. Like, SARS and MERS, COVID-19 is expected as an air borne disease and spreads human to human through microdroplets which are released during exhalation, talking, and coughing [7]. As it spread worldwide rapidly, WHO announced COVID-19 as a pandemic. ...
... Angiotensin converting enzyme (ACE) 2, a monocarboxypeptidage, is highly expressed on oral mucosa, respiratory tract, lung, kidney, pancreas, cardiovascular system, intestine, cerebral neuron, and immune cells (Fig. 1) [40][41][42]. ACE2 converts angiotensin II (Ang II) to angiotensin (1)(2)(3)(4)(5)(6)(7) [Ang (1-7)] and maintains a balance between them. Ang (1-7) interacts with Mas receptor (MasR) which facilitates the functions like vasodilation and anti-inflammation which are opposite to the angiotensin type 1 receptor (AT 1 R) mediated functions done by Ang II [43]. ...
The coronavirus disease 19 (COVID-19) has turned out to be a pandemic in short period of time due to the high transmissibility of its causative agent, severe acute respiratory syndrome coronavirus 2. Various reports have suggested the promising link between overexpression of angiotensin converting enzyme 2 (ACE2) and COVID-19 pathogenesis. The severity of COVID-19 pathophysiology is greatly depended on several comorbidities, like hypertension, diabetes mellitus (DM), respiratory and cardiovascular disease, out of which DM has emerged as a major risk factor. The current review focuses on the link among the expression of ACE2, use of ACE inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs), and risk of COVID-19 pathogenesis in DM. The review also emphasizes on synergistic detrimental effect of DM and COVID-19 on the immune system in provoking uncontrolled cytokine storm which eventually leads to lethal consequences. Finally, several possible therapeutic strategies have been highlighted to reduce the excess of risk associated with COVID-19 in people with DM.
... There is currently a broad consensus, endorsed by the WHO [7] and the CDC [8], that contagion of the SARS-CoV-2 virus occurs either by close range exposure to relatively large droplets emitted by infectious individuals or through indirect exposure to smaller submicron droplets denoted by the term "aerosols" (see, e.g., [9][10][11][12]), although the scope and relevance of each contagion route depend on local factors (volume, occupancy and ventilation regimes of inner spaces) [13][14][15][16][17][18]. The 5 µm cut-off separating larger droplets and "aerosols" is merely a convention that artificially simplifies droplet dynamics that vary along a continuous spectrum of diameters into two mutually exclusive modalities; thus, we avoid as much as possible the binary "droplets" vs. "aerosols" terminology. ...
... In fact, numerous aspects associated with the spreading and infection details of the SARS-CoV-2 virus remain uncertain and subject to large (often unexplained) individual and environmental variability (a good summary of these uncertainties is found in [13][14][15][16]). However, in order to be able to model a possible (previously unexplored) route of droplet transmission and possible infection, it is necessary and unavoidable to simplify this complexity and lack of data to obtain plausible order of magnitude estimates that can be verified once empiric evidence is available. ...
We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.
... COVID-19 is both deadly and highly transmissible. Recently, the airborne mode of COVID-19 transmission occurring primarily in indoor places has been recognized by many countries and research communities, suggesting proper mask use in transportation facilities such as cars and trains [4][5][6][7][8]. As of June 2021, the number of global confirmed cases is over 190 million, and the death toll is 3.9 million. ...
Serious traffic-related pollution and high population density during the spring festival (Chinese new year) travel rush (SFTR) increases the travelers’ exposure risk to pollutants and biohazards. This study investigates personal exposure to particulate matter (PM) mass concentration when commuting in five transportation modes during and after the 2020 SFTR: China railway high-speed train (CRH train), subway, bus, car, and walking. The routes are selected between Nanjing and Xuzhou, two major transportation hubs in the Yangtze Delta. The results indicate that personal exposure levels to PM on the CRH train are the lowest and relatively stable, and so it is recommended to take the CRH train back home during the SFTR to reduce the personal PM exposure. The exposure level to PM2.5 during SFTR is twice as high as the average level of Asia, and it is higher than the WHO air quality guideline (AQG).
... In mid-2020, around 240 scientists from 32 countries wrote an open letter to the World Health Organization (WHO) arguing that there was growing evidence for the spread of COVID-19 through opportunistic airborne transmission, especially in indoor environments with certain special uses (e.g., otorhinolaryngologic procedures) [11,12]. Around the same time, the National Health Commission, the State Administration of Traditional Chinese Medicine, and the WHO acknowledged the possibility of aerosol transmission in some indoor environments (e.g., due to insufficient ventilation, high aerosol concentrations) [13,14]. ...
Physical contact and respiratory droplet transmission have been widely regarded as the main routes of COVID-19 infection. However, mounting evidence has unveiled the risk of aerosol transmission of the virus. Whereas caution has been taken to avoid this risk in association with clinical facilities, facilities such as spa pools and Jacuzzis, which are characterized by bubble-aerosol generation, high bather loads, and limited turnover rates, may promote aerosol transmission. Focusing on these non-clinical facilities in the built environment, a review study was undertaken. First, the typical water disinfection and ventilation-aided operations for the facilities were illustrated. Second , cross comparisons were made between the applicable standards and guidelines of the World Health Organization and countries including Australia, Canada, China, the United Kingdom, and the United States. The similarities and differences in their water quality specifications, ventilation requirements, and air quality enhancement measures were identified; there were no specific regulations for preventing aerosol transmission at those aerosol-generating facilities. Third, a qualitative review of research publications revealed the emergence of studies on potential airborne transmission of COVID-19, but research on built facilities posing high risks of aerosol transmission remains scant. This study's results inform key directions for future research on abating aerosol transmission of COVID-19: the development of bespoke personal protective equipment and engineering and management controls on water quality, ventilation, and air quality.
... Fine aerosol particles with a diameter of 350 ± 6 nm were assessed because such aerosols are capable of spreading the virus at short to medium distances (several meters or entire room) as they remain suspended in the air (9,10). We chose to affix the masks on mannequin heads to more closely mimic reallife scenarios rather than merely test the filters to address the potential for leakage or penetration of the interface between the mask and the face. ...
Background: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic can spread through virus-containing aerosols ( ≤ 5 μm) and larger airborne droplets. Quantifying filtration efficiency of different kinds of masks and linings for aerosols that fall within the most penetrating particle size (80-400 nm) is critical to limiting viral transmission. The objective of our experiment was to compare the “real-world” filtering efficiency of different face masks for fine aerosols (350 nm) in laboratory simulations.
Methods: We performed a simulated bench test that measured the filtering efficiency of N95 vs. N99 masks with elastomeric lining in relation to baseline (“background”) aerosol generation. A mannequin head was placed within a chamber and was attached to an artificial lung simulator. Particles of known size (350 ± 6 nm aerodynamic diameter) were aerosolized into the chamber while simulating breathing at physiological settings of tidal volume, respiratory rate, and airflow. Particle counts were measured between the mannequin head and the lung simulator at the tracheal airway location.
Results: Baseline particle counts without a filter (background) were 2,935 ± 555 (SD) cm ⁻³ , while the N95 (1348 ± 92 cm ⁻³ ) and N99 mask with elastomeric lining (279 ± 164 cm ⁻³ ; p <0.0001) exhibit lower counts due to filtration.
Conclusion: The filtration efficiency of the N95 (54.1%) and N99 (90.5%) masks were lower than the filtration efficiency rating. N99 masks with elastomeric lining exhibit greater filtration efficiency than N95 masks without elastomeric lining and may be preferred to contain the spread of SARS-CoV-2 infection.
... The mode of spread of this virus is through direct contact with respiratory droplets of an infected individual. The virus is transmitted when the infected person coughs or sneezes and the virus reaches the eyes, nose or the mouth of a healthy individual 11 . The virus can survive on external surfaces for few minutes to few hours so one can also get infected in that way 3 In the beginning, the authorities in most of the countries imposed a strict lockdown to minimize the spread of virus. ...
Background: Corona Virus Disease 2019 (COVID-19) is a global pandemic still at large whose vaccination is in a trial phase. Dental practitioners are at high risk of exposure to this deadly epidemic. Therefore, the purpose of this study is to assess the knowledge and practice of dentists in the city of Multan, Pakistan. Method: This cross-sectional study was carried out in Multan, Pakistan from January to March 2021. A 30 items valid and reliable self-administrative questionnaire was used to assess the knowledge, practice, and source of information regarding the COVID-19 pandemic from dentists. Result: The results showed that the majority of dentists practicing in Multan had good knowledge (97.8%) and more than half of the respondents had good practice (65.6%). The most common source of their knowledge was WHO and Television. Almost half of the respondents showed fear of this virus in their practices. Conclusion: Dental practitioners of Multan revealed good knowledge regarding COVID-19. However, some key points were lacking in their knowledge and practice. Our findings have important implications for developing strategies that will improve the knowledge and practices of dentists in this region and also in whole country. Keywords: COVID-19, Coronavirus, Knowledge, Awareness, Dentists, Multan.
... Although there is ongoing debate, 13 it is assumed that similar risks for SARS CoV-2 transmission exist during the performance of AGPs, and in order to prevent inhalation of small particles, airborne and contact PPE (gown, N95 or P2 mask, gloves and eye protection) is recommended. ...
Objectives
To determine recommendations for the use of personal protective equipment (PPE) based on transmission risk for paediatric procedures in the Emergency Department during the COVID-19 pandemic. Methods
Two survey rounds were conducted in April-May 2020. The survey presented a number of emergency medicine procedures relevant to the care of children, and asked respondents to provide PPE recommendations according to levels of community transmission, and whether or not the child had symptoms of acute respiratory illness. ResultsParticipants were recruited by approaching relevant professional groups, with 15 from the PREDICT network and 12 from the Australasian Society of Infectious Diseases (ASID) Paediatric Infectious Diseases (ANZPID) Group. Airborne PPE is recommended for resuscitative procedures and various respiratory procedures in most situations There were differences in opinion between emergency and paediatric infectious disease specialists with regards to most appropriate PPE for children without symptoms of COVID-19 in a setting of low community transmission, and for procedures involving the head, neck or airway. In general, emergency physicians were more likely to favour airborne PPE than infectious disease specialists. In the setting of high community transmission, there was a stronger tendency to recommend at least droplet precautions for most procedures – regardless of whether or not the child had symptoms. Conclusions
Differences in PPE recommendations for various paediatric procedures between infectious disease specialists and emergency physicians were identified. Further research is urgently needed to clarify and quantify risks for many common interventions and determine strategies for multidisciplinary consensus regarding future recommendations.
... Foundational to infection control and prevention is a clear understanding of the modality of transmission of the contagion. For SARS-CoV-2, early during the COVID-19 pandemic, emphasis was placed on direct-contact and indirect-contact modes of transmission with recommendations focused on hand hygiene (WHO, 2020c) and physical distancing (WHO, 2020b); however, recognition of the longrange airborne route as a modality of transmission (Morawska and Milton, 2020;CDC, 2020b;Nardell and Nathavitharana, 2020;Morawska and Cao, 2020;Morawska et al., 2021) ...
Strong evidence exists indicating that aerosol transmission of the novel coronavirus SARS-CoV-2 is a significant transmission modality. We experimentally evaluated the impact of ventilation on aerosol dynamics and distribution along with the effective filtration efficiency (EFE) of four different mask types, with and without mask fitters, in a classroom setting. These were used to estimate aerosol conditional infection probability using the Wells-Riley model for three scenarios with different ventilation and mask interventions. Aerosol measurements confirmed that aerosol in the room was uniform within a factor of 2 for distances >2 m from the source. Mask EFE results demonstrate that most masks fit poorly with estimated leakage rates typically >50%. However, EFEs approaching the mask material FE were achievable using mask fitters. Infection probability estimates indicate that ventilation alone is not able to achieve probabilities <0.01 (1%). The use of moderate to high EFE masks reduces infection probability, > 5x in some cases. Reductions provided by ventilation and masks are synergistic and multiplicative. The results reinforce the use of properly donned masks to achieve reduced aerosol transmission of SARS-CoV-2 and other infectious diseases and motivate improvements in the EFE of masks through improved design or use of mask fitters.
... Small droplets or aerosols containing SARS-CoV-2 produced by talking and breathing may have a higher risk of transmission than larger droplets generated from sneezing and coughing. First, small particles can float in the air for a longer time without a specific cleaning process, such as ventilation or air purification [3,[7][8][9][10], and this longer residence time in the air significantly increases the probability of inhalation by a susceptible person [11]. Moreover, many studies have reported that talking and breathing produce a considerable number of particles, which can significantly influence airborne infections [12][13][14][15][16][17]. ...
The transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurs via contact with contaminated surfaces and inhalation of large airborne droplets and aerosols. As growing evidence of airborne SARS-CoV-2 transmission has been reported worldwide, ventilation is an effective method of reducing the infection probability of SARS-CoV-2. This leads to such questions as “What is a sufficient ventilation rate for avoiding the risk of COVID-19 infection?” Therefore, this study evaluates the critical ventilation rates according to room size and exposure time when a susceptible person is in the same room as an infector. The analytical results were based on data obtained from 70 confirmed COVID-19 cases transmitted in confined spaces without an operational ventilation system. The results reveal that even with active ventilation (20 h−1 air exchange rate), the critical exposure time for a susceptible person with a COVID-19 infector in a small space of 20 m3 is less than 1 h. For other cases (different space sizes), the estimated air exchange rates for avoiding the risk of infection are generally higher than various requirements for good indoor air quality. The findings of this study will provide guidelines for determining sufficient ventilation rates to protect against the highly contagious COVID-19.
... Avenues for future research Findings highlight the need for evaluations of interventions to support people to avoid touching the T-Zone, disinfect surfaces, maintain physical distancing, and ensure efficient ventilation. Ventilation is increasingly seen as an important personal protective behaviour but was missed from the present review as it was planned during an earlier epidemic phase when the emphasis was on viral transmission via droplets rather than aerosols (Anderson, Turnham, Griffin, & Clarke, 2020;Morawska & Milton, 2020). In addition, we need studies designed to detect effects on behavioural outcomes and data on the affordability and equity of interventions to increase personal protective behaviours, particularly in low-and middle-income countries. ...
Increasing personal protective behaviours is critical for stopping the spread of respiratory viruses, including SARS‐CoV‐2: We need evidence to inform how to achieve this. We aimed to synthesize evidence on interventions to increase six personal protective behaviours (e.g., hand hygiene, face mask use, maintaining physical distancing) to limit the spread of respiratory viruses. We used best practice for rapid evidence reviews. We searched Ovid MEDLINE and Scopus. Studies conducted in adults or children with active or passive comparators were included. We extracted data on study design, intervention content, mode of delivery, population, setting, mechanism(s) of action, acceptability, practicability, effectiveness, affordability, spill‐over effects, and equity impact. Study quality was assessed with Cochrane’s risk‐of‐bias tool. A narrative synthesis and random‐effects meta‐analyses were conducted. We identified 39 studies conducted across 15 countries. Interventions targeted hand hygiene (n = 30) and/or face mask use (n = 12) and used two‐ or three‐arm study designs with passive comparators. Interventions were typically delivered face‐to‐face and included a median of three behaviour change techniques. The quality of included studies was low. Interventions to increase hand hygiene (k = 6) had a medium, positive effect (d = .62, 95% CI = 0.43–0.80, p < .001, I2 = 81.2%). Interventions targeting face mask use (k = 4) had mixed results, with an imprecise pooled estimate (OR = 4.14, 95% CI = 1.24–13.79, p < .001, I2 = 89.67%). Between‐study heterogeneity was high. We found low‐quality evidence for positive effects of interventions targeting hand hygiene, with unclear results for interventions targeting face mask use. There was a lack of evidence for most behaviours of interest within this review.
... Mitigation of risk was partially attained by following the university's requirement of wearing face coverings and maintaining social distance for every person involved in testing. We further attempted to minimize the production of small speech droplets, which can cause airborne transmission of COVID-19 in confined environments [7][8][9][10]. Moreover, as speaking under face coverings imposes vocal fatigue and discomfort, difficulties in coordinating speech and breathing, and can make speech more difficult to understand [11], our goal was to reduce the need for speaking by the experimenter. ...
The COVID-19 pandemic resulted in suspending in-person human subject research across most institutions in the US. Our extensive cognitive assessment for a phase-2 clinical trial, Physical Activity and Alzheimer's Disease–2 (PAAD-2), was also paused in March 2020. It was important to identify strategies to mitigate the risk of COVID-19 transmission during our testing, which initially required substantial human speech and close person-to-person contact for test directions and instant feedback on paper/pencil tests. Given current understanding of the COVID-19 transmission, we dramatically adjusted the testing protocol to minimize the production of speech droplets and allow social distancing while maintaining the integrity of testing. We adopted state-of-the-art speech synthesis and computerization techniques to create an avatar to speak on behalf of the experimenter for all verbal instructions/feedback, used a document camera to observe the paper/pencil tests from the required distances, and automated the testing sequence and timing. This paper aims 1) to describe an innovative laboratory-based cognitive testing protocol for a completely contact-free, computer-speaking, and semi-automated administration; and 2) to evaluate the integrity of the modified protocol (n = 37) compared with the original protocol (n = 32). We have successfully operated the modified protocol since July 2020 with no evidence of COVID-19 transmission during testing, and data support that the modified protocol is robust and captures data identical to the original protocol. This transition of data collection methods has been critical during the pandemic and will be useful in future studies to mitigate the risk of contagious disease transmission and standardize laboratory-based psychological tests.
Trial registration: ClinicalTrials.gov NCT03876314. Registered March 15, 2019
... Recently, however, scientists have urged public-health authorities to acknowledge the potential for airborne transmission of the novel SARS-CoV-2 coronavirus [1]. While there is still a lot that is unknown about the transmission of the SARS-CoV-2 virus, it is evident now that like its predecessor, a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 SARS-CoV-1, airborne transmission is a significant mode of transmission [2][3][4]. Airborne transmission happens when a susceptible person inhales microscopic bio-aerosols in the air which are generated from a respiratory event such as a cough, sneeze, or even just breathing and talking [2,5]. While larger droplets (�100μm) reach the ground within a second, aerosols can linger in the air for hours, increasing the probability of a susceptible person coming in contact with the virus [6,7]. ...
The use of face masks by the general population during viral outbreaks such as the COVID-19 pandemic, although at times controversial, has been effective in slowing down the spread of the virus. The extent to which face masks mitigate the transmission is highly dependent on how well the mask fits each individual. The fit of simple cloth masks on the face, as well as the resulting perimeter leakage and face mask efficacy, are expected to be highly dependent on the type of mask and facial topology. However, this effect has, to date, not been adequately examined and quantified. Here, we propose a framework to study the efficacy of different mask designs based on a quasi-static mechanical model of the deployment of face masks onto a wide range of faces. To illustrate the capabilities of the proposed framework, we explore a simple rectangular cloth mask on a large virtual population of subjects generated from a 3D morphable face model. The effect of weight, age, gender, and height on the mask fit is studied. The Centers for Disease Control and Prevention (CDC) recommended homemade cloth mask design was used as a basis for comparison and was found not to be the most effective design for all subjects. We highlight the importance of designing masks accounting for the widely varying population of faces. Metrics based on aerodynamic principles were used to determine that thin, feminine, and young faces were shown to benefit from mask sizes smaller than that recommended by the CDC. Besides mask size, side-edge tuck-in, or pleating, of the masks as a design parameter was also studied and found to have the potential to cause a larger localized gap opening.
... The current COVID-19 pandemic has claimed over 3.9 million lives and infected another 184 million globally, as at 7 th July 2021 (WHO, 2021). The primary mode of transmission of the SARS-CoV-2 virus, the causative agent for COVID-19, is through respiratory droplets Cai et al., 2020;Bahl et al., 2020;Morawska and Milton, 2020). This has led to the implementation of mitigation measures, such as social distancing and the use of face masks WHO, 2020;Howard et al., 2020;Dalton et al., 2020;Viner et al., 2020). ...
Contamination of contact surfaces with SARS-CoV-2 has been reported as a potential route for the transmission of COVID-19. This could be a major issue in developing countries where access to basic sanitation is poor, leading to the sharing of toilet facilities. In this study, we report SARS-CoV-2 contamination of key contact surfaces in shared toilets and the probabilistic risks of COVID-19 infections based on detection and quantification of the nucleic acid on the surfaces. We observed that 54–69% of the contact surfaces were contaminated, with SARS-CoV-2 loads ranging from 28.1 to 132.7 gene copies per cm². Toilet seats had the highest contamination, which could be attributed to shedding of the virus in feces and urine. We observed a significant reduction in viral loads on the contaminated surfaces after cleaning, showing the potential of effective cleaning on the reduction of contamination. The pattern of contamination indicates that the most contaminated surfaces are those that are either commonly touched by users of the shared toilets or easily contaminated with feces and urine. These surfaces were the toilet seats, cistern handles and tap handles. The likelihood (probability) of infection with COVID-19 on these surfaces was highest on the toilet seat (1.76 × 10⁻⁴(1.58 × 10⁻⁶)) for one time use of the toilet. These findings highlight the potential risks for COVID-19 infections in the event that intact infectious viral particles are deposited on these contact surfaces. Therefore, this study shows that shared toilet facilities in densely populated areas could lead to an increase in risks of COVID-19 infections. This calls for the implementation of risk reduction measures, such as regular washing of hands with soap, strict adherence to wearing face masks, and effective and regular cleaning of shared facilities.
... Extraversion, in addition, is one of the Big Five personality traits used extensively in psychology 8 and may also drive social behaviours that account for infection. Height has been associated both with health and income [9][10][11][12] and is included as a further control. In our analyses, sex and age are also included following research on mortality and may also be connected to transmission. ...
Objective
To develop evidence of work-related and personal predictors of COVID-19 transmission.
Setting and respondents
Data are drawn from a population survey of individuals in the USA and UK conducted in June 2020.
Background methods
Regression models are estimated for 1467 individuals in which reported evidence of infection depends on work-related factors as well as a variety of personal controls.
Results
The following themes emerge from the analysis. First, a range of work-related factors are significant sources of variation in COVID-19 infection as indicated by self-reports of medical diagnosis or symptoms. This includes evidence about workplace types, consultation about safety and union membership. The partial effect of transport-related employment in regression models makes the chance of infection over three times more likely while in univariate analyses, transport-related work increases the risk of infection by over 40 times in the USA. Second, there is evidence that some home-related factors are significant predictors of infection, most notably the sharing of accommodation or a kitchen. Third, there is some evidence that behavioural factors and personal traits (including risk preference, extraversion and height) are also important.
Conclusions
The paper concludes that predictors of transmission relate to work, transport, home and personal factors. Transport-related work settings are by far the greatest source of risk and so should be a focus of prevention policies. In addition, surveys of the sort developed in this paper are an important source of information on transmission pathways within the community.
... Although the exact routes of transmission for SARS-CoV-2 are still contentious, analysis of known "superspreading events" within social situations, including a restaurant and a choir practice, strongly suggest that airborne transmission plays a significant role (4)(5)(6)(7). Droplets containing infective viral loads can travel up to 250 m before hitting the ground, depending on droplet size, velocity, and air flow, with spreading in poorly ventilated indoor areas thought to be the most prevalent (8,9). ...
The COVID-19 global pandemic, as well as the widespread persistence of influenza and the common cold, create the need for new medical devices such as nasal sprays to prevent viral infection and transmission. Carrageenan, a sulfated polysaccharide, has a broad, non-pharmacological antiviral capacity, however it performs poorly in two key areas; spray coverage and mucoadhesion. Therefore gellan, another polysaccharide, was investigated as an excipient to improve these properties. It was found that viscoelastic relaxation time was the key predictor of spray coverage, and by reducing this value from 2.5 to 0.25 s, a mix of gellan and carrageenan gave more than four times the coverage of carrageenan alone (p < 0.0001). Gellan also demonstrated enhanced adhesion to a mucus analog that increased significantly with time (p < 0.0001), suggesting the development of specific gellan–mucin interactions. This property was conferred to carrageenan on mixing the two polymers. Together, this data suggests that gellan is a promising excipient to improve both sprayability and mucoadhesion of carrageenan for use in antiviral nasal sprays.
... Inhalation of microscopic respiratory droplets containing viruses is possible at short-range to long-range distances. 16 The higher the concentration of infectious particles, and thus greater the risk of infection, at a short-range from an infectious source (<1 m) is significantly higher than that at a long range (>2 m). 1 However, despite this, short-range airborne transmission routes have largely been overlooked. 17 Infectious pathogens filled with lung fluid spread via respiratory droplets. ...
Increasing evidence supports the significant role of short-range airborne transmission of viruses when in close contact with a source patient. A full-scale ventilated room (Cleanliness: ISO 14644–1 Class 5) and two face-to-face standing breathing thermal manikins were used to simulate a source individual and a susceptible person. Monodisperse particle generation and measurement techniques were used to evaluate the effect of virus-laden droplet nuclei size on short-range airborne transmission risk. We analysed four particle sizes (1.0, 1.5, 2.5, and 5.0 µm) to simulate the transport of exhaled droplet nuclei within an interpersonal distance of 0.5 m. The results indicated that the size distribution of airborne droplet nuclei could significantly influence transmission, with the inhalation fraction decreasing with increasing droplet nuclei size. Additionally, results showed that proximity to the source manikin could influence transmission. Inhalation fraction decreased with increasing interpersonal distance, fitting well with the 1/ d rule of droplet nuclei concentration decay. Our findings improve the understanding of the mechanism of the disease transmission.
... 3 The common routes for SARS-CoV-2 spread include (i) airborne transmission through inhalation of droplets and aerosols and (ii) direct contact transmission from the exposure of conjunctival, nasal, or oral mucosae to contaminated body fluids. [6][7][8] Even though droplet nuclei (1-5 lm), aerosols (<50 lm), droplets, and splatter (>50 lm) have been commonly used to describe gas-based colloidal suspensions containing dispersed particles [either liquid (water, saliva, blood, sputum) or solid (bacteria, virus, fungus, and dental plaque)], [9][10][11] recent reports have indicated an urgent need to harmonize discussions about modes of virus transmission across disciplines by clarifying the terminology used to distinguish between aerosols and droplets. According to these studies, a threshold of 100 lm should be used because this size more effectively separates particles' aerodynamic behavior, [12][13][14] and their ability to inhale can be used to determine the utility of engineering controls and strategies while providing clear guidance to the public. ...
The coronavirus disease 2019 pandemic has imposed unprecedented occupational challenges for healthcare professionals. In dentistry, handheld instruments such as air and electric handpieces, ultrasonic scalers, and air/water syringes are capable of generating aerosols, droplets, and splatter, thereby exposing dental professionals to airborne contaminants such as viruses, bacteria, and fungi. The objective of the present study was to determine the spatial distribution of aerosols by size (0.30 to 20.00 lm) and the efficacy of a novel aerosol containment device (ACD) in a large operatory room with 12 dental chairs. Real-time portable laser aerosol spectrometers were used to measure the size-resolved number concentration of aerosols generated by a collision nebulizer. Results reported demonstrate that aerosol number concentrations significantly decreased as a function of distance with or without the utilization of the ACD. The ACD was able to efficiently decrease (up to 8.56-fold) the number and size distribution of particles in a large dental clinic. The novel device demonstrated higher efficiency for particles shown to contain the highest levels of severe acute respiratory syndrome coronavirus 2 in Chinese hospitals, thereby showing great promise to potentially decrease the spreading of nosocomial pathogens in dental settings.
... The observation that transmission in outdoor settings is at least an order of magnitude lower than indoors [23] strongly suggests that the airborne route is key. Indeed, consensus among aerosol experts has emerged that transfer of respiratory secretions through the air dominates the SARS-CoV-2 transmission pathway [24]. ...
The SARS-CoV-2 virus is highly contagious, as demonstrated by numerous well-documented superspreading events. The infection commonly starts in the upper respiratory tract (URT) but can migrate to the lower respiratory tract (LRT) and other organs, often with severe consequences. Whereas LRT infection can lead to shedding of virus via breath and cough droplets, URT infection enables shedding via abundant speech droplets. Their viral load can be high in carriers with mild or no symptoms, an observation linked to the abundance of SARS-CoV-2-susceptible cells in the oral cavity epithelium. Expelled droplets rapidly lose water through evaporation, with the smaller ones transforming into long-lived aerosol. Although the largest speech droplets can carry more virions, they are few in number, fall to the ground rapidly and therefore play a relatively minor role in transmission. Of more concern is small speech aerosol, which can descend deep into the LRT and cause severe disease. However, since their total volume is small, the amount of virus they carry is low. Nevertheless, in closed environments with inadequate ventilation, they can accumulate, which elevates the risk of direct LRT infection. Of most concern is the large fraction of speech aerosol that is intermediate-sized because it remains suspended in air for minutes and can be transported over considerable distances by convective air currents. The abundance of this speech-generated aerosol, combined with its high viral load in pre- and asymptomatic individuals, strongly implicates airborne transmission of SARS-CoV-2 through speech as the primary contributor to its rapid spread.
Abstract
... The reservations expressed by mothers about the possibility of transmission of the virus via breast milk would be to raise awareness among communities by the government and other partners about the means and mode of transmission of the infection, the possibility of mother-to-child transmission of which is not included. The WHO confirms that to date, no transmission of the COVID-19 virus through breast milk and breastfeeding has been observed Page Recent studies related to air pollution have reported that the new coronavirus could survive in ambient air for several hours and potentially be transmitted by aerosols, especially in closed indoor environments with limited social distance and poor ventilation [33,34,35]. When breastfeeding in public squares, mothers may wear cloth masks or masks to protect themselves from breathable virus carriers in the air, while their infants may not wear any respiratory protection to avoid direct exposure to indoor air. ...
Introduction: COVID-19 presents immediate and long-term nutritional challenges. Improving infant and young children feeding (IYCF) at the community level is a key priority for optimizing the survival, growth, and development of children. The study assessed the influence of the Covid-19 pandemic on the feeding behaviors and practices of children under five in households of the Mifi Health District. Methods: This qualitative study used the non-random sampling technique; data was collected during focus groups (FG) among mothers & fathers, face-to-face individual interviews with Key informants (KI), and In-depth interviews (ID), and document review. Discussions were transcribed verbatim and repeated data was deleted. A thematic analysis was carried out. Results: Forty-five participants (76% Female; 24% male), 03 FG, and 30 face-to-face individual interviews were conducted (15 KI; 15 ID). Demographically, 82.2% were Christians; 11.1% Muslims and 6.7% traditionalists. Mothers knew that it’s necessary to exclusively breastfeed children up to six months and incorporate complementary foods beyond six months even during COVID19. They however believe that breastfeeding in public places exposes babies to COVID19; complementary foods from markets are a potential source of infection and an infected mother should not breastfeed. Participants mentioned a reduction in the consumption of meat and fruit in households. The spread of rumors led to increased demand for foodstuff. Mothers reported the need to wash their hands and wear face masks before breastfeeding. Equally, a decrease in attendance of vaccination services was noted. Conclusion: Creating breastfeeding rooms in public places and an intensive sensitization on nutrition in the COVID19 context can improve IYCF.
... The face-to-face return to classrooms in Spain in September 2020 during the global pandemic and after a long period of confinement opened up a debate in society about health security and air quality. The discussion was reinforced when the scientific community began to show evidence of greater transmission by aerosols than by fomites [1]. Poor indoor air quality (IAQ) was already an existing problem in naturally ventilated schools, but awareness was only raised after the COVID crisis. ...
This paper describes the implementation of a series of ventilation strategies in a nursery and primary school from September 2020, when the government decided to resume the students’ face-to-face activity in the middle of a COVID scenario. Air quality and hygrothermal comfort conditions were analysed before the pandemic and compared for different ventilation configurations in a post-COVID scenario. Ventilation strategies included the protocols issued by the Public Administration, while others were developed based on the typological configuration and use of the school. Results revealed that it is advisable to implement certain strategies that reduce the risk of infection among the occupants of the spaces, without a significant decrease in hygrothermal comfort. Given the importance of maintaining better IAQ in the future within classrooms, and regarding the pre-COVID situation, these strategies may be extended beyond this pandemic period, through a simple protocol and necessary didactic package to be assumed by both teachers and students of the centre.
... [2][3][4][5][6] Even so, the risks posed by airborne spread remain poorly addressed by many safety standards, 7 a trend that continued with dire consequences during the early phases of the COVID-19 pandemic. 8 It is now apparent that transmission of SARS-CoV-2, the virus causing COVID-19, occurs primarily through the inhalation of airborne virions, 9,10 as opposed to impaction to a susceptible persons eyes, nostrils, and lips. ...
Some infectious diseases, such as influenza, tuberculosis, and SARS‐CoV‐2, may be transmitted when virus‐laden particles expelled from an infectious person are inhaled by someone else, which is known as the airborne transmission route. These virus‐laden particles are more concentrated in the expiratory jet of an infectious person than elsewhere in a well‐mixed room, but this near‐field enhancement in virion exposure has not been well quantified. Transmission of airborne viruses depends on factors that are inherently variable and, in many cases, poorly constrained, and quantifying this uncertainty requires large ensembles of model simulations that span the variability in input parameters. However, models that are well‐suited to simulate the near‐field evolution of respiratory particles are also computationally expensive, which limits the exploration of parametric uncertainty. In order to perform many simulations that span the wide variability in factors governing airborne transmission, we developed the Quadrature‐based model of Respiratory Aerosol and Droplets (QuaRAD). QuaRAD is an efficient framework for simulating the evolution of virus‐laden particles after they are expelled from an infectious person, their deposition to the nasal cavity of a susceptible person, and the subsequent risk of initial infection. We simulated 10 000 scenarios to quantify the risk of initial infection by a particular virus, SARS‐CoV‐2. The predicted risk of infection was highly variable among scenarios and, in each scenario, was strongly enhanced near the infectious individual. In more than 50% of scenarios, the physical distancing needed to avoid near‐field enhancements in airborne transmission was beyond the recommended safe distance of two meters (six feet) if the infectious person is not wearing a mask, though this distance defining the near‐field extent was also highly variable among scenarios; the variability in the near‐field extent is explained predominantly by variability in expiration velocity. Our findings suggest that maintaining at least two meters of distance from an infectious person greatly reduces exposure to airborne virions; protections against airborne transmission, such as N95 respirators, should be available when distancing is not possible.
... The most recent investigation, in an experimental context, points to the new coronavirus remaining up to 72 hours in plastic and stainless steel with temperatures of around 20º and humidity of 40% [33,34]. Other multiple investigations have already reported that SARS-CoV-2 and other coronaviruses are able to remain on surfaces such as metal, glass, PVC, Teflon, and other materials, for several days [35,36,37,38]. ...
Coronaviruses have been responsible for major epidemic crises in 2003 with SARS-CoV-1, in 2012 with MERS-CoV and in 2019 with SARS-CoV-2 (COVID-19), causing serious atypical pneumonia in humans. We intend, with this systematic analysis and meta-analysis, to clarify the prevalence of the various strains of coronavirus in different animal species. For this purpose, we carried out an electronic survey using Pubmed's Veterinary Science search tool to conduct a systematic assessment of published studies reporting the prevalence of different strains of coronavirus in different animal species between 2015 and 2020. We conducted different analysis to assess sensitivity, publication bias, and heterogeneity, using random and fixed effects. The final meta-analysis included 42 studies for systematic review and 29 in the meta-analysis. For the geographic regions with a prevalence greater than or equal to 0.20 (Forest plot overall; prevalence = 0.20, p < 0.01, Q = 10476.22 and I2 = 100%), the most commonly detected viruses were: enteric coronavirus (ECoV), pigeon-dominant coronavirus, (PdCoV), Avian coronavirus M41, Avian coronavirus C46, Avian coronavirus A99, Avian coronavirus JMK, MERS-CoV, Bovine coronavirus, Ro-BatCoV GCCDC1, Alphacoronavirus, Betacoronavirus, Deltacoronavirus, Gamacoronavirus and human coronaviruses (HCoVs). The wide presence of different strains of coronavirus in different animal species on all continents demonstrates the great biodiversity and ubiquity of these viruses.
The most recent epidemiological crises caused by coronavirus demonstrates our unpreparedness to anticipate and mitigate emerging risks, as well as the need to implement new epidemiological surveillance programs for viruses. Combined with the need to create advanced training courses in One Health, this is paramount in order to ensure greater effectiveness in fighting the next pandemics.
... COVID-19 can be transmitted via different routes, including virus-laden particles aerosolized due to human activities such as breathing, speaking, singing, coughing, sneezing, etc. (Bahlet al., 2021;CDC, 2021;Ma et al., 2021;Morawska & Cao, 2020;Morawska & Milton, 2020;Schijven et al., 2021). Better recognized for producing larger droplets, coughing and sneezing also aerosolize tremendous amounts of small aerosol particles (Lindsley et al., 2012;Han et al., 2013), primarily in the sub-micrometer size range. ...
COVID-19 is spread via different routes, including virus-laden airborne particles generated by human respiratory activities. In addition to large droplets, coughing and sneezing produce a lot of small aerosol particles. While face coverings are believed to reduce the aerosol transmission, information about their outward effectiveness is limited. Here, we determined the aerosol concentration patterns around a coughing and sneezing manikin and established spatial zones representing specific elevations of the aerosol concentration relative to the background. Real-time measurements of sub-micrometer aerosol particles were performed in the vicinity of the manikin. The tests were carried out without any face covering and with three different types of face covers: a safety faceshield, low-efficiency facemask and high-efficiency surgical mask. With no face covering, the simulated coughing and sneezing created a powerful forward-propagating fine aerosol flow. At 6 ft forward from the manikin head, the aerosol concentration was still 20-fold above the background. Adding a face covering reconfigured the forward-directed aerosol transmission pattern. The tested face coverings were found capable of mitigating the risk of coronavirus transmission; their effectiveness is dependent on the protective device. The outward leakage associated with a specific face covering was shown to be a major determinant of the exposure level for a person standing or seating next to or behind the coughing or sneezing “spreader” in a bus/train/aircraft/auditorium setting. Along with reports recently published in the literature, the study findings help assess the infectious dose and ultimately health risk for persons located within a 6-ft radius around the “spreader.”
... An infected person may pass on the virus to the next individual through the surface of an object that the person come in contact with, and more likely so if the latter touches the nose, mouth or the eyes. In contrast to past global epidemic like SARS, or MERS, COVID-19 is an airborne and highly virulent respiratory disease with long incubation period (Morawska and Milton 2020). Indoor venues, places with poor ventilation, and where people linger around longer are more prone to transmission (Lewis 2020). ...
The COVID-19 epidemic has unleashed a trail of health and economic destruction since the first infected patient was reported in Wuhan, China in late 2019. While this disease is seemingly not as deadly compared to SARS, Ebola, or MERS, it is an exceptionally virulent plague. Evidence has suggested that certain segments of the population and environmental attributes are more vulnerable. Specifically, the elderly people and those with pre-existing medical conditions reported the highest morbidity from COVID-19 infection. Places that are densely populated, with voluminous human traffic, and fleeting social interactions are ostensibly most conducive for viral transmission. Geospatial networks with high centrality and transitivity such as public transportations, leisure and recreational spaces, and workplaces, are locations most susceptible to COVID-19. In response to this epidemic, Singapore entered into a lockdown to curb the spread. All but essential workers such as those in healthcare, public services, and critical supply chains, were required to work from home and minimize interpersonal contact. This study aims to understand local vulnerability by introducing changes of risks and human mobilities across space and time. The study develops a socio-ecological framework of epidemiology using a set of social, built, and spatial features known to influence disease transmission. Subzones with higher integrated vulnerabilities could receive greater epidemiological attention and support in future pandemics.
... It states that there is 'consistent, strong evidence that SARS-CoV-2 spreads by airborne transmission', and although other types of transmission might contribute, Greenhalgh et al. (2021Greenhalgh et al. ( : 1604 believe that, 'the airborne route is likely to be dominant'. Similarly, Morawska & Milton (2020: 2311 write that: ...
Airborne transmission of virus via respiratory aerosols plays an important role in the spread of infectious diseases in indoor environments. Ventilation and social distancing are two major control strategies to reduce the indoor airborne infection risk. However, there is a present lack of science-based information on how the human exposure to viral aerosols vary with ventilation condition and social distance. The objective of this study is to explore the transport patterns of respiratory aerosols in occupied spaces and assess the occupant exposure risk under different ventilation strategies, social distances and aerosol emission modes. The CFD simulation results show that buoyancy-driven flow regime (can be found in many residential settings) can lead to longer transmission distance of exhaled aerosols than the mixing airflow, thereby causing higher cross-infection risk in indoor environments. The results also suggest that a 2 m (6 ft) social distance alone may not ensure control of indoor airborne infections.
Objective
To study the airflow, transmission and clearance of aerosols in the clinical spaces of a hospital ward that had been used to care for patients with COVID-19, and to examine the impact of portable air cleaners on aerosol clearance.
Design
Observational study.
Setting
A single ward of a tertiary public hospital in Melbourne Australia.
Intervention
Glycerine-based aerosol was used as a surrogate for respiratory aerosols. The transmission of aerosols from a single patient room into corridors and a nurses’ station in the ward was measured. The rate of clearance of aerosols was measured over time from the patient room, nurses’ station and ward corridors with and without air cleaners (also called portable HEPA filters).
Results
Aerosols rapidly travelled from the patient room into other parts of the ward. Air cleaners were effective in increasing the clearance of aerosols from the air in clinical spaces and reducing their spread to other areas. With two small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes.
Conclusion
Air cleaners may be useful in clinical spaces to help reduce the risk of healthcare acquired acquisition of respiratory viruses that are transmitted via aerosols. They are easy to deploy and are likely to be cost effective in a variety of healthcare settings.
Since the start of the COVID-19 pandemic, experts and the broader public have vigorously debated the means by which SARS CoV-2 is spread. And understandably so, for identifying the routes of transmission is crucial for selecting appropriate nonpharmaceutical interventions to control the pandemic. The most controversial question in the debate is the role played by airborne transmission. What is at stake is not just the clinical evidence, but the implications for public health policy, society, and psychology. Interestingly, however, the issue of airborne transmission is not a new controversy. It has reappeared throughout the history of western medicine. This essay traces the notion of airborne infection from its development in ancient medical theories to its manifestation in the modern era and its impact today.
Face masks reduce the expulsion of respiratory aerosols produced during coughs and exhalations (“source control”). Factors such as the directions in which people are facing (orientation) and separation distance also affect aerosol dispersion. However, it is not clear how the combined effects of masking, orientation, and distance affect the exposure of individuals to respiratory aerosols in indoor spaces. We placed a respiratory aerosol simulator (“source”) and a breathing simulator (“recipient”) in a 3 m x 3 m chamber and measured aerosol concentrations for different combinations of masking, orientation, and separation distance. When the simulators were front-to-front during coughing, masks reduced the 15-minute mean aerosol concentration at the recipient by 92% at 0.9 and 1.8 m separation. When the simulators were side-by-side, masks reduced the concentration by 81% at 0.9 m and 78% at 1.8 m. During breathing, masks reduced the aerosol concentration by 66% when front-to-front and 76% when side-by-side at 0.9 m. Similar results were seen at 1.8 m. When the simulators were unmasked, changing the orientations from front-to-front to side-by-side reduced the cough aerosol concentration by 59% at 0.9 m and 60% at 1.8 m. When both simulators were masked, changing the orientations did not significantly change the concentration at either distance during coughing or breathing. Increasing the distance between the simulators from 0.9 m to 1.8 m during coughing reduced the aerosol concentration by 25% when no masks were worn but had little effect when both simulators were masked. During breathing, when neither simulator was masked, increasing the separation reduced the concentration by 13%, which approached significance, while the change was not significant when both source and recipient were masked. Our results show that universal masking reduces exposure to respiratory aerosol particles regardless of the orientation and separation distance between the source and recipient.
Introduction: Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). On March 11, 2020, the World Health Organization declared a coronavirus pandemic. Despite the intensive research in the epidemiology and prevention of the disease, there is a lack of information on specific risk groups (such as children) that could facilitate informed decisions on the implementation of appropriate and sufficient anti- epidemic measures to ensure the greatest possible social functioning with the least possible risk to the population.
Objective: To analyze the specific features of the prevalence, prevention, and course of the disease in children and the influence of educational institutions in these processes.
Material and methods: A literature search which covered the published data until 31 March 2021 was conducted in worldwide databases for medical literature (PubMed and Google Scholar). The results were analyzed for eligibility, and those that included endpoints relevant to the task were included in the analysis.
Results: We found no convincing evidence of an increased risk of serious COVID-19 in adults living with children compared to households without children. There was evidence of a slightly increased risk of SARS- CoV-2 infection in adults living with older children. Non-pharmacological interventions in schools to prevent SARS-CoV-2 transmission play a role, but it is not possible to assess the effectiveness of individual measures. Schools are not a high-risk environment for the transmission of the infection. There was no evidence of a difference in the severity of the disease depending on the presence of symptoms in the source of the infection.
Conclusion: Termination of the traditional learning process to control the COVID-19 pandemic should be done only as an anti-epidemic measure of last resort.
Objective
To assess the SARS-CoV-2 transmission in healthcare workers (HCWs) using seroprevalence as a surrogate marker of infection in our tertiary care centre according to exposure.
Design
Seroprevalence cross-sectional study.
Setting
Single centre at the end of the first COVID-19 wave in Lausanne, Switzerland.
Participants
1874 of 4074 responders randomly selected (46% response rate), stratified by work category among the 13 474 (13.9%) HCWs.
Main outcome measures
Evaluation of SARS-CoV-2 serostatus paired with a questionnaire of SARS-CoV-2 acquisition risk factors internal and external to the workplace.
Results
The overall SARS-CoV-2 seroprevalence rate among HCWs was 10.0% (95% CI 8.7% to 11.5%). HCWs with daily patient contact did not experience increased rates of seropositivity relative to those without (10.3% vs 9.6%, respectively, p=0.64). HCWs with direct contact with patients with COVID-19 or working in COVID-19 units did not experience increased seropositivity rates relative to their counterparts (10.4% vs 9.8%, p=0.69 and 10.6% vs 9.9%, p=0.69, respectively). However, specific locations of contact with patients irrespective of COVID-19 status—in patient rooms or reception areas—did correlate with increased rates of seropositivity (11.9% vs 7.5%, p=0.019 and 14.3% vs 9.2%, p=0.025, respectively). In contrast, HCWs with a suspected or proven SARS-CoV-2-infected household contact had significantly higher seropositivity rates than those without such contacts (19.0% vs 8.7%, p<0.001 and 42.1% vs 9.4%, p<0.001, respectively). Finally, consistent use of a mask on public transportation correlated with decreased seroprevalence (5.3% for mask users vs 11.2% for intermittent or no mask use, p=0.030).
Conclusions
The overall seroprevalence was 10% without significant differences in seroprevalence between HCWs exposed to patients with COVID-19 and HCWs not exposed. This suggests that, once fully in place, protective measures limited SARS-CoV-2 occupational acquisition within the hospital environment. SARS-CoV-2 seroconversion among HCWs was associated primarily with community risk factors, particularly household transmission.
Objective
To determine if oesophago-gastro-duodenoscopy (OGD) generates increased levels of aerosol in conscious patients and identify the source events.
Design
A prospective, environmental aerosol monitoring study, undertaken in an ultraclean environment, on patients undergoing OGD. Sampling was performed 20 cm away from the patient’s mouth using an optical particle sizer. Aerosol levels during OGD were compared with tidal breathing and voluntary coughs within subject.
Results
Patients undergoing bariatric surgical assessment were recruited (mean body mass index 44 and mean age 40 years, n=15). A low background particle concentration in theatres (3 L ⁻¹ ) enabled detection of aerosol generation by tidal breathing (mean particle concentration 118 L ⁻¹ ). Aerosol recording during OGD showed an average particle number concentration of 595 L ⁻¹ with a wide range (3–4320 L ⁻¹ ). Bioaerosol-generating events, namely, coughing or burping, were common. Coughing was evoked in 60% of the endoscopies, with a greater peak concentration and a greater total number of sampled particles than the patient’s reference voluntary coughs (11 710 vs 2320 L ⁻¹ and 780 vs 191 particles, n=9 and p=0.008). Endoscopies with coughs generated a higher level of aerosol than tidal breathing, whereas those without coughs were not different to the background. Burps also generated increased aerosol concentration, similar to those recorded during voluntary coughs. The insertion and removal of the endoscope were not aerosol generating unless a cough was triggered.
Conclusion
Coughing evoked during OGD is the main source of the increased aerosol levels, and therefore, OGD should be regarded as a procedure with high risk of producing respiratory aerosols. OGD should be conducted with airborne personal protective equipment and appropriate precautions in those patients who are at risk of having COVID-19 or other respiratory pathogens.
The coronavirus disease 2019 (COVID-19) pandemic had caused a severe depletion of the worldwide supply of N95 respirators. The development of methods to effectively decontaminate N95 respirators while maintaining their integrity is crucial for respirator regeneration and reuse. In this study, we systematically evaluated five respirator decontamination methods using vaporized hydrogen peroxide (VHP) or ultraviolet (254 nm wavelength, UVC) radiation. Through testing the bioburden, filtration, fluid resistance, and fit (shape) of the decontaminated respirators, we found that the decontamination methods using BioQuell VHP, custom VHP container, Steris VHP, and Sterrad VHP effectively inactivated Cardiovirus (3-log10 reduction) and bacteria (6-log10 reduction) without compromising the respirator integrity after 2-15 cycles. Hope UVC system was capable of inactivating Cardiovirus (3-log10 reduction) but exhibited relatively poorer bactericidal activity. These methods are capable of decontaminating 10-1000 respirators per batch with varied decontamination times (10-200 min). Our findings show that N95 respirators treated by the previously mentioned decontamination methods are safe and effective for reuse by industry, laboratories, and hospitals.
Doğal havalandırma dolayısıyla havalandırmanın yetersiz kaldığı ülkemiz okulları sınıflarında diğer iç hava kirleticilerinin de konsantrasyonları yüksek bulunmakta ve çocuklarımız sağlık ve akademik performanslarını etkileyebilecek düzeylere maruz kalabilmektedir (Güllü, 2015; Sofuoğlu, 2015; Ekren vd., 2017). Bu tip bir sınıf ortamı, ülkemizde sınıf mevcutlarının yüksek olması (öğrenci başına düşen sınıf alanının az oluşu) ile birlikte değerlendirildiğinde, SARS-CoV-2 gibi salgına yol açan, hava yoluyla yayılabilen mikroorganizmalar için bulaşın yüksek olacağı super yayılma ortamları sunacağı ortadadır. Bu olasılığı ve çocuklarımızın iç hava kirleticilerine maruziyetini azaltmak, dolayısıyla sağlıklarını korumak ve akademik başarılarını yükseltecek bir iç çevre sunabilmek için, okullarımız sınıflarında mekanik havalandırma eklenmesi kritik önem arz etmektedir.
Background
Clinical guidelines on infection control strategies in healthcare workers (HCWs) play an important role in protecting them during the SARS-CoV-2 pandemic. Poorly constructed guidelines that are incomprehensive and/or ambiguous may compromise HCWs’ safety.
Objective
To develop and validate a tool to appraise guidelines on infection control strategies in HCWs based on the guidelines published early in the COVID-19 pandemic.
Design, Setting, and Outcomes
A three-stage, web-based, Delphi consensus-building process among a panel of diverse HCWs and healthcare managers was performed. The tool was validated by appraising 40 international, specialty-specific, and procedure-specific guidelines along with national guidelines from countries with a wide range of gross national income.
Results
Overall consensus (≥75%) was reached at the end of three rounds for all six domains included in the tool. The Delphi panel recommended an ideal infection control guideline should encompass six domains: general characteristics (domain-1), engineering recommendations (domain-2), personal protection equipment (PPE) use (domain-3), and administrative aspects (domain 4-6) of infection control. The appraisal tool performed well across the six domains and the inter-rater agreement was excellent for the 40 guidelines. All included guidelines performed relatively better in domains 1-3 compared with domains 4-6 and this was more evident in guidelines originating from lower-income countries.
Conclusion
The guideline appraisal tool was robust and easy to use. Engineering recommendations aspects of infection control, administrative measures that promote optimal PPE use, and HCW wellbeing were generally lacking in assessed guidelines. This tool may enable health systems to adopt high-quality HCW infection control guidelines during the SARS-CoV-2 pandemic and may also provide a framework for future guideline development.
The novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has created havoc worldwide ever since its emergence in December 2019. The current evidence indicates that the virus remains viable in aerosols for hours and on fomites for few days. A little information is available on the topic, the present communication reviews the perseverance and distribution of the novel coronavirus in the aerosol and on various inanimate surfaces so that the appropriate safety measures can be undertaken and the virus protection guidelines may be framed accordingly.
Environmental factors such as temperature and relative humidity can affect the inactivation and transmission of coronaviruses. By reviewing medical experiments on virus survival and virus transmission between infected and susceptible species in different temperature and humidity conditions, this study explores the influence of temperature and relative humidity on the survival and transmission of viruses, and provides suggestions, with experimental evidence, for the environmental control measures of Coronavirus Disease 2019. The results indicated that (1) virus viability and infectivity is increased at a low temperature of 5 ℃ and reduced at higher temperatures. (2) Virus survival and transmission is highly efficient in a dry environment with low relative humidity, and also in a wet environment with high relative humidity, and it is minimal at intermediate relative humidity. Therefore, in indoor environments, the lack of heating in winter or overventilation, leading to low indoor temperature, can help virus survival and help susceptible people being infected. On the contrary, modulating the indoor relative humidity at an intermediate level is conducive to curb epidemic outbreaks.
The coronavirus disease 2019 (COVID-19) pandemic has imposed a considerable burden on hospitals and healthcare workers (HCWs) worldwide, increasing the risk of outbreaks and nosocomial transmission to "non-COVID-19" patients, who represent the highest-risk population in terms of mortality, and HCWs. Since HCWs are at the interface between hospitals on the one hand and the community on the other, they are potential reservoirs, carriers, or victims of severe acute respiratory syndrome coronavirus 2 cross-transmission. In addition, there has been a paradigm shift in the management of viral respiratory outbreaks, such as the widespread testing of patients and HCWs, including asymptomatic individuals. In hospitals, there is a risk of aerosol transmission in poorly ventilated spaces, and when performing aerosol-producing procedures, it is imperative to take measures against aerosol transmission. In particular, spatial separation of the inpatient ward for non-COVID-19 patients from that designated for patients with suspected or confirmed COVID-19 as well as negative-pressure isolation on the floor of the ward, using an airborne infection isolation device could help prevent nosocomial infection.
Scientists across disciplines, policymakers, and journalists have voiced frustration at the unprecedented polarization and misinformation around coronavirus disease 2019 (COVID-19) pandemic. Several false dichotomies have been used to polarize debates while oversimplifying complex issues. In this comprehensive narrative review, we deconstruct six common COVID-19 false dichotomies, address the evidence on these topics, identify insights relevant to effective pandemic responses, and highlight knowledge gaps and uncertainties. The topics of this review are: 1) Health and lives vs. economy and livelihoods, 2) Indefinite lockdown vs. unlimited reopening, 3) Symptomatic vs. asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, 4) Droplet vs. aerosol transmission of SARS-CoV-2, 5) Masks for all vs. no masking, and 6) SARS-CoV-2 reinfection vs. no reinfection. We discuss the importance of multidisciplinary integration (health, social, and physical sciences), multilayered approaches to reducing risk (“Emmentaler cheese model”), harm reduction, smart masking, relaxation of interventions, and context-sensitive policymaking for COVID-19 response plans. We also address the challenges in understanding the broad clinical presentation of COVID-19, SARS-CoV-2 transmission, and SARS-CoV-2 reinfection. These key issues of science and public health policy have been presented as false dichotomies during the pandemic. However, they are hardly binary, simple, or uniform, and therefore should not be framed as polar extremes. We urge a nuanced understanding of the science and caution against black-or-white messaging, all-or-nothing guidance, and one-size-fits-all approaches. There is a need for meaningful public health communication and science-informed policies that recognize shades of gray, uncertainties, local context, and social determinants of health.
Front-line staff routinely exposed to aerosol-generating procedures are at a particularly high risk of transmission of severe acute respiratory syndrome coronavirus 2. We aimed to assess the adequacy of respiratory protection provided by available N95/P2 masks to staff routinely exposed to aerosol-generating procedures. We performed a prospective audit of fit-testing results. A convenience sample of staff from the Department of Anaesthesia and Pain Medicine, who opted to undergo qualitative and/or quantitative fit-testing of N95/P2 masks was included. Fit-testing was performed following standard guidelines including a fit-check. We recorded the type and size of mask, pass or failure and duration of fit-testing. Staff completed a short questionnaire on previous N95/P2 mask training regarding confidence and knowledge gained through fit-testing. The first fit-pass rate using routinely available N95/P2 masks at this institution was only 47%. Fit-pass rates increased by testing different types and sizes of masks. Confidence ‘that the available mask will provide adequate fit’ was higher after fit-testing compared with before fit-testing; (median, interquartile range) five-point Likert-scale (4.0 (4.0–5.0) versus 3.0 (2.0–4.0); P<0.001). This audit highlights that without fit-testing over 50% of healthcare workers were using an N95/P2 mask that provided insufficient airborne protection. This high unnoticed prevalence of unfit masks among healthcare workers can create a potentially hazardous false sense of security. However, fit-testing of different masks not only improved airborne protection provided to healthcare workers but also increased their confidence around mask protection.
Global shortages of personal protective equipment (PPE) have been at the forefront of public attention throughout the recent crisis. Initial lack of information regarding the route of transmission of the virus fuelled panic buying of face masks and gloves, as well as shortages in healthcare facilities. Home-made cloth masks have become commonplace, and makers have seized upon opportunities to increase capacity by producing PPE with 3D printing. Mask designs typically incorporate flexible filament face pieces with an integrated filter, but devices to improve the fit of simple surgical face masks have also been produced, and are not burdened with such strict testing requirements. Manufacture of face shields has been a triumph for the 3D printing community, with the availability of highly optimised and tested designs which are printable on most domestic machines, comfortable to use, and keep production time to a minimum. Across the globe, these devices have been manufactured locally and delivered to nearby hospitals by volunteers. Thus, the COVID-19 pandemic has spurred development in the field of distributed manufacturing, the long-awaited holy grail of home 3D printing. In the following chapter, we provide an overview of currently available 3D printed PPE, reviewing the designs for durability, ease of use, and clinical effectiveness, as well as exploring future directions for PPE manufacture by 3D printing.
This paper presents a method of implementation and the results of aerosol dispersion tests in underground mine workings. Numerous tests were carried out to determine the potential risk of SARS-CoV-2 coronavirus infection in the underground environment of the mines. The influence of selected parameters of mine air on the possibility and method of aerosol transmission through ventilation routes was experimentally determined in real conditions. The concentration of additional aerosols in the class of ultrafine and fine aerosols increased with the distance from the generator, while the concentration of coarse particles decreased. Assuming the consumption of the solution with which aerosols were generated, even at a small level of 1 cm3/min., the number of additional aerosols was several hundred particles in one cubic centimeter of air at a distance of 50–70 m from the generator. The concentration of ultrafine particles in the range of 40–20,000 nm increased from 122 particles/cm3 to 209 particles/cm3 at air temperature of 12 °C and relative humidity of 95–96%, and from 90 particles/cm3 to 243 particles/cm3 at air temperature of 17 °C and relative humidity of 76–82%, with the increasing distance from the generator (10 m to 50 m).
During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a regular 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 airborne route is likely. It is vital to identify features of cases such as this so as to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was by
inhalation of respiratory aerosol, we use the available evidence to infer the emission rate of airborne infectious quanta from the primary source. We also explore how the risk of infection would vary with several influential factors: the rates of removal of respiratory aerosol by ventilation; deposition onto surfaces; and viral decay. The results indicate an emission rate of the order of a thousand quanta per hour (mean [interquartile range] for this event = 970 [680-1190] quanta per hour) and demonstrate that the risk of infection is modulated by ventilation conditions, occupant density, and duration of shared presence with an infectious individual.
Airborne transmission is a recognized pathway of contagion; however, it is rarely quantitatively evaluated. This study presents a novel approach for quantitative assessment of the individual infection risk of susceptible subjects exposed in indoor microenvironments in the presence of an asymptomatic infected SARS-CoV-2 subject. The approach allowed the maximum risk for an exposed healthy subject to be evaluated or, starting from an acceptable risk, the maximum exposure time. We applied the proposed approach to four distinct scenarios for a prospective assessment, highlighting that, in order to guarantee an acceptable individual risk of 10 ⁻³ for exposed subjects in naturally ventilated indoor environments, the exposure time should be shorter than 20 min. The proposed approach was used for retrospective assessment of documented outbreaks in a restaurant in Guangzhou (China) and at a choir rehearsal in Mount Vernon (USA), showing that, in both cases, the high attack rate values can be justified only assuming the airborne transmission as the main route of contagion. Moreover, we shown that such outbreaks are not caused by the rare presence of a superspreader, but can be likely explained by the co-existence of conditions, including emission and exposure parameters, leading to a highly probable event, which can be defined as a superspreading event.
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.
To determine possible modes of virus transmission, we investigated a cluster of COVID-19 cases associated with a shopping mall in Wenzhou, China. Data indicated that indirect transmission of the causative virus occurred, perhaps resulting from virus contamination of common objects, virus aerosolization in a confined space, or spread from asymptomatic infected persons.
Little is known about the amount and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-minute breath samples (coarse >5-µm and fine ≤5-µm fractions) on days 1-3 after symptom onset. We assessed viral RNA copy number for all samples and cultured NP swabs and fine aerosols. We recovered infectious virus from 52 (39%) of the fine aerosols and 150 (89%) of the NP swabs with valid cultures. The geometric mean RNA copy numbers were 3.8 × 104/30-minutes fine-, 1.2 × 104/30-minutes coarse-aerosol sample, and 8.2 × 108 per NP swab. Fine- and coarse-aerosol viral RNA were positively associated with body mass index and number of coughs and negatively associated with increasing days since symptom onset in adjusted models. Fine-aerosol viral RNA was also positively associated with having influenza vaccination for both the current and prior season. NP swab viral RNA was positively associated with upper respiratory symptoms and negatively associated with age but was not significantly associated with fine- or coarse-aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent.
Rationale:
Respiratory syncytial virus (RSV) is a highly contagious pathogen with a huge global health impact. It is a major cause of hospital acquired infection with large numbers of those exposed developing infection. Those infected in hospital are at increased risk of a severe clinical course. Prevention of nosocomial spread currently focuses on spread by hand and large droplets. There is little research evidence to determine if aerosol spread of infectious RSV by aerosol is possible Objectives: To determine infants with RSV positive bronchiolitis produce aerosolized particles containing RSV that remains capable of causing infection.
Methods:
The amount of RSV contained in aerosolized particles was measured using viable impactor sampling produced by infants with bronchiolitis due to RSV. The ability of RSV contained in these particles to infected human ciliated respiratory epithelium was determined.
Results:
We show for the first time that infants with RSV positive bronchiolitis nursed in a ward setting or ventilated in intensive care produce large numbers of aerosol particles containing RSV that remained infectious, capable of infecting human ciliated epithelium. A significant amount of RSV was found in particles with aerodynamic diameters less than five microns.
Conclusions:
Many of the aerosolized particles, containing RSV, generated by infants with bronchiolitis were sufficiently small to remain airborne for a significant length of time and small enough to be inhaled and deposited throughout the respiratory tract. It is likely that this leads to spread of infection to others with dissemination of infection throughout the respiratory tract.
Patients with influenza release aerosol particles containing the virus into their environment. However, the importance of airborne transmission in the spread of influenza is unclear, in part because of a lack of information about the infectivity of the airborne virus. The purpose of this study was to determine the amount of viable influenza A virus that was expelled by patients in aerosol particles while coughing. Sixty-four symptomatic adult volunteer outpatients were asked to cough 6 times into a cough aerosol collection system. Seventeen of these participants tested positive for influenza A virus by viral plaque assay (VPA) with confirmation by viral replication assay (VRA). Viable influenza A virus was detected in the cough aerosol particles from 7 of these 17 test subjects (41%). Viable influenza A virus was found in the smallest particle size fraction (0.3 µm to 8 µm), with a mean of 142 plaque-forming units (SD 215) expelled during the 6 coughs in particles of this size. These results suggest that a significant proportion of patients with influenza A release small airborne particles containing viable virus into the environment. Although the amounts of influenza A detected in cough aerosol particles during our experiments were relatively low, larger quantities could be expelled by influenza patients during a pandemic when illnesses would be more severe. Our findings support the idea that airborne infectious particles could play an important role in the spread of influenza.
There is uncertainty about the mode of transmission of the severe acute respiratory syndrome (SARS) virus. We analyzed the temporal and spatial distributions of cases in a large community outbreak of SARS in Hong Kong and examined the correlation of these data with the three-dimensional spread of a virus-laden aerosol plume that was modeled using studies of airflow dynamics.
We determined the distribution of the initial 187 cases of SARS in the Amoy Gardens housing complex in 2003 according to the date of onset and location of residence. We then studied the association between the location (building, floor, and direction the apartment unit faced) and the probability of infection using logistic regression. The spread of the airborne, virus-laden aerosols generated by the index patient was modeled with the use of airflow-dynamics studies, including studies performed with the use of computational fluid-dynamics and multizone modeling.
The curves of the epidemic suggested a common source of the outbreak. All but 5 patients lived in seven buildings (A to G), and the index patient and more than half the other patients with SARS (99 patients) lived in building E. Residents of the floors at the middle and upper levels in building E were at a significantly higher risk than residents on lower floors; this finding is consistent with a rising plume of contaminated warm air in the air shaft generated from a middle-level apartment unit. The risks for the different units matched the virus concentrations predicted with the use of multizone modeling. The distribution of risk in buildings B, C, and D corresponded well with the three-dimensional spread of virus-laden aerosols predicted with the use of computational fluid-dynamics modeling.
Airborne spread of the virus appears to explain this large community outbreak of SARS, and future efforts at prevention and control must take into consideration the potential for airborne spread of this virus.
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.
The transmission of some infectious diseases requires that pathogens can survive (i.e., remain infectious) in the environment, outside the host. Relative humidity (RH) is known to affect the survival of some microorganisms in the environment; however, the mechanism underlying the relationship has not been explained, particularly for viruses. We investigated the effects of RH on the viability of bacteria and viruses in both suspended aerosols and stationary droplets using traditional culture-based approaches. Results showed that viability of bacteria generally decreased with decreasing RH. Viruses survived well at RHs lower than 33% and at 100%, whereas their viability was reduced at intermediate RHs. We then explored the evaporation rate of droplets consisting of culture media and the resulting changes in solute concentrations over time; as water evaporates from the droplets, solutes such as sodium chloride in the media become more concentrated. Based on the results, we suggest that inactivation of bacteria is influenced by osmotic pressure resulting from elevated concentration of salts as droplets evaporate. We propose that the inactivation of viruses is governed by the cumulative dose of solutes, or the product of concentration and time, as in disinfection kinetics. These findings emphasize that evaporation kinetics play a role in modulating the survival of microorganisms in droplets.
Background:
The largest outbreak of Middle East respiratory syndrome (MERS) outside the Middle East occurred in South Korea in 2015 and resulted in 186 laboratory-confirmed infections, including 36 (19%) deaths. Some hospitals were considered epicenters of infection and voluntarily shut down most of their operations after nearly half of all transmissions occurred in hospital settings. However, the ways that MERS-coronavirus (MERS-CoV) is transmitted in healthcare settings are not well defined.
Methods:
We explored the possible contribution of contaminated hospital air and surfaces to MERS transmission by collecting air and swabbing environmental surfaces in two hospitals treating MERS-CoV patients. The samples were tested by viral culture with reverse-transcriptase polymerase chain reaction (RT-PCR) and immunofluorescence assay (IFA) using MERS-CoV Spike antibody, and electron microscopy (EM).
Results:
The presence of MERS-CoV was confirmed by RT-PCR of viral cultures of four out of seven air samples from two patients' rooms, one patient's restroom, and one common corridor. In addition, MERS-CoV was detected in 15 of 68 surface swabs by viral cultures. IFA on the cultures of the air and swab samples revealed the presence of MERS-CoV. EM images also revealed intact particles of MERS-CoV in viral cultures of the air and swab samples.
Conclusions:
These data provide experimental evidence for extensive viable MERS-CoV contamination of the air and surrounding materials in MERS outbreak units. Thus our findings call for epidemiologic investigation of the possible scenarios for contact and airborne transmission, and raise concern regarding the adequacy of current infection control procedures.
Very low air velocities were measured in six occupied homes and one unoccupied house particularly when forced-air air-conditioning systems (i.e., HVAC) were turned off. Segregating the velocity data by monitoring site, median velocities of 4.2, 4.3, 10.2, and 12.4 cm/s were found in the master bedroom, basement, and kitchen of the six occupied homes and the dining/living room of the unoccupied house, respectively. In the occupied homes, the comparatively high velocities in the kitchens correlated with increased occupant activities and the use of ceiling and/or exhaust fans. Segregating the data by use of forced-air HVAC systems, the median velocities increased from 5.8 to 6.2, 3.2 to 5.7, 1.5 to 8.1, and 4.4 to 15.5. cm/s with HVAC operation in three occupied houses and one unoccupied house, respectively. The lowest median velocity of 1.1 cm/s was found in a parent's bedroom, where occupant activities were purposely limited and the HVAC was off. These low air velocities raise concern that air movement may sometimes be inadequate for quantitative passive monitoring of pollutant vapors. Ten and 50% reductions in sampling rates are reported in the literature for passive monitors at air velocities ranging from <0.7 to 25 cm/s and from <0.7 to 2 cm/s, respectively. In addition, low velocities may limit off-gassing from evaporatively controlled emitters and decrease the thermal comfort of inhabitants under warm and humid conditions.
A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm−3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm−3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm−3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm−3 for breathing to 1.1 cm−3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.
Abstract
Abstract A large number of infectious diseases are believed to be transmitted between people via large droplets and by airborne routes. An understanding of evaporation and dispersion of droplets and droplet nuclei is not only significant for developing effective engineering control methods for infectious diseases but also for exploring the basic transmission mechanisms of the infectious diseases. How far droplets can move is related to how far droplet-borne diseases can transmit. A simple physical model is developed and used here to investigate the evaporation and movement of droplets expelled during respiratory activities; in particular, the well-known Wells evaporation–falling curve of droplets is revisited considering the effect of relative humidity, air speed, and respiratory jets. Our simple model considers the movement of exhaled air, as well as the evaporation and movement of a single droplet. Exhaled air is treated as a steady-state non-isothermal (warm) jet horizontally issuing into stagnant surrounding air. A droplet is assumed to evaporate and move in this non-isothermal jet. Calculations are performed for both pure water droplets and droplets of sodium chloride (physiological saline) solution (0.9% w/v). We calculate the droplet lifetimes and how droplet size changes, as well as how far the droplets travel in different relative humidities. Our results indicate that a droplet's size predominately dictates its evaporation and movement after being expelled. The sizes of the largest droplets that would totally evaporate before falling 2 m away are determined under different conditions. The maximum horizontal distances that droplets can reach during different respiratory activities are also obtained. Our study is useful for developing effective prevention measures for controlling infectious diseases in hospitals and in the community at large.
Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant
- Li
Li, Y. et al. Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated
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Evidence of respiratory syncytial virus spread by aerosol
- H Kulkarni
Kulkarni, H. et al. Evidence of respiratory syncytial virus spread by aerosol. Time to revisit infection
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Quantitative assessment of the risk of airborne transmission of SARS-CoV-2 infection: perspective and retrospective applications
- Buonanno
Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant
- Y Li
- H Qian
- J Hang
Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event
- SL Miller
- WW Nazaroff
- JL Jimenez
Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event
- Miller
Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals
- Liu