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

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

Aerosol transmission,an indispensable route of COVID-19 spread:case study of a department-store cluster

Patients with COVID-19 have revealed a massive outbreak around the world,leading to widespread concerns in global scope.Figuring out the transmission route of COVID-19 is necessary to control further spread.We analyzed the data of 43 patients in Baodi Department Store(China)to supplement the transmission route and epidemiological characteristics of COVID-19 in a cluster outbreak.Incubation median was estimated to endure 5.95 days(2-13 days).Almost 76.3%of patients sought medical attention immediately upon illness onset.The median period of illness onset to hospitalization and confirmation were 3.96 days(0-14)and 5.58 days(1-21),respectively.Patients with different cluster case could demonstrate unique epidemiological characteristics due to the particularity of outbreak sites.SRAS-CoV-2 can be released into the surrounding air through patient's respiratory tract activities,and can exist for a long time for long-distance transportation.SRAS-CoV-2 RNA can be detected in aerosol in different sites,including isolation ward,general ward,outdoor,toilet,hallway,and crowded public area.Environmental factors influencing were analyzed and indicated that the SARS-CoV-2 transportation in aerosol was dependent on temperature,air humidity,ventilation rate and inactivating chemicals(ozone)content.As for the infection route of case numbers 2 to 6,10,13,16,17,18,20 and 23,we believe that aerosol transmission played a significant role in analyzing their exposure history and environmental conditions in Baodi Department Store.Aerosol transmission could occur in some cluster cases when the environmental factors are suitable,and it is an indispensable route of COVID-19 spread.

SARS-CoV-2 aerosol transmission and detection

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

Potential effects of aerosol generation and transmission during bedside endoscope cleaning

Airborne transmission is among the most frequent types of nosocomial infection.Recent years have witnessed frequent outbreaks of airborne diseases,such as severe acute respiratory syndrome(SARS)in 2002,Middle East respiratory syndrome(MERS)in 2012,and coronavirus disease 2019(COVID-19),with the latter being on the rampage since the end of 2019 and bringing the effect of aerosols on health back to the fore(Gralton et al.,2011;Wang et al.,2021).An increasing number of studies have shown that certain highly transmissible pathogens can maintain long-term stability and efficiently spread through aerosols(Leung,2021;Lv et al.,2021).As reported previously,influenza viruses that can spread efficiently through aerosols remain stable for a longer period compared to those that cannot.The World Health Organization(WHO)has stated that aerosol-generating procedures(AGPs)play an important role in aerosol transmission in hospitals(Calderwood et al.,2021).AGPs,referring to medical procedures that produce aerosols,including dental procedures,endotracheal intubation,sputum aspiration,and laparoscopic surgeries,have been reported to be significantly associated with an increased risk of nosocomial infection among medical personnel(Hamilton,2021).

Research progress of severe acute respiratory syndrome coronavirus 2 on aerosol collection and detection

The outbreak of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)in late 2019 has negatively affected people's lives and productivity.Because the mode of transmission of SARS-CoV-2 is of great concern,this review discusses the sources of virus aerosols and possible transmission routes.First,we discuss virus aerosol collection methods,including natural sedimentation,solid impact,liquid impact,centrifugal,cyclone and electrostatic adsorption methods.Then,we review common virus aerosol detection methods,including virus culture,metabolic detection,nucleic acid-based detection and immunology-based detection methods.Finally,possible solutions for the detection of SARS-CoV-2 aerosols are introduced.Point-of-care testing has long been a focus of attention.In the near future,the development of an instrument that integrates sampling and output results will enable the real-time,automatic monitoring of patients.

Influence of indoor airflow on airborne disease transmission in a classroom

It has been widely accepted that the most effective way to mitigate airborne disease transmission in an indoor space is to increase the ventilation airflow,measured in air change per hour(ACH).However,increasing ACH did not effectively prevent the spread of COVID-19.To better understand the role of ACH and airflow large-scale patterns,a comprehensive fully transient computational fluid dynamics(CFD)simulation of two-phase flows based on a discrete phase model(DPM)was performed in a university classroom setting with people present.The investigations encompass various particle sizes,ventilation layouts,and flow rates.The findings demonstrated that the particle size threshold at which particles are deemed airborne is highly influenced by the background flow strength and large-scale flow pattern,ranging from 5µm to 10µm in the cases investigated.The effects of occupants are significant and must be precisely accounted for in respiratory particle transport studies.An enhanced ventilation design(UFAD-CDR)for university classrooms is introduced that places a premium on mitigating airborne disease spread.Compared to the baseline design at the same ACH,this design successfully reduced the maximum number density of respiratory particles by up to 85%.A novel airflow-related parameter,Horizontality,is introduced to quantify and connect the large-scale airflow pattern with indoor aerosol transport.This underscores that ACH alone cannot ensure or regulate air quality.In addition to the necessary ACH for air exchange,minimizing horizontal bulk motion is essential for reducing aerosol transmissibility within the room.

An overview for monitoring and prediction of pathogenic microorganisms in the atmosphere

Corona virus disease 2019(COVID-19)has exerted a profound adverse impact on human health.Studies have demonstrated that aerosol transmission is one of the major transmission routes of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).Pathogenic microorganisms such as SARS-CoV-2 can survive in the air and cause widespread infection among people.Early monitoring of pathogenic microorganism transmission in the atmosphere and accurate epidemic prediction are the frontier guarantee for preventing large-scale epidemic outbreaks.Monitoring of pathogenic microorganisms in the air,especially in densely populated areas,may raise the possibility to detect viruses before people are widely infected and contain the epidemic at an earlier stage.The multi-scale coupled accurate epidemic prediction system can provide support for governments to analyze the epidemic situation,allocate health resources,and formulate epidemic response policies.This review first elaborates on the effects of the atmospheric environment on pathogenic microorganism transmission,which lays a theoretical foundation for the monitoring and prediction of epidemic development.Secondly,the monitoring technique development and the necessity of monitoring pathogenic microorganisms in the atmosphere are summarized and emphasized.Subsequently,this review introduces the major epidemic prediction methods and highlights the significance to realize a multi-scale coupled epidemic prediction system by strengthening the multidisciplinary cooperation of epidemiology,atmospheric sciences,environmental sciences,sociology,demography,etc.By summarizing the achievements and challenges in monitoring and prediction of pathogenic microorganism transmission in the atmosphere,this review proposes suggestions for epidemic response,namely,the establishment of an integrated monitoring and prediction platform for pathogenic microorganism transmission in the atmosphere.

Control of exhaled SARS-CoV-2-laden aerosols in the interpersonal breathing microenvironment in a ventilated room with limited space air stability

The Coronavirus Disease 2019(COVID-19)highlights the importance of understanding and controlling the spread of the coronavirus between persons.We experimentally and numerically investigated an advanced engineering and environmental method on controlling the transmission of airborne SARS-CoV-2-laden aerosols in the breathing microenvironment between two persons during interactive breathing process by combining the limited space air stability and a ventilation method.Experiments were carried out in a full-scale ventilated room with different limited space air stability conditions,i.e.,stable condition,neutral condition and unstable condition.Two real humans were involved to conducted normal breathing process in the room and the exhaled carbon dioxide was used as the surrogate of infectious airborne SARS-CoV-2-laden aerosols from respiratory activities.A correspondent numerical model was established to visualize the temperature field and contaminated field in the test room.Results show that the performance of a ventilation system on removing infectious airborne SARS-CoV-2-laden aerosols from the interpersonal breathing microenvironment is dependent on the limited space air stability conditions.Appropriate ventilation method should be implemented based on an evaluation of the air condition.It is recommended that total volume ventilation methods are suitable for unstable and neutral conditions and local ventilation methods are preferable for stable conditions.This study provides an insight into the transmission of airborne SARS-CoV-2-laden aerosols between persons in ventilated rooms with different limited space air stability conditions.Useful guidance has been provided to cope with COVID-19 in limited spaces.