Mechanistic insights into the effect of humidity on airborne influenza virus survival, transmission and incidence

Inhaled aerosols: Their role in COVID-19 transmission, including biophysical interactions in the lungs

The high rate of spreading of COVID-19 is attributed to airborne particles exhaled by infected but often asymptomatic individuals. In this review, the role of aerosols in SARS-CoV-2 coronavirus transmission is discussed from the biophysical perspective. The essential properties of the coronavirus virus transported inside aerosol droplets, their successive inhalation, and size-dependent deposition in the respiratory system are highlighted. The importance of face covers (respirators and masks) in the reduction of aerosol spreading is analyzed. Finally, the discussion of the physicochemical phenomena of the coronavirus entering the surface of lung liquids (bronchial mucus and pulmonary surfactant) is presented with a focus on a possible role of interfacial phenomena in pulmonary alveoli. Information given in this review should be important in understanding the essential biophysical conditions of COVID-19 infection via aerosol route as a prerequisite for effective strategies of respiratory tract protection, and possibly, indications for future treatments of the disease.

Community Use of Face Masks against the Spread of COVID-19

The role of face masks to prevent and control COVID-19 is critical, especially since asymptomatic or pre-symptomatic infected individuals can shed high loads of SARS-CoV-2 in the surrounding environment. In addition to being a two-way barrier to protect against virions droplets both in terms of "source control" (for the benefits of the community) and "physical protection" (for wearer), face masks also allow maintaining physiological temperatures and humidity of the nasal cavity and mouth, independently from the external environmental conditions. Beyond compromising the viral transmission speed, exposure to cold environments could have a detrimental effect on the host's susceptibility to SARS-CoV-2. The innate human immune system becomes in fact weaker with cooler nose temperatures and thus more vulnerable to viral replication. Furthermore, there is evidence that warm, humid climates are associated with reduced spread of SARS-CoV-2, while cold dry conditions favor its stability and transmissibility. In the early stage of a viral infection, a physiological body temperature in the upper airways supports the innate immune system, endorsing the muco-ciliary clearance, inhibiting, or deactivating any first settlement of viruses. Face masks are therefore strongly recommended also outdoors, especially under cold weather conditions, not only as a physical barrier against the transmission of SARS-CoV-2, but also to prevent the rapid cooling of the nasal mucosa and the inhibition of the human innate defense of the upper airways.

Wildland firefighter exposure to smoke and COVID-19: A new risk on the fire line

Throughout the United States, wildland firefighters respond to wildfires, performing arduous work in remote locations. Wildfire incidents can be an ideal environment for the transmission of infectious diseases, particularly for wildland firefighters who congregate in work and living settings. In this review, we examine how exposure to wildfire smoke can contribute to an increased likelihood of SARS-CoV-2 infection and severity of coronavirus disease (COVID-19). Human exposure to particulate matter (PM), a component of wildfire smoke, has been associated with oxidative stress and inflammatory responses; increasing the likelihood for adverse respiratory symptomology and pathology. In multiple epidemiological studies, wildfire smoke exposure has been associated with acute lower respiratory infections, such as bronchitis and pneumonia. Co-occurrence of SARS-CoV-2 infection and wildfire smoke inhalation may present an increased risk for COVID-19 illness in wildland firefighters due to PM based transport of SARS CoV-2 virus and up-regulation of angiotensin-converting enzyme II (ACE-2) (i.e. ACE-2 functions as a trans-membrane receptor, allowing the SARS-CoV-2 virus to gain entry into the epithelial cell). Wildfire smoke exposure may also increase risk for more severe COVID-19 illness such as cytokine release syndrome, hypotension, and acute respiratory distress syndrome (ARDS). Current infection control measures, including social distancing, wearing cloth masks, frequent cleaning and disinfecting of surfaces, frequent hand washing, and daily screening for COVID-19 symptoms are very important measures to reduce infections and severe health outcomes. Exposure to wildfire smoke may introduce additive or even multiplicative risk for SARS-CoV-2 infection and severity of disease in wildland firefighters. Thus, additional mitigative measures may be needed to prevent the co-occurrence of wildfire smoke exposure and SARS-CoV-2 infection.

The SARS-COV-2 outbreak around the Amazon rainforest: The relevance of the airborne transmission

At the beginning of the SARS-COV-2 outbreak in Brazil, there was a striking difference between the contamination rate in the Amazonian States and the South and the Southeast States. The regions near the Amazon rainforest presented much higher and faster contaminations. This paper attempts to explain this phenomenon through a global analysis of the COVID-19 epidemic in Brazil. It also investigates the relationship between climate conditions and airborne transmission with the evolution of contagion in the Amazonian states. The method of investigation of the spread of SARS-COV-2 in these different macro-environments was based on the analysis of three extensive daily official databases on the number of deaths, the percentage of adherence of the populations to the restriction policies, and the local climatic conditions. Besides, the social conditions in those States were also taken into account. Then, it was compared the epidemiologic results for States with very different climatic characteristics and that had adopted, almost simultaneously, similar social isolation measures. However, all these analyses were not able to explain the remarkable difference in the evolution of the pandemic among Brazilian regions. So, it was necessary to invoke airborne transmission, facilitated by the very high air humidity, as a decisive factor to explain the faster evolution of contagion in the rainforest region. Air humidity seems to be the most important climatic factor in viral spreading, while usual ambient temperatures do not have a strong influence. Another very important result of this analysis was the observation that the onset of collective immunity may have been achieved with a contamination rate of about 15% of the Amazonian population.

Indoor Environmental Factors and Acute Respiratory Illness in a Prospective Cohort of Community-Dwelling Older Adults

BACKGROUND

Ambient environmental factors have been associated with respiratory infections in ecological studies, but few studies have explored the impact of indoor environmental factors in detail. The current study aimed to investigate the impact of indoor environment on the risk of acute respiratory illness (ARI) in a subtropical city.

METHOD

A prospective cohort study was conducted in 285 community-dwelling older adults from December 2016 through May 2019. Individual household indoor environment data and ARI incidence were continuously collected. A time-stratified case-crossover analysis was conducted to estimate the excess risk of ARI associated with per-unit increase of daily mean indoor temperature, relative humidity, and absolute humidity (AH).

RESULT

In total, 168 episodes of ARI were reported with an average risk of 36.8% per year. We observed a negative association of ARI with indoor AH up to 5 lag days in cool seasons, with a 6-day cumulative excess risk estimate of -9.0% (95% confidence interval, -15.9% to -1.5%). Negative associations between household temperature or relative humidity and ARI were less consistent across warm and cool seasons.

CONCLUSIONS

Lower indoor AH in household was associated with a higher risk of ARI in the community-dwelling older adults in Hong Kong during cold seasons.

A psychrometric model to assess the biological decay of the SARS-CoV-2 virus in aerosols

There is increasing evidence that the 2020 COVID-19 pandemic has been influenced by variations in air temperature and humidity. However, the impact that these environmental parameters have on survival of the SARS-CoV-2 virus has not been fully characterised. Therefore, an analytical study was undertaken using published data to develop a psychrometric model to assess the biological decay rate of the virus in aerosols. This revealed that it is possible to describe with reasonable accuracy (R 2 = 0.718, p < 0.001) the biological decay constant for the SARS-CoV-2 virus using a regression model with enthalpy, vapour pressure and specific volume as predictors. Applying this to historical meteorological data from London, Paris and Milan over the pandemic period, produced results which indicate that the average half-life of the virus in aerosols outdoors was in the region 13-22 times longer in March 2020, when the outbreak was accelerating, than it was in August 2020 when epidemic in Europe was at its nadir. However, indoors, this variation is likely to be much less. As such, this suggests that changes in virus survivability due the variations in the psychrometric qualities of the air might influence the transmission of SARS-CoV-2.

The Relationship Between the Global Burden of Influenza From 2017 to 2019 and COVID-19: Descriptive Epidemiological Assessment

BACKGROUND

SARS-CoV-2 and influenza are lipid-enveloped viruses with differential morbidity and mortality but shared modes of transmission.

OBJECTIVE

With a descriptive epidemiological framing, we assessed whether recent historical patterns of regional influenza burden are reflected in the observed heterogeneity in COVID-19 cases across regions of the world.

METHODS

Weekly surveillance data reported by the World Health Organization from January 2017 to December 2019 for influenza and from January 1, 2020 through October 31, 2020, for COVID-19 were used to assess seasonal and temporal trends for influenza and COVID-19 cases across the seven World Bank regions.

RESULTS

In regions with more pronounced influenza seasonality, COVID-19 epidemics have largely followed trends similar to those seen for influenza from 2017 to 2019. COVID-19 epidemics in countries across Europe, Central Asia, and North America have been marked by a first peak during the spring, followed by significant reductions in COVID-19 cases in the summer months and a second wave in the fall. In Latin America and the Caribbean, COVID-19 epidemics in several countries peaked in the summer, corresponding to months with the highest influenza activity in the region. Countries from regions with less pronounced influenza activity, including South Asia and sub-Saharan Africa, showed more heterogeneity in COVID-19 epidemics seen to date. However, similarities in COVID-19 and influenza trends were evident within select countries irrespective of region.

CONCLUSIONS

Ecological consistency in COVID-19 trends seen to date with influenza trends suggests the potential for shared individual, structural, and environmental determinants of transmission. Using a descriptive epidemiological framework to assess shared regional trends for rapidly emerging respiratory pathogens with better studied respiratory infections may provide further insights into the differential impacts of nonpharmacologic interventions and intersections with environmental conditions. Ultimately, forecasting trends and informing interventions for novel respiratory pathogens like COVID-19 should leverage epidemiologic patterns in the relative burden of past respiratory pathogens as prior information.

Viruses such as SARS-CoV-2 can be partially shielded from UV radiation when in particles generated by sneezing or coughing: Numerical simulations

UV radiation can inactivate viruses such as SARS-CoV-2. However, designing effective UV germicidal irradiation (UVGI) systems can be difficult because the effects of dried respiratory droplets and other fomites on UV light intensities are poorly understood. Numerical modeling of UV intensities inside virus-containing particles on surfaces can increase understanding of these possible reductions in UV intensity. We model UV intensities within spherical approximations of virions randomly positioned within spherical particles. The model virions and dried particles have sizes and optical properties to approximate SARS-CoV-2 and dried particles formed from respiratory droplets, respectively. In 1-, 5- and 9-µm diameter particles on a surface, illuminated by 260-nm UV light from a direction perpendicular to the surface, 0%, 10% and 18% (respectively) of simulated virions are exposed to intensities less than 1/100th of intensities in individually exposed virions (i.e., they are partially shielded). Even for 302-nm light (simulating sunlight), where absorption is small, 0% and 11% of virions in 1- and 9-µm particles have exposures 1/100th those of individually exposed virions. Shielding is small to negligible in sub-micron particles. Results show that shielding of virions in a particle can be reduced by illuminating a particle either from multiple widely separated incident directions, or by illuminating a particle rotating in air for a time sufficient to rotate through enough orientations. Because highly UV-reflective paints and surfaces can increase the angular ranges of illumination and the intensities within particles, they appear likely to be useful for reducing shielding of virions embedded within particles.

Seasonal association between viral causes of hospitalised acute lower respiratory infections and meteorological factors in China: a retrospective study

BACKGROUND

Acute lower respiratory infections (ALRIs) caused by respiratory viruses are common and persistent infectious diseases worldwide and in China, which have pronounced seasonal patterns. Meteorological factors have important roles in the seasonality of some major viruses, especially respiratory syncytial virus (RSV) and influenza virus. Our aim was to identify the dominant meteorological factors and to model their effects on common respiratory viruses in different regions of China.

METHODS

We analysed monthly virus data on patients hospitalised with ALRI from 81 sentinel hospitals in 22 provinces in mainland China from Jan 1, 2009, to Sept 30, 2013. We considered seven common respiratory viruses: RSV, influenza virus, human parainfluenza virus, adenovirus, human metapneumovirus, human bocavirus, and human coronavirus. Meteorological data of the same period were used to analyse relationships between virus seasonality and seven meteorological factors according to region (southern vs northern China). The geographical detector method was used to quantify the explanatory power of each meteorological factor, individually and interacting in pairs, on the respiratory viruses.

FINDINGS

28 369 hospitalised patients with ALRI were tested, 10 387 (36·6%) of whom were positive for at least one virus, including RSV (4091 [32·0%] patients), influenza virus (2665 [20·8%]), human parainfluenza virus (2185 [17·1%]), adenovirus (1478 [11·6%]), human bocavirus (1120 [8·8%]), human coronavirus (637 [5·0%]), and human metapneumovirus (615 [4·8%]). RSV and influenza virus had annual peaks in the north and biannual peaks in the south. Human parainfluenza virus and human bocavirus had higher positive rates in the spring-summer months. Human metapneumovirus had an annual peak in winter-spring, especially in the north. Adenovirus and human coronavirus exhibited no clear annual seasonality. Temperature, atmospheric pressure, vapour pressure, and rainfall had most explanatory power on most respiratory viruses in each region. Relative humidity was only dominant in the north, but had no significant explanatory power for most viruses in the south. Hours of sunlight had significant explanatory power for RSV and influenza virus in the north, and for most viruses in the south. Wind speed was the only factor with significant explanatory power for human coronavirus in the south. For all viruses, interactions between any two of the paired factors resulted in enhanced explanatory power, either bivariately or non-linearly.

INTERPRETATION

Spatiotemporal heterogeneity was detected for most viruses in this study, and interactions between pairs of meteorological factors were found to enhance their influence on virus variation. These findings might be helpful to guide government planning, such as public health interventions, infection control practice, and timing of passive immunoprophylaxis, and might facilitate the development of future vaccine strategies.

FUNDING

National Natural Science Foundation of China, the Ministry of Science and Technology of China, and the Technology Major Project of China.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

Are meteorological factors enhancing COVID-19 transmission in Bangladesh? Novel findings from a compound Poisson generalized linear modeling approach

Novel coronavirus (SARS-CoV-2) causing COVID-19 disease has arisen to be a pandemic. Since there is a close association between other viral infection cases by epidemics and environmental factors, this study intends to unveil meteorological effects on the outbreak of COVID-19 across eight divisions of Bangladesh from March to April 2020. A compound Poisson generalized linear modeling (CPGLM), along with a Monte-Carlo method and random forest (RF) model, was employed to explore how meteorological factors affecting the COVID-19 transmission in Bangladesh. Results showed that subtropical climate (mean temperature about 26.6 °C, mean relative humidity (MRH) 64%, and rainfall approximately 3 mm) enhanced COVD-19 onset. The CPGLM model revealed that every 1 mm increase in rainfall elevated by 30.99% (95% CI 77.18%, - 15.20%) COVID-19 cases, while an increase of 1 °C of diurnal temperature (TDN) declined the confirmed cases by - 14.2% (95% CI 9.73%, - 38.13%) on the lag 1 and lag 2, respectively. In addition, NRH and MRH had the highest increase (17.98% (95% CI 22.5%, 13.42%) and 19.92% (95% CI: 25.71%, 14.13%)) of COVID-19 cased in lag 4. The results of the RF model indicated that TDN and AH (absolute humidity) influence the COVID-19 cases most. In the Dhaka division, MRH is the most vital meteorological factor that affects COVID-19 deaths. This study indicates the humidity and rainfall are crucial factors affecting the COVID-19 case, which is contrary to many previous studies in other countries. These outcomes can have policy formulation for the suppression of the COVID-19 outbreak in Bangladesh.

Meteorological factors, governmental responses and COVID-19: Evidence from four European countries

With the global lockdown, meteorological factors are highly discussed for COVID-19 transmission. In this study, national-specific and region-specific data sets from Germany, Italy, Spain and the United Kingdom were used to explore the effect of temperature, absolute humidity and diurnal temperature range (DTR) on COVID-19 transmission. From February 1st to November 1st, a 7-day COVID-19 case doubling time (Td), meteorological factors with cumulative 14-day-lagged, government response index and other factors were fitted in the distributed lag nonlinear models. The overall relative risk (RR) of the 10th and the 25th percentiles temperature compared to the median were 0.0074 (95% CI: 0.0023, 0.0237) and 0.1220 (95% CI: 0.0667, 0.2232), respectively. The pooled RR of lower (10th, 25th) and extremely high (90th) absolute humidity were 0.3266 (95% CI: 0.1379, 0.7734), 0.6018 (95% CI: 0.4693, 0.7718) and 0.3438 (95% CI: 0.2254, 0.5242), respectively. While the DTR did not have a significant effect on Td. The total cumulative effect of temperature (10th) and absolute humidity (10th, 90th) on Td increased with the change of lag days. Similarly, a decline in temperature and absolute humidity at cumulative 14-day-lagged corresponded to the lower RR on Td in pooled region-specific effects. In summary, the government responses are important factors in alleviating the spread of COVID-19. After controlling that, our results indicate that both the cold and the dry environment also likely facilitate the COVID-19 transmission.

Study on the decay characteristics and transmission risk of respiratory viruses on the surface of objects

The complex and changeable environment is a brand-new living condition for the viruses and pathogens released by the infected people to the indoor air or deposited on the surface of objects, which is an important external condition affecting the decay and transmission risk of the viruses. Exposure to contaminated surfaces is one of the main routes of respiratory diseases transmission. Therefore, it is very important for epidemic prevention and control to study the law of virus decay and the environmental coupling effect on various surfaces. Based on the analysis of the influencing mechanism, a large amount of experimental evidence on the survival of viruses on the surface of objects were excavated in this paper, and the effects of various factors, such as surface peripheral temperature, relative humidity, virus-containing droplet volume, surface materials and virus types, on the decay rate constants of viruses were comprehensively analyzed. It was found that although the experimental methods, virus types and experimental conditions varied widely in different experiments, the virus concentrations on the surface of objects all followed the exponential decay law, and the coupling effect of various factors was reflected in the decay rate constant k. Under different experimental conditions, k values ranged from 0.001 to 100 h-1, with a difference of 5 orders of magnitude, corresponding to the characteristic time t99 between 500 and 0.1 h when the virus concentration decreased by 99%. This indicates a large variation in the risk of virus transmission in different scenarios. By revealing the common law and individuality of the virus decay on the surface of objects, the essential relationship between the experimental observation phenomenon and virus decay was analyzed. This paper points out the huge difference in virus transmission risk on the surface at different time nodes, and discusses the prevention and control strategies to grasp the main contradictions in the different situations.

Relative humidity in droplet and airborne transmission of disease

A large number of infectious diseases are transmitted by respiratory droplets. How long these droplets persist in the air, how far they can travel, and how long the pathogens they might carry survive are all decisive factors for the spread of droplet-borne diseases. The subject is extremely multifaceted and its aspects range across different disciplines, yet most of them have only seldom been considered in the physics community. In this review, we discuss the physical principles that govern the fate of respiratory droplets and any viruses trapped inside them, with a focus on the role of relative humidity. Importantly, low relative humidity-as encountered, for instance, indoors during winter and inside aircraft-facilitates evaporation and keeps even initially large droplets suspended in air as aerosol for extended periods of time. What is more, relative humidity affects the stability of viruses in aerosol through several physical mechanisms such as efflorescence and inactivation at the air-water interface, whose role in virus inactivation nonetheless remains poorly understood. Elucidating the role of relative humidity in the droplet spread of disease would permit us to design preventive measures that could aid in reducing the chance of transmission, particularly in indoor environment.

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.

A dynamical overview of droplets in the transmission of respiratory infectious diseases

The outbreak of the coronavirus disease has drawn public attention to the transmission of infectious pathogens, and as major carriers of those pathogens, respiratory droplets play an important role in the process of transmission. This Review describes respiratory droplets from a physical and mechanical perspective, especially their correlation with the transmission of infectious pathogens. It covers the important aspects of (i) the generation and expulsion of droplets during respiratory activities, (ii) the transport and evolution of respiratory droplets in the ambient environment, and (iii) the inhalation and deposition of droplets in the human respiratory tract. State-of-the-art experimental, computational, and theoretical models and results are presented, and the corresponding knowledge gaps are identified. This Review stresses the multidisciplinary nature of its subject and appeals for collaboration among different fields to fight the present pandemic.

Health, work performance, and risk of infection in office-like environments: The role of indoor temperature, air humidity, and ventilation

Epidemiological and experimental studies have revealed the effects of the room temperature, indoor air humidity, and ventilation on human health, work and cognitive performance, and risk of infection. In this overview, we integrate the influence of these important microclimatic parameters and assess their influence in offices based on literature searches. The dose-effect curves of the temperature describe a concave shape. Low temperature increases the risk of cardiovascular and respiratory diseases and elevated temperature increases the risk of acute non-specific symptoms, e.g., dry eyes, and respiratory symptoms. Cognitive and work performance is optimal between 22 °C and 24 °C for regions with temperate or cold climate, but both higher and lower temperatures may deteriorate the performances and learning efficiency. Low temperature may favor virus viability, however, depending on the status of the physiological tissue in the airways. Low indoor air humidity causes vulnerable eyes and airways from desiccation and less efficient mucociliary clearance. This causes elevation of the most common mucous membrane-related symptoms, like dry and tired eyes, which deteriorates the work performance. Epidemiological, experimental, and clinical studies support that intervention of dry indoor air conditions by humidification alleviates symptoms of dry eyes and airways, fatigue symptoms, less complaints about perceived dry air, and less compromised work performance. Intervention of dry air conditions by elevation of the indoor air humidity may be a non-pharmaceutical treatment of the risk of infection by reduced viability and transport of influenza virus. Relative humidity between 40 and 60% appears optimal for health, work performance, and lower risk of infection. Ventilation can reduce both acute and chronic health outcomes and improve work performance, because the exposure is reduced by the dilution of the indoor air pollutants (including pathogens, e.g., as virus droplets), and in addition to general emission source control strategies. Personal control of ventilation appears an important factor that influences the satisfaction of the thermal comfort due to its physical and positive psychological impact. However, natural ventilation or mechanical ventilation can become sources of air pollutants, allergens, and pathogens of outdoor or indoor origin and cause an increase in exposure. The "health-based ventilation rate" in a building should meet WHO's air quality guidelines and dilute human bio-effluent emissions to reach an acceptable perceived indoor air quality. Ventilation is a modifying factor that should be integrated with both the indoor air humidity and the room temperature in a strategic joint control to satisfy the perceived indoor air quality, health, working performance, and minimize the risk of infection.

Seasonality of Non-SARS, Non-MERS Coronaviruses and the Impact of Meteorological Factors

Background: Seasonality is a characteristic of some respiratory viruses. The aim of our study was to evaluate the seasonality and the potential effects of different meteorological factors on the detection rate of the non-SARS coronavirus detection by PCR. Methods: We performed a retrospective analysis of 12,763 respiratory tract sample results (288 positive and 12,475 negative) for non-SARS, non-MERS coronaviruses (NL63, 229E, OC43, HKU1). The effect of seven single weather factors on the coronavirus detection rate was fitted in a logistic regression model with and without adjusting for other weather factors. Results: Coronavirus infections followed a seasonal pattern peaking from December to March and plunged from July to September. The seasonal effect was less pronounced in immunosuppressed patients compared to immunocompetent patients. Different automatic variable selection processes agreed on selecting the predictors temperature, relative humidity, cloud cover and precipitation as remaining predictors in the multivariable logistic regression model, including all weather factors, with low ambient temperature, low relative humidity, high cloud cover and high precipitation being linked to increased coronavirus detection rates. Conclusions: Coronavirus infections followed a seasonal pattern, which was more pronounced in immunocompetent patients compared to immunosuppressed patients. Several meteorological factors were associated with the coronavirus detection rate. However, when mutually adjusting for all weather factors, only temperature, relative humidity, precipitation and cloud cover contributed independently to predicting the coronavirus detection rate.

On the Transmission Dynamics of SARS-CoV-2 in a Temperate Climate

An epidemiological model, which describes the transmission dynamics of SARS-CoV-2 under specific consideration of the incubation period including the population with subclinical infections and being infective is presented. The COVID-19 epidemic in Greece was explored through a Monte Carlo uncertainty analysis framework, and the optimal values for the parameters that determined the transmission dynamics could be obtained before, during, and after the interventions to control the epidemic. The dynamic change of the fraction of asymptomatic individuals was shown. The analysis of the modelling results at the intra-annual climatic scale allowed for in depth investigation of the transmission dynamics of SARS-CoV-2 and the significance and relative importance of the model parameters. Moreover, the analysis at this scale incorporated the exploration of the forecast horizon and its variability. Three discrete peaks were found in the transmission rates throughout the investigated period (15 February–15 December 2020). Two of them corresponded to the timing of the spring and autumn epidemic waves while the third one occurred in mid-summer, implying that relaxation of social distancing and increased mobility may have a strong effect on rekindling the epidemic dynamics offsetting positive effects from factors such as decreased household crowding and increased environmental ultraviolet radiation. In addition, the epidemiological state was found to constitute a significant indicator of the forecast reliability horizon, spanning from as low as few days to more than four weeks. Embedding the model in an ensemble framework may extend the predictability horizon. Therefore, it may contribute to the accuracy of health risk assessment and inform public health decision making of more efficient control measures.

Survival of Virus Particles in Water Droplets: Hydrophobic Forces and Landauer's Principle

Many small biological objects, such as viruses, survive in a water environment and cannot remain active in dry air without condensation of water vapor. From a physical point of view, these objects belong to the mesoscale, where small thermal fluctuations with the characteristic kinetic energy of k_BT (where k_B is the Boltzmann’s constant and T is the absolute temperature) play a significant role. The self-assembly of viruses, including protein folding and the formation of a protein capsid and lipid bilayer membrane, is controlled by hydrophobic forces (i.e., the repulsing forces between hydrophobic particles and regions of molecules) in a water environment. Hydrophobic forces are entropic, and they are driven by a system’s tendency to attain the maximum disordered state. On the other hand, in information systems, entropic forces are responsible for erasing information, if the energy barrier between two states of a switch is on the order of k_BT, which is referred to as Landauer’s principle. We treated hydrophobic interactions responsible for the self-assembly of viruses as an information-processing mechanism. We further showed a similarity of these submicron-scale processes with the self-assembly in colloidal crystals, droplet clusters, and liquid marbles.

Accurate Representations of the Microphysical Processes Occurring during the Transport of Exhaled Aerosols and Droplets

Aerosols and droplets from expiratory events play an integral role in transmitting pathogens such as SARS-CoV-2 from an infected individual to a susceptible host. However, there remain significant uncertainties in our understanding of the aerosol droplet microphysics occurring during drying and sedimentation and the effect on the sedimentation outcomes. Here, we apply a new treatment for the microphysical behavior of respiratory fluid droplets to a droplet evaporation/sedimentation model and assess the impact on sedimentation distance, time scale, and particle phase. Above a 100 μm initial diameter, the sedimentation outcome for a respiratory droplet is insensitive to composition and ambient conditions. Below 100 μm, and particularly below 80 μm, the increased settling time allows the exact nature of the evaporation process to play a significant role in influencing the sedimentation outcome. For this size range, an incorrect treatment of the droplet composition, or imprecise use of RH or temperature, can lead to large discrepancies in sedimentation distance (with representative values >1 m, >2 m, and >2 m, respectively). Additionally, a respiratory droplet is likely to undergo a phase change prior to sedimenting if initially <100 μm in diameter, provided that the RH is below the measured phase change RH. Calculations of the potential exposure versus distance from the infected source show that the volume fraction of the initial respiratory droplet distribution, in this size range, which remains elevated above 1 m decreases from 1 at 1 m to 0.125 at 2 m.

Extended Lifetime of Respiratory Droplets in a Turbulent Vapor Puff and Its Implications on Airborne Disease Transmission

To quantify the fate of respiratory droplets under different ambient relative humidities, direct numerical simulations of a typical respiratory event are performed. We found that, because small droplets (with initial diameter of 10  μm) are swept by turbulent eddies in the expelled humid puff, their lifetime gets extended by a factor of more than 30 times as compared to what is suggested by the classical picture by Wells, for 50% relative humidity. With increasing ambient relative humidity the extension of the lifetimes of the small droplets further increases and goes up to around 150 times for 90% relative humidity, implying more than 2 m advection range of the respiratory droplets within 1 sec. Employing Lagrangian statistics, we demonstrate that the turbulent humid respiratory puff engulfs the small droplets, leading to many orders of magnitude increase in their lifetimes, implying that they can be transported much further during the respiratory events than the large ones. Our findings provide the starting points for larger parameter studies and may be instructive for developing strategies on optimizing ventilation and indoor humidity control. Such strategies are key in mitigating the COVID-19 pandemic in the present autumn and upcoming winter.

Airflow Characteristics in Aeromedical Aircraft: Considerations During COVID-19

Objective

The aeromedical transport of coronavirus patients presents risks to clinicians and aircrew. Patient positioning and physical barriers may provide additional protection during flight. This paper describes airflow testing undertaken on fixed wing and rotary wing aeromedical aircraft.

Methods

Airflow testing was undertaken on a stationary Hawker Beechcraft B200C and Leonardo Augusta Westland 139. Airflow was simulated using a Trainer 101 (MSS Professional A/S, Odense Sø, Syddanmark, Denmark) Smoke machine. Different cabin configurations were used along with variations in heating, cooling, and ventilation systems.

Results

For the Hawker Beechcraft B200C, smoke generated within the forward section of the cabin was observed to fill the cabin to a fluid boundary located in-line with the forward edge of the cargo door. With the curtain closed, smoke was only observed to enter the cockpit in very small quantities. For the Leonardo AW139, smoke generated within the cabin was observed to expand to fill the cabin evenly before dissipating. With the curtain closed, smoke was observed to enter the cockpit only in small quantities

Conclusion

The use of physical barriers in fixed wing and rotary wing aeromedical aircraft provides some protection to aircrew. Optimal positioning of the patient is on the aft stretcher on the Beechcraft B200C and on a laterally orientated stretcher on the AW139. The results provide a baseline for further investigation into methods to protect aircrew during the coronavirus pandemic.

Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)

The coronavirus disease 2019 (COVID-19) pandemic has caused untold disruption throughout the world. Understanding the mechanisms for transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is key to preventing further spread, but there is confusion over the meaning of ‘airborne’ whenever transmission is discussed. Scientific ambivalence originates from evidence published many years ago which has generated mythological beliefs that obscure current thinking. This article collates and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six ‘myths’ are presented, explained and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to produce this review to consolidate the evidence for airborne transmission mechanisms, and offer justification for modern strategies for prevention and control of COVID-19 in health care and the community.

Susceptibility of an Airborne Common Cold Virus to Relative Humidity

The viability of airborne respiratory viruses varies with ambient relative humidity (RH). Numerous contrasting reports spanning several viruses have failed to identify the mechanism underlying this dependence. We hypothesized that an "efflorescence/deliquescence divergent infectivity" (EDDI) model accurately predicts the RH-dependent survival of airborne human rhinovirus-16 (HRV-16). We measured the efflorescence and deliquescence RH (RH_E and RH_D, respectively) of aerosols nebulized from a protein-enriched saline carrier fluid simulating the human respiratory fluid and found the RH range of the aerosols' hygroscopic hysteresis zone (RH_E-D) to be 38-68%, which encompasses the preferred RH for indoor air (40-60%). The carrier fluid containing HRV-16 was nebulized into the sub-hysteresis zone (RH_<E) or super-hysteresis zone (RH_>D) air, to set the aerosols to the effloresced/solid or deliquesced/liquid state before transitioning the RH into the intermediate hysteresis zone. The surviving fractions (SFs) of the virus were then measured 15 min post nebulization. SFs were also measured for aerosols introduced directly into the RH_<E, RH_E-D, and RH_>D zones without transition. SFs for transitioned aerosols in the hysteresis zone were higher for effloresced (0.17 ± 0.02) than for deliquesced (0.005 ± 0.005) aerosols. SFs for nontransitioned aerosols in the RH_<E, RH_E-D, and RH_>D zones were 0.18 ± 0.06, 0.05 ± 0.02, and 0.20 ± 0.05, respectively, revealing a V-shaped SF/RH dependence. The EDDI model's prediction of enhanced survival in the hysteresis zone for effloresced carrier aerosols was confirmed.

Direct Quantification of the Effect of Ammonium on Aerosol Droplet pH

Ammonium is an important atmospheric constituent that dictates many environmental processes. The impact of the ammonium ion concentration on 10-50 μm aerosol droplet pH was quantified using pH nanoprobes and surface-enhanced Raman spectroscopy (SERS). Sample solutions were prepared by mixing 1 M ammonium sulfate (AS), ammonium nitrate (AN), sodium sulfate (SS), or sodium nitrate (SN) solutions with 1 M phosphate buffer (PB) at different volume ratios. Stable pH values were measured for pure PB, AS, and AN droplets at different concentrations. The centroid pH of 1 M PB droplets was ∼11, but when PB was systematically replaced with ammonium (AS- or AN-PB), the centroid pH within the droplets decreased from ≈11 to 5.5. Such a decrease was not observed in sodium (SS- or SN-PB) droplets, and no pH differences were observed between sulfate and nitrate salts. Ammonia partitioning to the gas phase in ammonium-containing droplets was evaluated to be negligible. Raman sulfate peak (∼980 cm^-1) intensity measurements and surface tension measurements were conducted to investigate changes in ion distribution. The pH difference between ammonium-containing droplets and ammonium-free droplets is attributed to the alteration of the ion distribution in the presence of ammonium.

The transmission of SARS-CoV-2 is likely comodulated by temperature and by relative humidity

Inferring the impact of climate upon the transmission of SARS-CoV-2 has been confounded by variability in testing, unknown disease introduction rates, and changing weather. Here we present a data model that accounts for dynamic testing rates and variations in disease introduction rates. We apply this model to data from Colombia, whose varied and seasonless climate, central port of entry, and swift, centralized response to the COVID-19 pandemic present an opportune environment for assessing the impact of climate factors on the spread of COVID-19. We observe strong attenuation of transmission in climates with sustained daily temperatures above 30 degrees Celsius and simultaneous mean relative humidity below 78%, with outbreaks occurring at high humidity even where the temperature is high. We hypothesize that temperature and relative humidity comodulate the infectivity of SARS-CoV-2 within respiratory droplets.

Occupational exposure of health care personnel to SARS-CoV-2 particles in the intensive care unit of Tehran hospital

The outbreak of SARS-CoV-2 (COVID-19) has attracted much attention to study its possible presence and airborne transmission. The possibility of COVID-19 airborne transmission in indoor environments is debatable. The present study examined the concentration of viral RNA-containing particles produced directly or indirectly by breathing or coughing of confirmed COVID-19 patients or by carriers without symptoms. Some studies do not accept this method of transmission (COVID-19 airborne transmission). The present study aimed to measure the possible exposure of health care personnel to SARS-CoV-2 particles that may have been suspended in the air to respond to the hypothesis of COVID-19 airborne transmission. Airborne particle sampling was performed using impingement method based on NIOSH (chapter BA) and ASHRAE. Selection of sampling sections was in line with the WHO guidelines. The samples were analyzed using RT-PCR technique. Based on the given results, airborne particles of COVID-19 may present in the air and affect the health of hospital personnel. In fact, the analysis of gene expression in ambient conditions and thereby aerosol transmission of SARS-CoV-2 through air is possible and may lead to occupational exposure of health care personnel. Furthermore, it was found that airborne emission of COVID-19 through the breathing zone of patients, particularly in ICU wards with confirmed cases of COVID-19, may be higher than in other ICU wards. Also, the demonstrated results showed that there is a possibility of reaerosolization (reintroduction) of previously airborne SARS-CoV-2 particles into the atmosphere due to health care personnel frequently walking between different wards and stations of ICU.

Evolution of spray and aerosol from respiratory releases: theoretical estimates for insight on viral transmission

By modelling the evaporation and settling of droplets emitted during respiratory releases and using previous measurements of droplet size distributions and SARS-CoV-2 viral load, estimates of the evolution of the liquid mass and the number of viral copies suspended were performed as a function of time from the release. The settling times of a droplet cloud and its suspended viral dose are significantly affected by the droplet composition. The aerosol (defined as droplets smaller than 5 μm) resulting from 30 s of continued speech has O(1 h) settling time and a viable viral dose an order-of-magnitude higher than in a short cough. The time-of-flight to reach 2 m is only a few seconds resulting in a viral dose above the minimum required for infection, implying that physical distancing in the absence of ventilation is not sufficient to provide safety for long exposure times. The suspended aerosol emitted by continuous speaking for 1 h in a poorly ventilated room gives 0.1-11% infection risk for initial viral loads of 10 8 - 10 10   copies ml l - l , respectively, decreasing to 0.03-3% for 10 air changes per hour by ventilation. The present results provide quantitative estimates useful for the development of physical distancing and ventilation controls.

Survival of the enveloped bacteriophage Phi6 (a surrogate for SARS-CoV-2) in evaporated saliva microdroplets deposited on glass surfaces

Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Saliva and water microdroplets dried out rapidly, within minutes, at all tested RH levels (23%, 43%, 57%, and 78%), while SM microdroplets remained hydrated at RH ≥ 57%. Generally, the survival of all three viruses in dry saliva microdroplets was significantly greater than those in SM buffer and water under all RH (except PhiX174 in water under 57% RH survived the best among 3 media). Thus, atmosphere RH and microdroplet hydration state are not sufficient to explain virus survival, indicating that the virus-suspended medium, and association with saliva components in particular, likely play a role in virus survival. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi6, is thus of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2.

Survival of the enveloped bacteriophage Phi6 (a surrogate for SARS-CoV-2) in evaporated saliva microdroplets deposited on glass surfaces

Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Saliva and water microdroplets dried out rapidly, within minutes, at all tested RH levels (23%, 43%, 57%, and 78%), while SM microdroplets remained hydrated at RH ≥ 57%. Generally, the survival of all three viruses in dry saliva microdroplets was significantly greater than those in SM buffer and water under all RH (except PhiX174 in water under 57% RH survived the best among 3 media). Thus, atmosphere RH and microdroplet hydration state are not sufficient to explain virus survival, indicating that the virus-suspended medium, and association with saliva components in particular, likely play a role in virus survival. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi6, is thus of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2.

Airborne Transmission of COVID-19: Aerosol Dispersion, Lung Deposition, and Virus-Receptor Interactions

Coronavirus disease 2019 (COVID-19), due to infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is now causing a global pandemic. Aerosol transmission of COVID-19, although plausible, has not been confirmed by the World Health Organization (WHO) as a general transmission route. Considering the rapid spread of SARS-CoV-2, especially nosocomial outbreaks and other superspreading events, there is an urgent need to study the possibility of airborne transmission and its impact on the lung, the primary body organ attacked by the virus. Here, we review the complete pathway of airborne transmission of SARS-CoV-2 from aerosol dispersion in air to subsequent biological uptake after inhalation. In particular, we first review the aerodynamic and colloidal mechanisms by which aerosols disperse and transmit in air and deposit onto surfaces. We then review the fundamental mechanisms that govern regional deposition of micro- and nanoparticles in the lung. Focus is given to biophysical interactions between particles and the pulmonary surfactant film, the initial alveolar-capillary barrier and first-line host defense system against inhaled particles and pathogens. Finally, we summarize the current understanding about the structural dynamics of the SARS-CoV-2 spike protein and its interactions with receptors at the atomistic and molecular scales, primarily as revealed by molecular dynamics simulations. This review provides urgent and multidisciplinary knowledge toward understanding the airborne transmission of SARS-CoV-2 and its health impact on the respiratory system.

Maximizing Participant and Staff Safety During Assessment of Physical Function in the COVID-19 Era

Physical performance measures, including cardiopulmonary exercise testing (CPXT), are widely used in geriatric practice and aging research. Theoretically, research participants and study personnel could get infected in the closed environment of the exercise laboratory by contact with respiratory droplets from an infected person, by breathing virus-laden aerosols, or by touching fomites. Older adults are at increased risk of developing more severe disease and of dying from SARS-CoV-2 infection. This special article offers guidance-informed by a synthesis of scientific data and recommendations of the CDC and WHO-on procedures that can be implemented in exercise laboratories to minimize risk of SARS-CoV-2 and other respiratory infections. Most tests of physical function (e.g., gait speed, Short Physical Performance Battery) are not aerosol-generating and are associated with only a small increase in minute ventilation; in contrast, CPXT markedly increases minute ventilation and is potentially aerosol-generating. Researchers should evaluate the benefit-to-risk ratio of information gained from the laboratory assessment versus the risk of SARS-CoV2 infection. Risk mitigation strategies described here fall into four categories: personal hygiene and the use of personal protective equipment; standardized screening; reconfiguration of laboratory space; and optimization of laboratory ventilation. The proposed safety measures are not intended to replace institutional policy, state, or federal guidelines; they may not apply to all settings and are expected to evolve as more definitive information becomes available. These practical measures to maximize protection against SARS-CoV2 infection can help maximize participant and staff safety, reduce anxiety, and facilitate protocol adherence, and study integrity.

Survival of MS2 and Φ6 viruses in droplets as a function of relative humidity, pH, and salt, protein, and surfactant concentrations

The survival of viruses in droplets is known to depend on droplets' chemical composition, which may vary in respiratory fluid between individuals and over the course of disease. This relationship is also important for understanding the persistence of viruses in droplets generated from wastewater, freshwater, and seawater. We investigated the effects of salt (0, 1, and 35 g/L), protein (0, 100, and 1000 μg/mL), surfactant (0, 1, and 10 μg/mL), and droplet pH (4.0, 7.0, and 10.0) on the viability of viruses in 1-μL droplets pipetted onto polystyrene surfaces and exposed to 20%, 50%, and 80% relative humidity (RH) using a culture-based approach. Results showed that viability of MS2, a non-enveloped virus, was generally higher than that of Φ6, an enveloped virus, in droplets after 1 hour. The chemical composition of droplets greatly influenced virus viability. Specifically, the survival of MS2 was similar in droplets at different pH values, but the viability of Φ6 was significantly reduced in acidic and basic droplets compared to neutral ones. The presence of bovine serum albumin protected both MS2 and Φ6 from inactivation in droplets. The effects of sodium chloride and the surfactant sodium dodecyl sulfate varied by virus type and RH. Meanwhile, RH affected the viability of viruses as shown previously: viability was lowest at intermediate to high RH. The results demonstrate that the viability of viruses is determined by the chemical composition of carrier droplets, especially pH and protein content, and environmental factors. These findings emphasize the importance of understanding the chemical composition of carrier droplets in order to predict the persistence of viruses contained in them.

Analyzing the dominant SARS-CoV-2 transmission routes toward an ab initio disease spread model

Identifying the relative importance of the different transmission routes of the SARS-CoV-2 virus is an urgent research priority. To that end, the different transmission routes and their role in determining the evolution of the Covid-19 pandemic are analyzed in this work. The probability of infection caused by inhaling virus-laden droplets (initial ejection diameters between 0.5 µm and 750 µm, therefore including both airborne and ballistic droplets) and the corresponding desiccated nuclei that mostly encapsulate the virions post droplet evaporation are individually calculated. At typical, air-conditioned yet quiescent indoor space, for average viral loading, cough droplets of initial diameter between 10 µm and 50 µm are found to have the highest infection probability. However, by the time they are inhaled, the diameters reduce to about 1/6th of their initial diameters. While the initially near unity infection probability due to droplets rapidly decays within the first 25 s, the small yet persistent infection probability of desiccated nuclei decays appreciably only by O ( 1000 s ) , assuming that the virus sustains equally well within the dried droplet nuclei as in the droplets. Combined with molecular collision theory adapted to calculate the frequency of contact between the susceptible population and the droplet/nuclei cloud, infection rate constants are derived ab initio, leading to a susceptible-exposed-infectious-recovered-deceased model applicable for any respiratory event-vector combination. The viral load, minimum infectious dose, sensitivity of the virus half-life to the phase of its vector, and dilution of the respiratory jet/puff by the entraining air are shown to mechanistically determine specific physical modes of transmission and variation in the basic reproduction numberR 0 from first-principles calculations.

COVID-19 therapy: What weapons do we bring into battle?

Urgent treatments, in any modality, to fight SARS-CoV-2 infections are desired by society in general, by health professionals, by Estate-leaders and, mainly, by the scientific community, because one thing is certain amidst the numerous uncertainties regarding COVID-19: knowledge is the means to discover or to produce an effective treatment against this global disease. Scientists from several areas in the world are still committed to this mission, as shown by the accelerated scientific production in the first half of 2020 with over 25,000 published articles related to the new coronavirus. Three great lines of publications related to COVID-19 were identified for building this article: The first refers to knowledge production concerning the virus and pathophysiology of COVID-19; the second regards efforts to produce vaccines against SARS-CoV-2 at a speed without precedent in the history of science; the third comprehends the attempts to find a marketed drug that can be used to treat COVID-19 by drug repurposing. In this review, the drugs that have been repurposed so far are grouped according to their chemical class. Their structures will be presented to provide better understanding of their structural similarities and possible correlations with mechanisms of actions. This can help identifying anti-SARS-CoV-2 promising therapeutic agents.

Historical Discoveries on Viruses in the Environment and Their Impact on Public Health

BACKGROUND

Transmission of many viruses occurs by direct transmission during a close contact between two hosts, or by an indirect transmission through the environment. Several and often interconnected factors, both abiotic and biotic, determine the persistence of these viruses released in the environment, which can last from a few seconds to several years. Moreover, viruses in the environment are able to travel short to very long distances, especially in the air or in water.

SUMMARY

Although well described now, the role of these environments as intermediaries or as reservoirs in virus transmission has been extensively studied and debated in the last century. The majority of these discoveries, such as the pioneer work on bacteria transmission, the progressive discoveries of viruses, as well as the persistence of the influenza virus in the air varying along with droplet sizes, or the role of water in the transmission of poliovirus, have contributed to the improvement of public health. Recent outbreaks of human coronavirus, influenza virus, and Ebola virus have also demonstrated the contemporaneity of these research studies and the need to study virus persistence in the environment. Key Messages: In this review, we discuss historical discoveries that contributed to describe biotic and abiotic factors determining viral persistence in the environment.

A Risk-Based Approach to the COVID-19 Pandemic: The Experience in National Dental Centre Singapore

The emergence of a highly infectious coronavirus strain, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a major global public health emergency. The increasing number of infected cases and fatalities worldwide forced several countries into lockdown in a bid to control virus transmission. The practice of dentistry is considered high-risk due to the generation of aerosols associated with most dental procedures, and healthcare professionals must take appropriate precautions whilst working in this challenging environment. This review aims to provide an overview on transmission routes and shares a risk-based approach to coronavirus disease 2019 (COVID-19) in a specialty tertiary center. Risk assessment and mitigation focussed on staff and patient safety, adopting a wide safety margin, and responding dynamically to the level of risk at the workplace. As the severity of the pandemic depends on many still-unknown factors and shows little sign of abating, the routine practice of dentistry will continue to be disrupted in the near future. We describe a color-coded framework to maximize safety and to minimize disease spread. Areas covered include healthcare team management, personal protective equipment, clinical work, and dental education. Guidelines in each category change with the corresponding severity of the situation, and we believe it will be useful for the safer practice of dentistry in this current climate and can be modified for future similar disease outbreaks.

Meteorological impact on the COVID-19 pandemic: A study across eight severely affected regions in South America

The role of meteorological factors in the transmission of the COVID-19 still needs to be determined. In this study, the daily new cases of the eight severely affected regions in four countries of South America and their corresponding meteorological data (average temperature, maximum temperature, minimum temperature, average wind speed, visibility, absolute humidity) were collected. Daily number of confirmed and incubative cases, as well as time-dependent reproductive number (R_t) was calculated to indicate the transmission of the diseases in the population. Spearman's correlation coefficients were assessed to show the correlation between meteorological factors and daily confirmed cases, daily incubative cases, as well as Rt. In particular, the results showed that there was a highly significant correlation between daily incubative cases and absolute humidity throughout the selected regions. Multiple linear regression model further confirmed the negative correlation between absolute humidity and incubative cases. The absolute humidity is predicted to show a decreasing trend in the coming months from the meteorological data of recent three years. Our results suggest the necessity of continuous controlling policy in these areas and some other complementary strategies to mitigate the contagious rate of the COVID-19.

Association of climatic factors with COVID-19 in Pakistan

INTRODUCTION

Environmental factors such as wind, temperature, humidity, and sun exposure are known to affect influenza and viruses such as severe acute respiratory syndrome (SARS) and Middle East Respiratory Syndrome (MERS) transmissions. COVID-19 is a new pandemic with very little information available about its transmission and association with environmental factors. The goal of this paper is to explore the association of environmental factors on daily incidence rate, mortality rate, and recoveries of COVID-19.

METHODS

The environmental data for humidity, temperature, wind, and sun exposure were recorded from metrological websites and COVID-19 data such as the daily incidence rate, death rate, and daily recovery were extracted from the government's official website available to the general public. The analysis for each outcome was adjusted for factors such as lock down status, nationwide events, and the number of daily tests performed. Analysis was completed with negative binominal regression log link using generalised linear modelling.

RESULTS

Daily temperature, sun exposure, wind, and humidity were not significantly associated with daily incidence rate. Temperature and nationwide social gatherings, although non-significant, showed trends towards a higher chance of incidence. An increase in the number of daily testing was significantly associated with higher COVID-19 incidences (effect size ranged from 2.17-9.96). No factors were significantly associated with daily death rates. Except for the province of Balochistan, a lower daily temperature was associated with a significantly higher daily recovery rate.

DISCUSSION

Environmental factors such as temperature, humidity, wind, and daily sun exposure were not consistently associated with COVID-19 incidence, death rates, or recovery. More policing about precautionary measures and ensuring diagnostic testing and accuracy are needed.

Transformative Approach To Investigate the Microphysical Factors Influencing Airborne Transmission of Pathogens

Emerging outbreaks of airborne pathogenic infections worldwide, such as the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, have raised the need to understand parameters affecting the airborne survival of microbes in order to develop measures for effective infection control. We report a novel experimental strategy, TAMBAS (tandem approach for microphysical and biological assessment of airborne microorganism survival), to explore the synergistic interactions between the physicochemical and biological processes that impact airborne microbe survival in aerosol droplets. This innovative approach provides a unique and detailed understanding of the processes taking place from aerosol droplet generation through to equilibration and viability decay in the local environment, elucidating decay mechanisms not previously described. The impact of evaporation kinetics, solute hygroscopicity and concentration, particle morphology, and equilibrium particle size on airborne survival are reported, using Escherichia coli MRE162 as a benchmark system. For this system, we report that (i) particle crystallization does not directly impact microbe longevity, (ii) bacteria act as crystallization nuclei during droplet drying and equilibration, and (iii) the kinetics of size and compositional change appear to have a larger effect on microbe longevity than the equilibrium solute concentration.IMPORTANCE A transformative approach to identify the physicochemical processes that impact the biological decay rates of bacteria in aerosol droplets is described. It is shown that the evaporation process and changes in the phase and morphology of the aerosol particle during evaporation impact microorganism viability. The equilibrium droplet size was found to affect airborne bacterial viability. Furthermore, the presence of Escherichia coli MRE162 in a droplet does not affect aerosol growth/evaporation but influences the dynamic behavior of the aerosol by processing the culture medium prior to aerosolization, affecting the hygroscopicity of the culture medium; this highlights the importance of the inorganic and organic chemical composition within the aerosolized droplets that impact hygroscopicity. Bacteria also act as crystallization nuclei. The novel approach and data have implications for increased mechanistic understanding of aerosol survival and infectivity in bioaerosol studies spanning the medical, veterinary, farming, and agricultural fields, including the role of microorganisms in atmospheric processing and cloud formation.

Fate of respiratory droplets in tropical vs temperate environments and implications for SARS-CoV-2 transmission

The new pandemic of SARS-CoV-2 has shown stark differences in number of affected patients between countries in the tropics and those with temperate environments. Though there have been many theories on reasons for these differences, we hypothesise that this could be due to differences in the fate of respiratory droplets in the two environments. A simple understanding of the mechanics of droplet size, dispersion and displacement could help infection control and public health measures to minimize spread and mitigate the risk of people getting infected especially in hotspots like hospital environments or other closed spaces. This paper discusses the possibility of differences in number of infections and spread between different countries based on the spread of droplets.

Solid Oxygen-Purifying (SOP) Filters: A Self-Disinfecting Filters to Inactivate Aerosolized Viruses

Normal heating, ventilation, and air conditioning (HVAC) systems typically use high-efficiency particulate air (HEPA) filters, which can filter dust, various pollutants, and even bacteria and viruses from indoor air. However, since HEPA filters cannot not clean themselves and due to the nature of these microbes which can survive for long periods of time, changing these filters improperly could transmit pathogenic bacteria or viruses, and could even lead to new infections. This study indicated that these manufactured Solid Oxygen-purifying (SOP) filters have the potential to self-disinfect, filter, and inactivate aerosolized viruses. MS2 bacteriophage was used as a model virus in two different experiments. The first experiment involved aerosolization of the virus, while the second were a higher viral load using a soaking method. The SOP filters inactivated up to 99.8% of the virus particles in both experiments, provided that the density of the SOP filter was high. Thus, SOP filters could self-clean, which led to protection against airborne and aerosolized viruses by inactivating them on contact. Furthermore, SOP filters could be potentially use or addition in HVAC systems and face masks to prevent the transmission of airborne and aerosolized viruses.

Investigation of the Importance of Climatic Factors in COVID-19 Worldwide Intensity

The transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the severity of the related disease (COVID-19) are influenced by a large number of factors. This study aimed to investigate the correlation of COVID-19 case and death rates with possible causal climatological and sociodemographic factors for the March to May 2020 (first wave) period in a worldwide scale by statistically processing data for over one hundred countries. The weather parameters considered herein were air temperature, relative humidity, cumulative precipitation, and cloud cover, while sociodemographic factors included population density, median age, and government measures in response to the pandemic. The results of this study indicate that there is a statistically significant correlation between average atmospheric temperature and the COVID-19 case and death rates, with chi-square test p-values in the 0.001-0.02 range. Regarding sociodemographic factors, there is an even stronger dependence of the case and death rates on the population median age (p = 0.0006-0.0012). Multivariate linear regression analysis using Lasso and the forward stepwise approach revealed that the median age ranks first in importance among the examined variables, followed by the temperature and the delays in taking first governmental measures or issuing stay-at-home orders.

Assessing the relationship between surface levels of PM2.5 and PM10 particulate matter impact on COVID-19 in Milan, Italy

The novel coronavirus disease (COVID-19) is a highly pathogenic, transmittable and invasive pneumococcal disease caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which emerged in December 2019 and January 2020 in Wuhan city, Hubei province, China and fast spread later on the middle of February 2020 in the Northern part of Italy and Europe. This study investigates the correlation between the degree of accelerated diffusion and lethality of COVID-19 and the surface air pollution in Milan metropolitan area, Lombardy region, Italy. Daily average concentrations of inhalable particulate matter (PM) in two size fractions PM2.5, PM10 and maxima PM10 ground level atmospheric pollutants together air quality and climate variables (daily average temperature, relative humidity, wind speed, atmospheric pressure field and Planetary Boundary Layer-PBL height) collected during 1 January-30 April 2020 were analyzed. In spite of being considered primarily transmitted by indoor bioaerosols droplets and infected surfaces, or direct human-to-human personal contacts, it seems that high levels of urban air pollution, weather and specific climate conditions have a significant impact on the increased rates of confirmed COVID-19 Total number, Daily New and Total Deaths cases, possible attributed not only to indoor but also to outdoor airborne bioaerosols distribution. Our analysis demonstrates the strong influence of daily averaged ground levels of particulate matter concentrations, positively associated with average surface air temperature and inversely related to air relative humidity on COVID-19 cases outbreak in Milan. Being a novel pandemic coronavirus (SARS-CoV-2) version, COVID-19 might be ongoing during summer conditions associated with higher temperatures and low humidity levels. Presently is not clear if this protein "spike" of the new coronavirus COVID-19 is involved through attachment mechanisms on indoor or outdoor airborne aerosols in the infectious agent transmission from a reservoir to a susceptible host in some agglomerated urban areas like Milan is.

Assessing the relationship between surface levels of PM2.5 and PM10 particulate matter impact on COVID-19 in Milan, Italy

The novel coronavirus disease (COVID-19) is a highly pathogenic, transmittable and invasive pneumococcal disease caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which emerged in December 2019 and January 2020 in Wuhan city, Hubei province, China and fast spread later on the middle of February 2020 in the Northern part of Italy and Europe. This study investigates the correlation between the degree of accelerated diffusion and lethality of COVID-19 and the surface air pollution in Milan metropolitan area, Lombardy region, Italy. Daily average concentrations of inhalable particulate matter (PM) in two size fractions PM2.5, PM10 and maxima PM10 ground level atmospheric pollutants together air quality and climate variables (daily average temperature, relative humidity, wind speed, atmospheric pressure field and Planetary Boundary Layer-PBL height) collected during 1 January-30 April 2020 were analyzed. In spite of being considered primarily transmitted by indoor bioaerosols droplets and infected surfaces, or direct human-to-human personal contacts, it seems that high levels of urban air pollution, weather and specific climate conditions have a significant impact on the increased rates of confirmed COVID-19 Total number, Daily New and Total Deaths cases, possible attributed not only to indoor but also to outdoor airborne bioaerosols distribution. Our analysis demonstrates the strong influence of daily averaged ground levels of particulate matter concentrations, positively associated with average surface air temperature and inversely related to air relative humidity on COVID-19 cases outbreak in Milan. Being a novel pandemic coronavirus (SARS-CoV-2) version, COVID-19 might be ongoing during summer conditions associated with higher temperatures and low humidity levels. Presently is not clear if this protein "spike" of the new coronavirus COVID-19 is involved through attachment mechanisms on indoor or outdoor airborne aerosols in the infectious agent transmission from a reservoir to a susceptible host in some agglomerated urban areas like Milan is.

A review on prediction of seasonal diseases based on climate change using big data

Big Data occupies an important place in the prediction of diseases that happen due to climate change. In each aspect of human life, the weather plays a major role. It directly affects human society or human life. Because of an extreme weather condition creates various diseases among humans. Such as Vector-borne diseases (Malaria, dengue and chikungunya fever), Water-borne diseases (Cholera, Typhoid), Air-borne diseases (Chicken Pox, influenza and small Pox) and Food-borne diseases (Diarrhoea and Salmonella) etc. This survey presents an overview for a climate variable such as extreme temperature, precipitation, humidity and how unexpected climate conditions can affect the disease and living organism.

Effects of ventilation on the indoor spread of COVID-19

Although the relative importance of airborne transmission of the SARS-CoV-2 virus is controversial, increasing evidence suggests that understanding airflows is important for estimation of the risk of contracting COVID-19. The data available so far indicate that indoor transmission of the virus far outstrips outdoor transmission, possibly due to longer exposure times and the decreased turbulence levels (and therefore dispersion) found indoors. In this paper we discuss the role of building ventilation on the possible pathways of airborne particles and examine the fluid mechanics of the processes involved.

Soft matter science and the COVID-19 pandemic

Much of the science underpinning the global response to the COVID-19 pandemic lies in the soft matter domain. Coronaviruses are composite particles with a core of nucleic acids complexed to proteins surrounded by a protein-studded lipid bilayer shell. A dominant route for transmission is via air-borne aerosols and droplets. Viral interaction with polymeric body fluids, particularly mucus, and cell membranes controls their infectivity, while their interaction with skin and artificial surfaces underpins cleaning and disinfection and the efficacy of masks and other personal protective equipment. The global response to COVID-19 has highlighted gaps in the soft matter knowledge base. We survey these gaps, especially as pertaining to the transmission of the disease, and suggest questions that can (and need to) be tackled, both in response to COVID-19 and to better prepare for future viral pandemics.

Modeling Evaporation of Water Droplets as Applied to Survival of Airborne Viruses

Many viruses, such as coronaviruses, tend to spread airborne inside water microdroplets. Evaporation of the microdroplets may result in a reduction of their contagiousness. However, the evaporation of small droplets is a complex process involving mass and heat transfer, diffusion, convection and solar radiation absorption. Virological studies indicate that airborne virus survival is very sensitive to air humidity and temperature. We employ a model of droplet evaporation with the account for the Knudsen layer. This model suggests that evaporation is sensitive to both temperature and the relative humidity (RH) of the ambient air. We also discuss various mechanisms such as the effect of solar irradiation, the dynamic relaxation of moving droplets in ambient air and the gravitational sedimentation of the droplets. The maximum estimate for the spectral radiative flux in the case of cloudless sky showed that the radiation contribution to evaporation of single water droplets is insignificant. We conclude that at small and even at moderately high levels of RH, microdroplets evaporate within dozens of seconds with the convective heat flux from the air being the dominant mechanism in every case. The numerical results obtained in the paper are in good qualitative agreement with both the published laboratory experiments and seasonal nature of many viral infections. Sophisticated experimental techniques may be needed for in situ observation of interaction of viruses with organic particles and living cells within microdroplets. The novel controlled droplet cluster technology is suggested as a promising candidate for such experimental methodology.