Deposition features of inhaled viral droplets may lead to rapid secondary transmission of COVID-19

Effect of temperature on fast transmission of COVID-19 in low per capita GDP Asian countries

An abrupt outbreak of COVID-19 caused enormous global concerns. Although all countries around the world are severely affected, developing Asian countries faced more difficulties due to their low per capita GDP. The temperature was considered a leading variable in spreading viral diseases, including COVID-19. The present study aimed to assess the relationship between temperature and the spread of COVID-19, with a focus on developing Asian countries. In a few Asian countries, COVID-19 spread rapidly in the summer, while in some countries, there is an increase in winter. A linear correlation was developed between COVID-19 cases/deaths and temperature for the selected countries, which were very weak. A coefficient of determination of 0.334 and 0.365 was observed between cases and average monthly max/min temperatures. A correlation of R2 = 0.307 and 0.382 was found between deaths and average max/min monthly temperatures, respectively. There is no scientific reason to assume that COVID-19 is more dominant at low than high temperatures. Therefore, it is believed that the results may be helpful for the health department and decision-makers to understand the fast spread of COVID-19.

Three Experimental Common High-Risk Procedures: Emission Characteristics Identification and Source Intensity Estimation in Biosafety Laboratory

Biosafety laboratory is an important place to study high-risk microbes. In biosafety laboratories, with the outbreak of infectious diseases such as COVID-19, experimental activities have become increasingly frequent, and the risk of exposure to bioaerosols has increased. To explore the exposure risk of biosafety laboratories, the intensity and emission characteristics of laboratory risk factors were investigated. In this study, high-risk microbe samples were substituted with Serratia marcescens as the model bacteria. The resulting concentration and particle size segregation of the bioaerosol produced by three experimental procedures (spill, injection, and sample drop) were monitored, and the emission sources' intensity were quantitatively analyzed. The results showed that the aerosol concentration produced by injection and sample drop was 103 CFU/m3, and that by sample spill was 102 CFU/m3. The particle size of bioaerosol is mainly segregated in the range of 3.3-4.7 μm. There are significant differences in the influence of risk factors on source intensity. The intensity of sample spill, injection, and sample drop source is 3.6 CFU/s, 78.2 CFU/s, and 664 CFU/s. This study could provide suggestions for risk assessment of experimental operation procedures and experimental personnel protection.

Influence of indoor environmental conditions on airborne transmission and lifetime of sneeze droplets in a confined space: a way to reduce COVID-19 spread

Effects of indoor temperature (T∞) and relative humidity (RH∞) on the airborne transmission of sneeze droplets in a confined space were studied over the T∞ range of 15-30 °C and RH∞ of 22-62%. In addition, a theoretical evaporation model was used to estimate the droplet lifetime based on experimental data. The results showed that the body mass index (BMI) of the participants played an important role in the sneezing jet velocity, while the impact of the BMI and gender of participants was insignificant on the size distribution of droplets. At a critical relative humidity RH∞,crit of 46%, the sneezing jet velocity and droplet lifetime were roughly independent of T∞. At RH∞ < RH∞,crit, the sneezing jet velocity decreased by increasing T∞ from 15 to 30 °C, while its trend was reversed at RH∞ > RH∞,crit. The maximum spreading distance of aerosols increased by decreasing the RH∞ and increasing T∞, while the droplet lifetime increased by decreasing T∞ at RH∞ > RH∞,crit. The mean diameter of aerosolized droplets was less affected by T∞ than the large droplets at RH∞ < RH∞,crit, while the mean diameter and number fraction of aerosols were more influenced by RH∞ than the T∞ in the range of 46% ≤ RH∞ ≤ 62%. In summary, this study suggests suitable indoor environmental conditions by considering the transmission rate and lifetime of respiratory droplets to reduce the spread of COVID-19.

Safe Distance of Virus Quantitative Analysis and Simulation of the Trajectory of Pathogen-Containing Droplets in the Air Respiratory Airways

Droplets of mucosalivary ejecta emitted by sneezing or coughing are a major carrier of numerous types of bacterial and viral diseases. This study develops a numerical model to estimate the spread distance for inhalable droplets (1–50 μm) in the air, the inhalability of the particles, and the trajectory as well as velocity of these pathogen-containing droplets in human respiratory airways. Moreover, particularly for droplets with diameters of 1 μm, 5 μm, 10 μm, and 50 μm, specific comparisons between their inhalability and transmission velocities are made. Data extracted from previous experiments proceeded by other researchers discussing the visualization of sneeze ejecta and deposition features of inhaled drops were used to obtain parameters to fit the model prediction of this work. Currently, research on similar topics was mostly based on either experiments or theoretical calculations only on one specific clan of pathogen, while the novel contribution of this paper is the combination and comparison of these two distinct methodologies that can be applied to solve a general practical problem aiming to all types of viruses by considering the pathogen-containing droplets as a whole entity.

An improved numerical model for epidemic transmission and infection risks assessment in indoor environment

Social distance will remain the key measure to contain COVID-19 before the global widespread vaccination coverage expected in 2024. Containing the virus outbreak in the office is prioritised to relieve socio-economic burdens caused by COVID-19 and potential pandemics in the future. However, "what is the transmissible distance of SARS-CoV-2" and "what are the appropriate ventilation rates in the office" have been under debate. Without quantitative evaluation of the infection risk, some studies challenged the current social distance policies of 1-2 m adopted by most countries and suggested that longer social distance rule is required as the maximum transmission distance of cough ejected droplets could reach 3-10 m. With the emergence of virus variants such as the Delta variant, the applicability of previous social distance rules are also in doubt. To address the above problem, this study conducted transient Computational Fluid Dynamics (CFD) simulations to evaluate the infection risks under calm and wind scenarios. The calculated Social Distance Index (SDI) indicates that lower humidity leads to a higher infection risk due to weaker evaporation. The infection risk in office was found more sensitive to social distance than ventilation rate. In standard ventilation conditions, social distance of 1.7 m-1.8 m is sufficient distances to reach low probability of infection (PI) target in a calm scenario when coughing is the dominant transmission route. However in the wind scenario (0.25 m/s indoor wind), distance of 2.8 m is required to contain the wild virus type and 3 m is insufficient to contain the spread of the Delta variant. The numerical methods developed in this study provide a framework to evaluate the COVID-19 infection risk in indoor environment. The predicted PI will be beneficial for governments and regulators to make appropriate social-distance and ventilation rules in the office.

Ventilation in worker dormitories and its impact on the spread of respiratory droplets

Most of the COVID-19 cases in Singapore have primarily come from foreign worker dormitories. This people group is especially vulnerable partly because of behavioural habits, but the built environment they live in also plays a significant role. These dormitories are typically densely populated, so the living conditions are cramped. The short lease given to most dormitories also means the design does not typically focus on environmental performance, like good natural ventilation. This paper seeks to understand how these dormitories' design affects natural ventilation and, subsequently, the spread of the COVID-19 particles by looking at two existing worker dorms in Singapore. Findings show that some rooms are poorly orientated against the prevailing wind directions, so there is dominant stagnant air in these rooms, leading to respiratory droplets' long residence times. These particles can hover in the air for 10 min and more. Interventions like increased bed distance and removing upper deck beds only showed limited ventilation improvements in some rooms. Comparatively, internal wind scoops' strategic placement was more effective at directing wind towards more stagnant zones. Large canyon aspect ratios were also effective at removing particles from higher elevations.

The impact of coronavirus SARS-CoV-2 (COVID-19) in water: potential risks

This review summarizes research data on SARS-CoV-2 in water environments. A literature survey was conducted using the electronic databases Science Direct, Scopus, and Springer. This complete research included and discussed relevant studies that involve the (1) introduction, (2) definition and features of coronavirus, (2.1) structure and classification, (3) effects on public health, (4) transmission, (5) detection methods, (6) impact of COVID-19 on the water sector (drinking water, cycle water, surface water, wastewater), (6.5) wastewater treatment, and (7) future trends. The results show contamination of clean water sources, and community drinking water is vulnerable. Additionally, there is evidence that sputum, feces, and urine contain SARS-CoV-2, which can maintain its viability in sewage and the urban-rural water cycle to move towards seawater or freshwater; thus, the risk associated with contracting COVID-19 from contact with untreated water or inadequately treated wastewater is high. Moreover, viral loads have been detected in surface water, although the risk is lower for countries that efficiently treat their wastewater. Further investigation is immediately required to determine the persistence and mobility of SARS-CoV-2 in polluted water and sewage as well as the possible potential of disease transmission via drinking water. Conventional wastewater treatment systems have been shown to be effective in removing the virus, which plays an important role in pandemic control. Monitoring of this virus in water is extremely important as it can provide information on the prevalence and distribution of the COVID-19 pandemic in different communities as well as possible infection dynamics to prevent future outbreaks.