Effects of occupant behavior and ventilation on exposure to respiratory droplets in the indoor environment

To quantify the risk of the transmission of respiratory infections in indoor environments, we systematically assessed exposure to talking- and breathing-generated respiratory droplets in a generic indoor environment using computational fluid dynamic (CFD) simulations. The flow field in the indoor environment was obtained with SST k-ω model and Lagrangian method was used to predict droplet trajectories, where droplet evaporation was considered. Droplets can be categorized into small droplets (initial size ≤30 μm or ≤10 μm as droplet nuclei), medium droplets (30–80 μm) and large droplets (>100 μm) according to the exposure characteristics. Droplets up to 100 μm, particular the small ones, can contribute to both short-range and long-range airborne routes. For the face-to-face talking scenario, the intake fraction and deposition fractions of droplets on the face and facial mucosa of the susceptible were up to 4.96%, 2.14%, and 0.12%, respectively, indicating inhalation is the dominant route. The exposure risk from a talking infector decreases monotonically with the interpersonal distance, while that of nasal-breathing generated droplets maintains a relatively stable level within 1.0 m. Keeping an angle of 15° or above with the expiratory flow is efficient to reduce intake fractions to <0.37% for small droplets. Adjusting the orientation from face-to-face to face-to-back can reduce exposure to small droplets by approximately 88.0% during talking and 66.2% during breathing. A higher ventilation rate can reduce the risk of exposure to small droplets but may increase the risk of transmission via medium droplets by enhancing their evaporation rate. This study would serve as a fundamental research for epidemiologist, healthcare workers and the public in the purpose of infection control. © 2023 Elsevier Ltd

SARS-CoV-2 nucleocapsid protein: Importance in viral infection

The coronavirus disease 2019 (COVID-19) epidemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused millions of deaths worldwide. Therefore, it is critical to understand the biological basis of SARS-CoV-2 to develop novel approaches to control its spread. The SARS-CoV-2 nucleocapsid (N) protein is an important diagnostic and potent therapeutic target of the disease, as it is involved in numerous important functions in the viral life cycle. Several studies have explained the structural and functional aspects of the SARS-CoV-2 N protein. This review summarizes the currently available data on the evolutionarily conserved N protein of SARS-CoV-2 by providing detailed information on the structural and multifunctional characteristics of the N protein. © 2022 The Author(s).

Immune Evasion by the Highly Mutated SARS-CoV-2 Omicron Variant

The currently circulating SARS-CoV-2 Omicron variant posed a big challenge for the ongoing pandemic prevention and control activities. The critical concern is whether the current vaccines and therapeutics are capable of fully controlling this variant. Omicron has several mutations mainly concentrated in the receptor-binding domain (RBD) which is the main target for neutralizing antibodies and vaccine-elicited sera, and it is reportedly evading immunity. However, the degree to which the Omicron evades immunity and its impact on the prevention and control activities requires recent and continuous scrutiny. Despite several reports are available, updated and recent discussions are important to tackle the ongoing pandemic especially due to the emerging SARS-CoV-2 variants. Therefore, new insights on designing effective preventive and control measures is utmost important. This review discusses the extent of immune evasion by the Omicron variant and forwards important directions which could have valuable contributions to design alternative strategies in fighting against SARS-Co-2 variants.

Numerical investigation on the origin of virus-laden droplets in the respiratory tract

There have been over 17 million COVID-19 infections worldwide up to July 31, 2020, but the exact transmission route remains a subject for debate. Virus load in different-sized respiratory droplets is the key to address the above question. Investigation on the droplet deposition characteristics during exhalation inside the respiratory tract will facilitate the understanding of their origin and importance in transmitting the respiratory infection. Based on a realistic respiratory model, this study utilized the computational fluid dynamic (CFD) simulation to investigate the deposition of droplets originating from infection sites like pharynx, larynx and trachea under three flow conditions, namely 30 L/min (representing the normal breathing condition), 60 L/min (speaking) and 180 L/min (coughing). The SST k-ω turbulence model integrated in ANSYS Fluent software was utilized to obtain the flow field inside the respiratory tract by solving the continuity and momentum equations, and the Lagrangian approach was used to calculate droplet motion and deposition with the discrete random walk model to account for the turbulence fluctuation effect. Evaporation of droplets was not considered inside the saturated respiratory tract. Droplet diameter, flow rate of the exhaling air, and complexity of the respiratory tract geometry are the most important factors in determining the deposition pattern of respiratory droplets. It is revealed that the largest droplet that originates from the joint of pharynx and larynx and is able to escape out of the respiratory tract is about 20 µm (30 L/min) or 10 µm(60-180 L/min) in diameter;the so-called cut-off sizes for vocal cord and trachea originated droplets are 7 µm (30 L/min), 5 µm (60 L/min) or 3 µm (180 L/min). Larynx and joint of larynx and pharynx are the most important deposition sites due to their complexity in geometry and the existence of the laryngeal jet, whose velocity is up to 102 m/s during coughing and32 m/s during speaking;the nasal cavity is also effective in trapping relatively small droplets as the airflow has a sudden change in direction before entering the oral cavity. Under the investigated speaking scenario (60 L/min), the escape rate of1 µm droplets is around 50%, and the maximum escape rates of 5 and 10 µm droplets are respectively 13.1% and 1.3% (originating from the joint of pharynx and larynx). Although large droplets up to several hundred micrometers can be produced inside the oral cavity due to the atomization mechanism, they seldom carry pathogen. Thus, for COVID-19 patents in the early stage of infection who show upper respiratory symptoms, the cut-off size of virus-laden droplets released into the environment is about 20 µm;with the shifting of infection to the lower respiratory tract in the later stage, the cut-off size decreases to 7 µm. Respiratory droplets evaporate immediately after escaping into the indoor environments and shrink to about one third of their initial size, so airborne route is speculated to be important in the transmission of COVID-19. Further investigations considering realistic flow conditions together with droplet sampling experiments on human volunteers are necessary to confirm these cut-off sizes. © 2021, Science Press. All right reserved.

Effectiveness of anti-pressure protective mask for medical personnel fighting against coronavirus disease 2019

Objective To evaluate the effectiveness of anti-pressure protective mask for medical personnel fighting against the coronavirus disease 2019 (COVID-19). Methods Convenience sampling method was used to select 120 military frontline anti-epidemic medical personnel supporting Wuhan medical team from Jan. 26 to Feb. 24, 2020, and they were evenly divided into blank group, control group and observation group. The blank group did not use anti-pressure dressings, the control group wore face protection equipments after using hydrocolloid dressings, and the observation group wore face protection equipments after using anti-pressure protective mask. At the end of the intervention, the facial comfort, facial pressure injuries, and adverse effects were compared between the three groups. Results At the end of the intervention, the facial comfort score was 6.00 (6.00, 7.00) in the blank group, 5.00 (4.00, 5.00) in the control group, and 1.00 (0.50, 2.00) in the observation group, with significant differences found among the three groups (H=97.392, P<0.001). According to the further inference of the rank mean, the blank group had the largest facial comfort rank mean (96.68), while the observation group had the smallest facial comfort rank mean (20.88). At the end of the intervention, three cases (7.5%, 3/40) in the blank group had no facial injury, 28 cases (70.0%, 28/40) had facial pressure injury at stage 1, and nine cases (22.5%, 9/40) at stage 2;27 cases (67.5%, 27/40) in the control group had no facial injury and 13 cases (32.5%, 13/40) had facial pressure injury at stage 1;37 cases (92.5%, 37/40) in the observation group had no facial injury and three cases (7.5%, 3/40) had facial pressure injury at stage 1. There was significant difference in the incidence of facial pressure injuries among the three groups (χ2=71.863, P<0.001). The observation group had the lowest facial pressure injury rate among the three groups. There was no skin allergic reaction in the three groups and none of them was infected with COVID-19. Conclusion Anti-pressure protective mask can effectively reduce the incidence of facial pressure injuries and improve the facial comfort when wearing facial protective equipment, and it can be used for protecting frontline anti-epidemic medical personnel.

Multi-route transmission potential of SARS-CoV-2 in healthcare facilities

Understanding the transmission mechanism of SARS-CoV-2 is a prerequisite to effective control measures. To investigate the potential modes of SARS-CoV-2 transmission, 21 COVID-19 patients from 12-47 days after symptom onset were recruited. We monitored the release of SARS-CoV-2 from the patients' exhaled breath and systematically investigated environmental contamination of air, public surfaces, personal necessities, and the drainage system. SARS-CoV-2 RNA was detected in 0 of 9 exhaled breath samples, 2 of 8 exhaled breath condensate samples, 1 of 12 bedside air samples, 4 of 132 samples from private surfaces, 0 of 70 samples from frequently touched public surfaces in isolation rooms, and 7 of 23 feces-related air/surface/water samples. The maximum viral RNA concentrations were 1857 copies/m3 in the air, 38 copies/cm2 in sampled surfaces and 3092 copies/mL in sewage/wastewater samples. Our results suggest that nosocomial transmission of SARS-CoV-2 can occur via multiple routes. However, the low detection frequency and limited quantity of viral RNA from the breath and environmental specimens may be related to the reduced viral load of the COVID-19 patients on later days after symptom onset. These findings suggest that the transmission dynamics of SARS-CoV-2 differ from those of SARS-CoV in healthcare settings.