Outward and inward protection efficiencies of different mask designs for different respiratory activities

We evaluate the outward and inward protection efficiencies of different mask types (N95, surgical and two cloth mask designs) taking into account the imperfect fit on the wearer. To this end, we built a manikin to simulate exhaling, coughing and inhaling of aerosol droplets 0.3–5.0μm in diameters. The protection efficiencies depend on many factors, including the droplet size, the mask fit and the presence of a filter layer. Here, we show that cloth and surgical masks with a non-woven filter layer can achieve a combined outward and inward protection efficiencies between 50% and 90%. Removing the filter layer greatly reduces the protection efficiency to below 20% for the smallest droplet size. While a well-fitted N95 masks offer protection efficiency close to 100%, a poorly fitted N95 mask with gaps offers less protection than a well-fitted surgical/cloth mask with filter layer. We also found that double masking—the wearing of cloth mask on top of a surgical mask—offers little to no additional protection as compared to a single cloth/surgical mask. The results of our work can inform the implementation of mask mandates to minimize airborne transmissions of coronavirus disease of 2019 (COVID-19).

Risk assessment of airborne COVID-19 exposure in social settings.

The COVID-19 pandemic has led to many countries oscillating between various states of lock-down as they seek to balance keeping the economy and essential services running and minimizing the risk of further transmission. Decisions are made about which activities to keep open across a range of social settings and venues guided only by ad hoc heuristics regarding social distancing and personal hygiene. Hence, we propose the dual use of computational fluid dynamic simulations and surrogate aerosol measurements for location-specific assessment of risk of infection across different real-world settings. We propose a 3-tiered risk assessment scheme to facilitate classification of scenarios into risk levels based on simulations and experiments. Threshold values of <54 and >840 viral copies and <5% and >40% of original aerosol concentration are chosen to stratify low, medium, and high risk. This can help prioritize allowable activities and guide implementation of phased lockdowns or re-opening. Using a public bus in Singapore as a case study, we evaluate the relative risk of infection across scenarios such as different activities and passenger positions and demonstrate the effectiveness of our risk assessment methodology as a simple and easily interpretable framework. For example, this study revealed that the bus's air-conditioning greatly influences dispersion and increases the risk of certain seats and that talking can result in similar relative risk to coughing for passengers around an infected person. Both numerical and experimental approaches show similar relative risk levels with a Spearman's correlation coefficient of 0.74 despite differing observables, demonstrating applicability of this risk assessment methodology to other scenarios.

Eye Protection in ENT Practice During the COVID-19 Pandemic.

OBJECTIVES: There is a lack of evidence-based guidelines with regard to eye protection for aerosol-generating procedures in otolaryngology practice. In addition, some recommended personal protective equipment (PPE) is not compatible with commonly used ENT equipment. This study aims to investigate the degree of eye protection that commonly used PPE gives. STUDY DESIGN: Simulation model. SETTING: Simulation laboratory. METHODS: A custom-built setup was utilized to simulate the clinical scenario of a patient cough in proximity of a health care worker. A system that sprays a xanthan-fluorescein mixture was set up and calibrated to simulate a human cough. A mannequin with cellulose paper placed on its forehead, eyes, and mouth was fitted with various PPE combinations and exposed to the simulated cough. The degree of contamination on the cellulose papers was quantified with a fluorescent microscope able to detect aerosols ≥10 µm. RESULTS: When no eye protection was worn, 278 droplets/aerosols reached the eye area. The use of the surgical mask with an attached upward-facing shield alone resulted in only 2 droplets/aerosols reaching the eye area. In this experiment, safety glasses and goggles performed equally, as the addition of either brought the number of droplets/aerosols reaching the eye down to 0. CONCLUSION: When used with an upward-facing face shield, there was no difference in the eye protection rendered by safety goggles or glasses in this study. Safety glasses may be considered a viable alternative to safety goggles in aerosol-generating procedures.

Effective design of barrier enclosure to contain aerosol emissions from COVID-19 patients.

Facing shortages of personal protective equipment, some clinicians have advocated the use of barrier enclosures (typically mounted over the head, with and without suction) to contain aerosol emissions from coronavirus disease 2019 (COVID-19) patients. There is, however, little evidence for its usefulness. To test the effectiveness of such a device, we built a manikin that can expire micron-sized aerosols at flow rates close to physiological conditions. We then placed the manikin inside the enclosure and used a laser sheet to visualize the aerosol leaking out. We show that with sufficient suction, it is possible to effectively contain aerosol from the manikin, reducing aerosol exposure outside the enclosure by 99%. In contrast, a passive barrier without suction only reduces aerosol exposure by 60%.

The Efficacy of Plant-Based Ionizers in Removing Aerosol for COVID-19 Mitigation.

Small-sized droplets/aerosol transmission is one of the factors responsible for the spread of COVID-19, in addition to large droplets and surface contamination (fomites). While large droplets and surface contamination can be relatively easier to deal with (i.e., using mask and proper hygiene measures), aerosol presents a different challenge due to their ability to remain airborne for a long time. This calls for mitigation solutions that can rapidly eliminate the airborne aerosol. Pre-COVID-19, air ionizers have been touted as effective tools to eliminate small particulates. In this work, we sought to evaluate the efficacy of a novel plant-based ionizer in eliminating aerosol. It was found that factors such as the ion concentration, humidity, and ventilation can drastically affect the efficacy of aerosol removal. The aerosol removal rate was quantified in terms of ACH (air changes per hour) and CADR- (clean air delivery rate-) equivalent unit, with ACH as high as 12 and CADR as high as 141 ft3/minute being achieved by a plant-based ionizer in a small isolated room. This work provides an important and timely guidance on the effective deployment of ionizers in minimizing the risk of COVID-19 spread via airborne aerosol, especially in a poorly-ventilated environment.

Respiratory droplet generation and dispersal during nasoendoscopy and upper respiratory swab testing.

Respiratory particle generation and dispersal during nasoendoscopy and swab testing is studied with high-speed video and laser light illumination. Video analysis reveals droplet formation in three manoeuvres during nasoendoscopy - sneezing, vocalization, and nasal decongestion spray. A capillary bridge of mucus can be seen when a nasoendoscope exits wet nares. No droplet formation is seen during oral and nasopharyngeal swab testing. We outline the following recommendations: pull the face mask down partially and keep the mouth covered, only allowing nasal access during nasoendoscopy; avoid nasal sprays if possible; if nasal sprays are used, procedurists should be in full personal protective equipment prior to using the spray; withdrawal of swabs and scopes should be performed in a slow and controlled fashion to reduce potential dispersion of droplets when the capillary bridge of mucus breaks up.