Respiratory virus shedding in exhaled breath and efficacy of face masks
Nancy LeungDaniel K. W. ChuEunice Y. C. ShiuKwok‐Hung ChanJames McDevittBenien J. P. HauHui‐Ling YenYuguo LiDkm IpMalik PeirisWH SetoGM LeungDonald K. MiltonBenjamin J. Cowling
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Keywords:
Coronavirus
Viral Shedding
Face masks
The duration of viral shedding is determined by a balance between de novo infection and removal of infected cells. That is, if infection is completely blocked with antiviral drugs (100% inhibition), the duration of viral shedding is minimal and is determined by the length of virus production. However, some mathematical models predict that if infected individuals are treated with antiviral drugs with efficacy below 100%, viral shedding may last longer than without treatment because further de novo infections are driven by entry of the virus into partially protected, uninfected cells at a slower rate. Using a simple mathematical model, we quantified SARS-CoV-2 infection dynamics in non-human primates and characterized the kinetics of viral shedding. We counterintuitively found that treatments initiated early, such as 0.5 d after virus inoculation, with intermediate to relatively high efficacy (30–70% inhibition of virus replication) yield a prolonged duration of viral shedding (by about 6.0 d) compared with no treatment.
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Infectious dose
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Viral Shedding
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Wearing face masks have been implemented as a public and personal health control measure against the spread of coronavirus disease (COVID-19). However, the protection level of nonmedical face masks, such as women face veils, is still uncertain. This study aimed to assess the filtration efficiency (FE; percentage of particles retained by a mask) of different types of medical masks (either as sealed or unsealed, single or doubled), non-medical masks (cloth masks) and face veils. FE of face masks was evaluated using an in-house 3D-printed air duct connected to the Aerotrak particle counter with a capability of counting particle sizes of 0.3, 0.5, 0.7, 1, 2 and 5 μm. A set of 10 earloop surgical masks,10 tie-on surgical masks, 3 triple-layers reusable cloth masks and 3 types (short, medium and long) of traditional face veils were included in the study. The unsealed surgical masks showed intermediate FE (36.54-80.58%), with no observed differences between tie-on and earloop or single and doubled masks. For each mask type, the mean FE values of sealed surgical masks (FE≥99.16%) was significantly higher (P<0.001) than the unsealed ones (FE≤80.58%). No significant difference was observed in the mean FE values between unsealed surgical masks and either cloth masks (FE=23.19-75.35%, P=0.26) or face veils (FE=19.10- 70.68%, P=0.14). However, a mockup experiment showed that wearing a surgical mask under the face veil significantly improve the FE (33.73-79.18%; P<0.001). We conclude that besides sealed surgical masks that ensure optimal filtration under the experimental conditions, the unsealed surgical and cloth masks and face veils showed comparable performance and acceptable protection at 5 μm particle size, which is the most relevant particle size associated with COVID-19 infectious droplets. Wearing a surgical mask under the face veil significantly improves the FE compared to wearing a face veil alone.
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2019-20 coronavirus outbreak
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COVID-19 is caused by the virus SARS-CoV-2 that belongs to the Coronaviridae groups. The subgroups of the coronavirus families are α , β , γ , and δ coronavirus (the four general human coronaviruses). Representative coronaviruses consist of NL63 coronavirus (human) and porcine transmissible gastroenteritis from the Alphacoronavirus genus; mouse hepatitis coronavirus (MHV), bovine coronavirus (BCoV), severe acute respiratory syndrome coronavirus (SARS-CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV); avian infectious bronchitis virus (IBV); and porcine δ -coronavirus (PdCoV). This work exhibits, δ -coronavirus spikes are fundamentally and evolutionally more similar related to α -coronavirus spikes than to β -coronavirus or γ -coronavirus spikes due to the receptor recognition, membrane fusion phenomenon, and immune evasion behavior.
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The reported median duration of viral shedding after infection with SARS-CoV2 is between 12 and 20 days. It is now established that infected individuals can continue to shed viral ribonucleic acid (RNA) without shedding live virus. This has implications for quarantine and infection control practices. COVID in the acute phase seems to be milder in children, and the duration of viral RNA shedding is shorter in children compared to adults. SARS-CoV-2 infections in the newborn period is rare. Little is known about the duration of viral shedding in preterm infants with vertically acquired SARS-CoV-2. 3 of the 4 preterm infants cared for at our center had prolonged shedding up to 34 days with live viral shedding not seen beyond the second week when tested in 3 of them.
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2019-20 coronavirus outbreak
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Previous field and experimental studies have demonstrated that heterosubtypic immunity (HSI) is a potential driver of Influenza A virus (IAV) prevalence and subtype diversity in mallards. Prior infection with IAV can reduce viral shedding during subsequent reinfection with IAV that have genetically related hemagglutinins (HA). In this experiment, we evaluated the effect of HSI conferred by an H3N8 IAV infection against increasing challenge doses of closely (H4N6) and distantly (H6N2) related IAV subtypes in mallards. Two groups of thirty 1-month-old mallards each, were inoculated with 105.9 50% embryo infectious doses (EID50) of an H3N8 virus or a mock-inoculum. One month later, groups of five birds each were challenged with increasing doses of H4N6 or H6N2 virus; age-matched, single infection control ducks were included for all challenges. Results demonstrate that naïve birds were infected after inoculation with 103 and 104 EID50 doses of the H4N6 or H6N2 virus, but not with 102 EID50 doses of either IAV. In contrast, with birds previously infected with H3N8 IAV, only one duck challenged with 104 EID50 of H4N6 IAV was shedding viral RNA at 2 days post-inoculation, and with H6N2 IAV, only birds challenged with the 104 EID50 dose were positive to virus isolation. Viral shedding in ducks infected with H6N2 IAV was reduced on days 2 and 3 post-inoculation compared to control birds. To explain the differences in the dose necessary to produce infection among H3-primed ducks challenged with H4N6 or H6N2 IAV, we mapped the amino acid sequence changes between H3 and H4 or H6 HA on predicted three-dimensional structures. Most of the sequence differences occurred between H3 and H6 at antigenic sites A, B, and D of the HA1 region. These findings demonstrate that the infectious dose necessary to infect mallards with IAV can increase as a result of HSI and that this effect is most pronounced when the HA of the viruses are genetically related.
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The COVID-19 virus, SARS-CoV-2, is thought to transmit mostly by respiratory droplets from coughing or sneezing when people are in close proximity. It is advised to wear a face mask or respirator (N95/KN95) to prevent the spread of COVID-19-causing SARS-CoV-2. Although few studies have examined their real-world efficacy in preventing SARS-CoV-2 infection, well-fitting face masks and respirators efficiently filter virus-sized particles in laboratory settings. Mathematical modelling demonstrates that wearing masks significantly slows the transmission of SARS-CoV-2 and lowers the chance of infection, particularly when paired with other non-medical interventions (such as maintaining a safe social distance). In many studies, it has been discovered that both N95 masks and ordinary masks are effective. This study is aimed at evaluation effectiveness of wearing facial masks at preventing Covid-19 infections.
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Face masks
2019-20 coronavirus outbreak
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With shortages of face masks being reported worldwide, it is critical to consider alternatives to commercially manufactured face masks. This study aimed to test and compare the efficacy of various makes of locally made or homemade cloth face masks obtained from face-mask vendors in Kampala, Uganda, during the COVID-19 pandemic. The testing was performed to assess the bacterial filtration efficiency (BFE), breathability, distance-dependent fitness, and reusability of the locally made or homemade cloth face masks, while considering the most commonly used non-published face-mask decontamination approaches in Uganda. During laboratory experimentation, modified protocols from various face-mask testing organizations were adopted. Ten different face-mask types were experimented upon; each face-mask type was tested four times for every single test, except for the decontamination protocols involving washing where KN95 and surgical face masks were not included. Among the locally made or homemade cloth face masks, the double-layered cloth face masks (described as F) had better BFE and distance-dependent fitness characteristics, they could be reused, and had good breathability, than the other locally made or homemade cloth face masks. Despite these good qualities, the certainty of these face masks protecting wearers against COVID-19 remains subject to viral filtration efficiency testing.
Face masks
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Personal Protective Equipment
2019-20 coronavirus outbreak
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Abstract Introduction There is a growing body of evidence to support the wearing of face masks to reduce spread of infectious respiratory pathogens, including SARS-CoV-2. However, the literature exploring the effectiveness of homemade fabric face masks is still in its infancy. Developing an evidence base is an important step to ensure that public policy is evidence based and truly effective. Methods Two methodologies were used in this study: quantitative fit testing of various face masks to indicate their effectiveness and a survey of 710 US residents about their perceptions of face mask effectiveness. N95, surgical and two fabric face masks were tested on an individual twenty five times each using a TSI 8038+ machine. Our survey was distributed by Qualtrics XM, asking participants to estimate the effectiveness of N95, surgical and fabric face masks. Results and Discussion Our results indicate that fabric face masks blocked between 62.6% and 87.1% of fine particles, whereas surgical masks protected against an average of 78.2% of fine particles. N95 masks blocked 99.6% of fine particles. Survey respondents tended to underestimate the effectiveness of masks, especially fabric masks. Together these results suggest that fabric masks may be a useful tool in the battle against the COVID-19 pandemic and that increasing public awareness of the effectiveness of fabric masks may help in this endeavour.
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2019-20 coronavirus outbreak
Pandemic
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Abstract Background The spread of COVID-19 has put inpatients lives at risk and increased stress on hospital. Simple, cost effective measures such as mask wearing and hand hygiene have been shown to reduce the spread of droplet borne viruses. Compliance with these measures is variable and when performed improperly, reduce efficacy. Objective In this paper we aim to determine whether the provision of masks at hospital entrances and the use of volunteers to ensure correct mask wearing and hand hygiene can improve compliance with infection prevention measures for COVID-19. Method Visitor and staff compliance with mask wearing and hand hygiene measures were observed with and without the presence of masks and volunteers at hospital entrances at a District General Hospital. Results A total of 519 people were observed entering the hospital. Mask wearing went from 71% to 99% (P = <0.001) with the addition of volunteers. Provision of masks increased mask wearing from 56% to 97% (P = <0.001). Hand hygiene was improved from 9% to 84% (P = <0.001) with the presence of volunteers. Discussion A statistically significant improvement in hand hygiene and correct mask wearing was seen with both the presence of volunteers at hospital entrances and with the provision of masks. This is a relatively small study with heterogenous cohorts of staff and visitors. However, these results appear to indicate that use of volunteers and provision of masks at entrances may improve the compliance with the measures that been shown to reduce the in-hospital transmission of COVID-19.
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