Post by Admin on Nov 30, 2020 0:11:22 GMT
V. EFFECTIVENESS OF FACEMASKS FOR PREVENTION OF VIRUS TRANSMISSION
The current studies recognized the airborne transmission of aerosols produced by asymptomatic individuals during speaking and breathing as a key factor, leading to the spread of infectious respiratory diseases such as COVID-19.62,80–82 However, the spread of these airborne diseases has been successfully controlled up to a certain extent by using the facemasks.11,19,49,83–85 In the ongoing global pandemic of the COVID-19, where vaccine development is still at a phase of the trial stage, the respiratory protective equipment such as facemasks has proven to be a complementary countermeasure against the spread of the novel coronavirus. In this regard, several researchers have performed theoretical and experimental investigations of virus transmissibility through the facemasks and alternatives. Stutt et al.86 developed the holistic mathematical frameworks for assessing the potential impact of facemasks in COVID-19 pandemic management. The results revealed that professional and home-made facemasks were highly efficacious to reduce exposure to respiratory infections among the public. In addition, when people wear the facemasks all-time at the public places, the certain epidemiological threshold, known as the effective reproduction number, could be decreased below 1, leading to the prevention of epidemic spread. Ngonghala et al.87 developed a parametric model for providing deeper insights into the transmission dynamics and control of COVID-19 in a community. They used the COVID-19 data from New York state and the entire US to assess the population-level impact of various intervention strategies. The results suggested that the consistent use of facemasks could significantly reduce the effective reproduction number. The highly efficacious facemask, such as surgical masks with an estimated efficacy of around 70%, could lead to the eradication of the pandemic if at least 70% of the residents use such masks in public consistently. The use of low efficacy masks, such as cloth masks with an estimated efficacy of 30%, could also lead to a significant reduction of COVID-19 burden. Yan et al.88 evaluated the effectiveness of different respiratory protective equipment in controlling infection rates in an influenza outbreak. They used a previously developed risk assessment model89 to show N95 respirators’ efficacy, low-filtration surgical mask (adult), high-filtration surgical mask (adult), high filtration pediatric mask, and low filtration pediatric mask. The study revealed that donning these masks with a 50% compliance rate resulted in a significant reduction in transmission risk and with 80% compliance rate nearly eradicated the influenza outbreak. Prasanna Simha and Mohan Rao90 quantitatively investigated the distance of travel of typical human coughs with and without different masks: disposable three-ply surgical masks and N95 masks. In their study, the schlieren method, a highly sensitive, non-intrusive flow imagining technique, was used to visualize the human cough flow features. The experimental statistics showed that the propagation of a viscous vortex ring mainly governed cough flow behavior. While wearing regular face masks, the cough droplets traveled approximately half the distance traveled by expelled droplets without a mask. However, N95 was found to be most effective in limiting the spread of cough droplets. Leung et al.91 performed experimental studies to investigate the efficacy of surgical facemasks to prevent respiratory virus shedding. The surgical facemasks’ efficiency was measured against the coronavirus, influenza virus, and rhinovirus of two broad particle sizes, respiratory droplets (≥5 μm) and aerosols (droplet nuclei with aerodynamic diameter ≤5 μm). The results indicated that surgical facemasks could efficaciously prevent the transmission of human coronaviruses and influenza viruses into the environment in respiratory droplets, but no significant reduction in aerosols.
Moreover, the steep rise in demand for medical facemasks during the current pandemic COVID-19 has resulted in a subsequent breakdown of the global supply chain that led to an acute shortage in the market. To mitigate this discontinuous supply chain system, scientists have put much effort into exploring alternative fabrics with sufficient filtering capacity that are readily available and affordable. Kähler and Hain92 performed a detailed analysis of the efficacy of facemasks to prevent virus spread. In the first step, the transmission of droplets released by the mouth when breathing, speaking, and coughing was characterized. Then, the filtering capacity of the various facemasks was analyzed. The experimental results have shown that most household materials tested do not provide much protection against the virus transmission via droplets and, therefore, are unsuitable as materials for protective masks. However, filtering facepiece respirator (FFR) performance-based masks such as FFP2 (Europe EN 149-2001), N95 (United States NIOSH-42CFR84), DS2 (Japan JMHLW-Notification 214, 2018), and KN95 (China GB2626-2006) offer adequate protection as they are only permeable to a tiny fraction of few micrometer-sized droplets. Konda et al.93 evaluated the filtration efficiency of various commonly available fabrics, including cotton, silk, chiffon, flannel, various synthetics, and their combinations, which were used in the fabrication of cloth masks. The filtration performance of these fabrics was conducted by generating the aerosol particles at the cloth sample’s upstream side. The aerosol particulates ranging from ∼10 nm to ∼10 μm scale sizes, particularly relevant for respiratory virus transmission, were produced by using a commercial sodium chloride (NaCl) aerosol generator. In addition, the air with a controlled airflow rate was drawn through the sample using a blower fan. The filtration efficiency ηf of each sample was computed by measuring the particles’ concentration upstream and downstream as ηf=Cu−CdCu×100, where Cu and Cd are the mean particle concentrations per bin upstream and downstream, respectively. Moreover, the pressure drop across the facemasks and the air velocities were measured using a digital manometer and a hot wire anemometer. The experimental investigations revealed that the materials such as natural silk, a chiffon weave (90% polyester–10% Spandex fabric), and flannel (65% cotton–35% polyester blend) provided good electrostatic filtering of particles. In addition, fabric with tighter weaves and low porosity, such as cotton sheets with a high thread count, has resulted in better filtration efficiencies. For instance, a 600 TPI (thread per inch) cotton sheet can provide average filtration efficiencies of 79 ± 23% (in the 10 nm–300 nm range) and 98.4 ± 0.2% (in the 300 nm to 6 µm range). A cotton quilt with batting provides 96% ± 2% (10 nm–300 nm) and 96.1 ± 0.3% (300 nm to 6 µm). Surprisingly, a four-layer silk (e.g., scarf) was found to be effective with an average filtration efficiency of >85% across the 10 nm to 6 µm particle size range. Moreover, the hybrid masks made by combinations of two or more fabric types, leveraging mechanical and electrostatic filtering, could be an effective approach for better filtration [Fig. 4(a)]. Verma et al.46 performed the qualitative investigations for assessing the effectiveness of easily available facemasks such as bandana (elastic T-shirt material, 85 threads/in.), folded handkerchief (cotton, 55 threads/in.), stitched mask (quilting cotton, 70 threads/in.), and other commercial masks. They observed that a stitched mask made of quilting cotton was most effective, followed by the commercial mask, the folded handkerchief, and, finally, the bandana. Their observations also suggested that a higher thread count by itself is not sufficient to provide a better droplet filtration capability. The material types and fabrication techniques have a significant impact on the performance of facemasks. Davies et al.42 examined the efficacy of homemade masks as an alternative to commercial surgical masks.
Various household materials such as 100% cotton T-shirt, scarf, tea towel, pillowcase, antimicrobial pillowcase, vacuum cleaner bag, cotton mix, linen, and silk were evaluated for the capacity to prevent bacterial and viral aerosol transmission. The performance of these household facemasks was compared with the standard surgical mask. The experimental outcomes showed that these homemade masks could reduce the likelihood of infection but are not efficient for the complete elimination of risks. A similar conclusion has been made in a previously published review article by Rossettie et al.94 and Loupa et al.95 Recently, Ho et al.96 investigated the droplet filtration efficiency of the self-designed triple-layer cotton masks, and their performance was compared with the standard medical mask. All tests were performed in two different locations: in a regular bedroom and a car with air conditioning. The particles with a size range of 20 nm–1000 nm were taken into consideration, and the filtration efficiency was measured. Other factors such as environmental conditions (temperature and relative humidity) and cough/sneeze counts per hour were measured for each measurement. The results revealed that cotton and surgical masks could significantly reduce the number of microorganisms expelled by participants with the filtration efficiency of 86.4% and 99.9%, respectively [Fig. 4(b)]. However, the surgical mask was three times more effective in blocking transmission than the cotton mask. In a recent study, Fischer et al.97 performed testing of 14 different facemasks or mask alternatives ranging from the kind worn by healthcare professionals to neck fleeces and knitted masks. Figure 4(c) shows the photographs of the facemasks and alternatives considered in the investigation. A comparison was made on the dispersal of droplets from a mask wearer’s breath while wearing one of the face coverings to the results of a controlled trial where their mouth was fully exposed. The study revealed that some mask types matched standard surgical masks’ performance, while some mask alternatives, such as neck fleece or bandanas, offered little protection against infection [Fig. 4(d)]. Besides, they demonstrated a simple optical measurement method to evaluate the efficacy of facemasks to reduce respiratory droplet transmission during regular speech. Figure 4(e) shows the schematic of the developed setup. The proposed optical system is inexpensive and easy-to-operate, even by non-experts.
FIG. 4. (a) Schematic illustration of the possible filtration mechanism of the hybrid cloth masks. In addition, the plot shows the filtration efficiencies of a surgical mask and hybrid fabric cotton/silk with (dashed) and without a gap (solid). The gap used was ∼1% of the active mask surface area. Reprinted with permission from Konda et al., “Aerosol filtration efficiency of common fabrics used in respiratory cloth masks,” ACS Nano 14, 6339 (2020). Copyright 2020 American Chemical Society. (b) Performance comparison between the medical masks and the three-layer cotton mask. Reproduced with permission from Ho et al., “Medical mask versus cotton mask for preventing respiratory droplet transmission in micro environments,” Sci. Total Environ. 735, 139510 (2020). Copyright 2020 Elsevier B.V. (c) Photographs of the facemasks under investigation: (1) three-layer surgical mask, (2) N95 mask with a exhalation valve “Valved N95,” (3) knitted mask, (4) double-layer polypropylene apron mask “Polyprop,” (5) cotton–polypropylene–cotton mask “Poly/cotton,” (6) single layer Maxima AT mask “MaxAT,” (7) double-layer cotton-pleated style mask “Cotton2,” (8) double-layer cotton mask–Olson style mask “Cotton4,” (9) double-layer cotton-pleated style mask “Cotton3,” (10) single-layer cotton-pleated style mask “Cotton1,” (11) gaiter type neck fleece “Fleece,” (12) double-layer bandana “Bandana,” (13) single-layer cotton-pleated style mask “Cotton5,” and (14) N95 mask no exhalation valve fitted “Fitted N95.” (d) Relative droplet transmission through the corresponding facemasks. (e) Schematic of the experimental optical setup. Reproduced with permission from Fischer et al., “Low-cost measurement of face mask efficacy for filtering expelled droplets during speech,” Sci. Adv. 6, eabd3083 (2020). Copyright 2015 Author(s), licensed under a Creative Commons Attribution 4.0 License.
Furthermore, the use of face shields has widely been used along with standard face masks. Face shields are generally made of transparent plastic sheets. They offer several advantages as follows: comfortable to wear, easy-to-clean, clear conversations between the speakers with visible facial expressions, and reduce autoinoculation by preventing the wearer from touching their face.98In addition, face shields prevent the user’s face from the direct contact of liquid droplets. More recently, Verma et al.99 investigated the effectiveness of the face shields and exhalation valves in the respiratory droplet transport context. They performed experimentation in an emulated coughing and sneezing environment for a qualitative visualization analysis. The results indicated that although face shields block the initial forward motion of the fluid jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on environmental conditions. In addition, for the facemasks equipped with an exhalation port, the droplets pass through the exhalation valves. Based on the observations, they opined that high-quality cloth or surgical masks perform better than the face shields and exhalation valves.
The current studies recognized the airborne transmission of aerosols produced by asymptomatic individuals during speaking and breathing as a key factor, leading to the spread of infectious respiratory diseases such as COVID-19.62,80–82 However, the spread of these airborne diseases has been successfully controlled up to a certain extent by using the facemasks.11,19,49,83–85 In the ongoing global pandemic of the COVID-19, where vaccine development is still at a phase of the trial stage, the respiratory protective equipment such as facemasks has proven to be a complementary countermeasure against the spread of the novel coronavirus. In this regard, several researchers have performed theoretical and experimental investigations of virus transmissibility through the facemasks and alternatives. Stutt et al.86 developed the holistic mathematical frameworks for assessing the potential impact of facemasks in COVID-19 pandemic management. The results revealed that professional and home-made facemasks were highly efficacious to reduce exposure to respiratory infections among the public. In addition, when people wear the facemasks all-time at the public places, the certain epidemiological threshold, known as the effective reproduction number, could be decreased below 1, leading to the prevention of epidemic spread. Ngonghala et al.87 developed a parametric model for providing deeper insights into the transmission dynamics and control of COVID-19 in a community. They used the COVID-19 data from New York state and the entire US to assess the population-level impact of various intervention strategies. The results suggested that the consistent use of facemasks could significantly reduce the effective reproduction number. The highly efficacious facemask, such as surgical masks with an estimated efficacy of around 70%, could lead to the eradication of the pandemic if at least 70% of the residents use such masks in public consistently. The use of low efficacy masks, such as cloth masks with an estimated efficacy of 30%, could also lead to a significant reduction of COVID-19 burden. Yan et al.88 evaluated the effectiveness of different respiratory protective equipment in controlling infection rates in an influenza outbreak. They used a previously developed risk assessment model89 to show N95 respirators’ efficacy, low-filtration surgical mask (adult), high-filtration surgical mask (adult), high filtration pediatric mask, and low filtration pediatric mask. The study revealed that donning these masks with a 50% compliance rate resulted in a significant reduction in transmission risk and with 80% compliance rate nearly eradicated the influenza outbreak. Prasanna Simha and Mohan Rao90 quantitatively investigated the distance of travel of typical human coughs with and without different masks: disposable three-ply surgical masks and N95 masks. In their study, the schlieren method, a highly sensitive, non-intrusive flow imagining technique, was used to visualize the human cough flow features. The experimental statistics showed that the propagation of a viscous vortex ring mainly governed cough flow behavior. While wearing regular face masks, the cough droplets traveled approximately half the distance traveled by expelled droplets without a mask. However, N95 was found to be most effective in limiting the spread of cough droplets. Leung et al.91 performed experimental studies to investigate the efficacy of surgical facemasks to prevent respiratory virus shedding. The surgical facemasks’ efficiency was measured against the coronavirus, influenza virus, and rhinovirus of two broad particle sizes, respiratory droplets (≥5 μm) and aerosols (droplet nuclei with aerodynamic diameter ≤5 μm). The results indicated that surgical facemasks could efficaciously prevent the transmission of human coronaviruses and influenza viruses into the environment in respiratory droplets, but no significant reduction in aerosols.
Moreover, the steep rise in demand for medical facemasks during the current pandemic COVID-19 has resulted in a subsequent breakdown of the global supply chain that led to an acute shortage in the market. To mitigate this discontinuous supply chain system, scientists have put much effort into exploring alternative fabrics with sufficient filtering capacity that are readily available and affordable. Kähler and Hain92 performed a detailed analysis of the efficacy of facemasks to prevent virus spread. In the first step, the transmission of droplets released by the mouth when breathing, speaking, and coughing was characterized. Then, the filtering capacity of the various facemasks was analyzed. The experimental results have shown that most household materials tested do not provide much protection against the virus transmission via droplets and, therefore, are unsuitable as materials for protective masks. However, filtering facepiece respirator (FFR) performance-based masks such as FFP2 (Europe EN 149-2001), N95 (United States NIOSH-42CFR84), DS2 (Japan JMHLW-Notification 214, 2018), and KN95 (China GB2626-2006) offer adequate protection as they are only permeable to a tiny fraction of few micrometer-sized droplets. Konda et al.93 evaluated the filtration efficiency of various commonly available fabrics, including cotton, silk, chiffon, flannel, various synthetics, and their combinations, which were used in the fabrication of cloth masks. The filtration performance of these fabrics was conducted by generating the aerosol particles at the cloth sample’s upstream side. The aerosol particulates ranging from ∼10 nm to ∼10 μm scale sizes, particularly relevant for respiratory virus transmission, were produced by using a commercial sodium chloride (NaCl) aerosol generator. In addition, the air with a controlled airflow rate was drawn through the sample using a blower fan. The filtration efficiency ηf of each sample was computed by measuring the particles’ concentration upstream and downstream as ηf=Cu−CdCu×100, where Cu and Cd are the mean particle concentrations per bin upstream and downstream, respectively. Moreover, the pressure drop across the facemasks and the air velocities were measured using a digital manometer and a hot wire anemometer. The experimental investigations revealed that the materials such as natural silk, a chiffon weave (90% polyester–10% Spandex fabric), and flannel (65% cotton–35% polyester blend) provided good electrostatic filtering of particles. In addition, fabric with tighter weaves and low porosity, such as cotton sheets with a high thread count, has resulted in better filtration efficiencies. For instance, a 600 TPI (thread per inch) cotton sheet can provide average filtration efficiencies of 79 ± 23% (in the 10 nm–300 nm range) and 98.4 ± 0.2% (in the 300 nm to 6 µm range). A cotton quilt with batting provides 96% ± 2% (10 nm–300 nm) and 96.1 ± 0.3% (300 nm to 6 µm). Surprisingly, a four-layer silk (e.g., scarf) was found to be effective with an average filtration efficiency of >85% across the 10 nm to 6 µm particle size range. Moreover, the hybrid masks made by combinations of two or more fabric types, leveraging mechanical and electrostatic filtering, could be an effective approach for better filtration [Fig. 4(a)]. Verma et al.46 performed the qualitative investigations for assessing the effectiveness of easily available facemasks such as bandana (elastic T-shirt material, 85 threads/in.), folded handkerchief (cotton, 55 threads/in.), stitched mask (quilting cotton, 70 threads/in.), and other commercial masks. They observed that a stitched mask made of quilting cotton was most effective, followed by the commercial mask, the folded handkerchief, and, finally, the bandana. Their observations also suggested that a higher thread count by itself is not sufficient to provide a better droplet filtration capability. The material types and fabrication techniques have a significant impact on the performance of facemasks. Davies et al.42 examined the efficacy of homemade masks as an alternative to commercial surgical masks.
Various household materials such as 100% cotton T-shirt, scarf, tea towel, pillowcase, antimicrobial pillowcase, vacuum cleaner bag, cotton mix, linen, and silk were evaluated for the capacity to prevent bacterial and viral aerosol transmission. The performance of these household facemasks was compared with the standard surgical mask. The experimental outcomes showed that these homemade masks could reduce the likelihood of infection but are not efficient for the complete elimination of risks. A similar conclusion has been made in a previously published review article by Rossettie et al.94 and Loupa et al.95 Recently, Ho et al.96 investigated the droplet filtration efficiency of the self-designed triple-layer cotton masks, and their performance was compared with the standard medical mask. All tests were performed in two different locations: in a regular bedroom and a car with air conditioning. The particles with a size range of 20 nm–1000 nm were taken into consideration, and the filtration efficiency was measured. Other factors such as environmental conditions (temperature and relative humidity) and cough/sneeze counts per hour were measured for each measurement. The results revealed that cotton and surgical masks could significantly reduce the number of microorganisms expelled by participants with the filtration efficiency of 86.4% and 99.9%, respectively [Fig. 4(b)]. However, the surgical mask was three times more effective in blocking transmission than the cotton mask. In a recent study, Fischer et al.97 performed testing of 14 different facemasks or mask alternatives ranging from the kind worn by healthcare professionals to neck fleeces and knitted masks. Figure 4(c) shows the photographs of the facemasks and alternatives considered in the investigation. A comparison was made on the dispersal of droplets from a mask wearer’s breath while wearing one of the face coverings to the results of a controlled trial where their mouth was fully exposed. The study revealed that some mask types matched standard surgical masks’ performance, while some mask alternatives, such as neck fleece or bandanas, offered little protection against infection [Fig. 4(d)]. Besides, they demonstrated a simple optical measurement method to evaluate the efficacy of facemasks to reduce respiratory droplet transmission during regular speech. Figure 4(e) shows the schematic of the developed setup. The proposed optical system is inexpensive and easy-to-operate, even by non-experts.
FIG. 4. (a) Schematic illustration of the possible filtration mechanism of the hybrid cloth masks. In addition, the plot shows the filtration efficiencies of a surgical mask and hybrid fabric cotton/silk with (dashed) and without a gap (solid). The gap used was ∼1% of the active mask surface area. Reprinted with permission from Konda et al., “Aerosol filtration efficiency of common fabrics used in respiratory cloth masks,” ACS Nano 14, 6339 (2020). Copyright 2020 American Chemical Society. (b) Performance comparison between the medical masks and the three-layer cotton mask. Reproduced with permission from Ho et al., “Medical mask versus cotton mask for preventing respiratory droplet transmission in micro environments,” Sci. Total Environ. 735, 139510 (2020). Copyright 2020 Elsevier B.V. (c) Photographs of the facemasks under investigation: (1) three-layer surgical mask, (2) N95 mask with a exhalation valve “Valved N95,” (3) knitted mask, (4) double-layer polypropylene apron mask “Polyprop,” (5) cotton–polypropylene–cotton mask “Poly/cotton,” (6) single layer Maxima AT mask “MaxAT,” (7) double-layer cotton-pleated style mask “Cotton2,” (8) double-layer cotton mask–Olson style mask “Cotton4,” (9) double-layer cotton-pleated style mask “Cotton3,” (10) single-layer cotton-pleated style mask “Cotton1,” (11) gaiter type neck fleece “Fleece,” (12) double-layer bandana “Bandana,” (13) single-layer cotton-pleated style mask “Cotton5,” and (14) N95 mask no exhalation valve fitted “Fitted N95.” (d) Relative droplet transmission through the corresponding facemasks. (e) Schematic of the experimental optical setup. Reproduced with permission from Fischer et al., “Low-cost measurement of face mask efficacy for filtering expelled droplets during speech,” Sci. Adv. 6, eabd3083 (2020). Copyright 2015 Author(s), licensed under a Creative Commons Attribution 4.0 License.
Furthermore, the use of face shields has widely been used along with standard face masks. Face shields are generally made of transparent plastic sheets. They offer several advantages as follows: comfortable to wear, easy-to-clean, clear conversations between the speakers with visible facial expressions, and reduce autoinoculation by preventing the wearer from touching their face.98In addition, face shields prevent the user’s face from the direct contact of liquid droplets. More recently, Verma et al.99 investigated the effectiveness of the face shields and exhalation valves in the respiratory droplet transport context. They performed experimentation in an emulated coughing and sneezing environment for a qualitative visualization analysis. The results indicated that although face shields block the initial forward motion of the fluid jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on environmental conditions. In addition, for the facemasks equipped with an exhalation port, the droplets pass through the exhalation valves. Based on the observations, they opined that high-quality cloth or surgical masks perform better than the face shields and exhalation valves.