Textile Masks and Surface Covers - A 'Universal Droplet Reduction Model' Against Respiratory Pandemics

The main form of COVID-19 transmission is via oral-respiratory droplet contamination (droplet; very small drop of liquid) produced when individuals talk, sneeze or cough. In hospitals, health-care workers wear facemasks as a minimum medical droplet precaution to protect themselves. Due to the shortage of masks during the pandemic, priority is given to hospitals for their distribution. As a result, the availability/use of medical masks is discouraged for the public. However, given that asymptomatic individuals, not wearing masks within the public, can be highly contagious for COVID-19, prevention of environmental droplet contamination (EnDC) from coughing/sneezing/speech is fundamental to reducing transmission. As an immediate solution to promote public droplet safety, we assessed household textiles to quantify their potential as effective environmental droplet barriers (EDBs). The synchronized implementation of a universal community droplet reduction solution is discussed as a model against COVID-19. Using a bacterial-suspension spray simulation model of droplet ejection (mimicking a sneeze), we quantified the extent by which widely available clothing fabrics reduce the dispersion of droplets onto surfaces within 1.8m, the minimum distance recommended for COVID-19 social distancing. All textiles reduced the number of droplets reaching surfaces, restricting their dispersion to <30cm, when used as single layers. When used as double-layers, textiles were as effective as medical mask/surgical-cloth materials, reducing droplet dispersion to <10cm, and the area of circumferential contamination to ~0.3%. The synchronized implementation of EDBs as a community droplet reduction solution (i.e., face covers/scarfs/masks & surface covers) could reduce EnDC and the risk of transmitting or acquiring infectious respiratory pathogens, including COVID-19.


INTRODUCTION
lactis, Streptococcus diacetylactis, and Saccharomyces florentinus, 75ml; 3x10 6-7 cfu/ml) in 1000ml 79 PBS (Fisher BP-399-1) to simulate a cloud of droplets produced by a sneeze. Probiotics are BSL-80 1/'Generally Recognized As Safe' by the FDA and all experiments were conducted in BSL-2 81 HEPA-filtered microbiology laboratories. No animal/human subjects were used for 82 experimentation. Before testing, spray bottle nozzles were adjusted to produce cloud and jet-83 propelled droplets that match the visual architecture of droplet formation described by Bourouiba el 84 at. 23 . Quantification of droplets landing over a surface was performed at the time of spray using 85 seven 10mm-Petri dishes containing tryptic soy agar (56.75cm 2 surface area/dish) with 5% 86 defibrinated sheep blood, placed on a need droplets to facilitate their expulsion, transmission and EnDC 12 , we first validated a rapid 116 spray-simulation model of droplets (mimicking a sneeze) using a bacterial-suspension to quantify 117 the extent by which widely-available household textiles reduced the ejection/long-distance flight of 118 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.04.07.20045617 doi: medRxiv preprint droplets. To facilitate the enumeration of macro-droplets and invisible micro-droplets, spray-119 simulations were conducted over nutritious-media agar surfaces, incubated for 24h to enable 120 colony-forming-droplet-unit (CFDU) formation. 121 Based on simulations conducted in two institutions, a cloud of bacteria-carrying droplets 122 travel distances reaching >180cm, particularly for large droplets (Figure 1A), consistent with 123 reported dynamics during sneezing 23 . Of relevance to sneezing behavior, simulations illustrate that 124 upward inclination of the central-spray angle allows macro-droplets to reach longer distances 125 (simulation 4/dispersion equations; Figure 1B-E). Although macro-droplets frequently reached 126 180cm, most micro-droplets landed on surfaces within 120cm, with spray air-turbulence carrying 127 micro-droplets into areas not reached due to gravity alone. Thus, social distancing of 1.8m, without 128 EDB-mask protection, as currently recommended, is insufficient to prevent droplet exposure, 129 particularly where essential-service workers congregate during pandemics (transportation, 130 supermarkets/food displays). Therein, wearing EDB-masks together with inclining downward the 131 head/body during sneezing could minimize the spatial range of EnDC.

133
Household textiles retain liquid droplets, particularly if double layered 134 To quantify the droplet retention potential of textiles as EDBs, we next used the same 135 bacterial-spray-simulation model to quantify non-visualizable micro-droplets that could 136 cross/escape the textile-EDB and cause microbial-surface agar contamination (textile/thread details 137 in Remarkably, spray experiments with 'two-layers' (of 100%-combed cotton, common in t-144 shirts; and 100% polyester, in sports jerseys) completely prevented the ejection of large macro-145 droplets (100% EnDC prevention), and drastically reduced the ejection of micro-droplets by a 146 factor of 5.16Log2, which is equivalent to a 97.2% droplet reduction (P<0.020 vs. single-layers, 147 Figure 2C and Supplementary Figures 4-5). Importantly, the least-effective textile as single-layer 148 (most-'breathable', 100%-cotton homespun-115 material) achieved a 90-99.998% droplet retention 149 improvement when used as two-layers (95%CI=3.74-15.39Log2). Lastly, all textiles were equally 150 effective at absorbing the humidity from 3-sprays compared to medical mask/surgical cloth 151 materials, which condensate after 1-spray ( Figure 2D). Together, experiments indicate that two-152 layers of household textiles are as effective as medical masks preventing EnDC, and that more 153 breathable materials in ≥2-layers could be effectively used if individuals deem two-layer, 'denser' 154 textiles too air-restrictive. 155 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
is the (which was not peer-reviewed) The copyright holder for this preprint increase daily, and the fabrication of EDB by centralized organizations could take weeks to reach 167 entire 'lockdown' communities, we suggest, based on the cotton/polyester EnDC effectiveness, and 168 a homemade EDB-mask fabrication trial (Supplementary Figure 6), that, from one piece of 169 clothing, every individual could make (without sewing machine) two 2-layer-EDB masks as an 170 immediate, synchronized contribution to reduce COVID-19 EnDC.

171
From a surface perspective, if everyone were encouraged to wear EDBs, the collective area 172 contaminated with droplets would be miniaturized to 0.3-2.77% (two-layers/single-layers), 173 compared to the potential contamination within 180cm (10.2 m 2 ). Even suboptimal EDBs, effective 174 for 90cm radius, could mathematically reduce the EnDC area by 75.1% (Figure 2E). Our findings 175 and surface estimations are conservative as they are based on simulations using a (non-viscous) 176 liquid solution, assuming stationary individuals. However, the impact of EDB is predictably greater 177 since real/large viscous secretions (Figure 3A), which also travel long distances (>180cm) 23 would 178 be easier to contain by EDB, as communities mobilize. To further lower the risk of fomite 179 (plastic/metal surface) transmission from/by non-EDB-wearers, EDB-textiles used as covers, when 180 relevant, could reduce EnDC by 90-98% (T-test P=0.003, Figure 3B). 181 Finally, to illustrate, in volumetric terms, that EDBs are even more effective preventing 182 EnDC, we conducted a scoping review of literature to conduct analyses of droplet fluid-carrying 183 capacity. Although published droplet sizes vary with study method (Supplementary will also prevent small-size droplet aerosolization by trapping such droplets immediately after 192 production. An overview of a 'universal textile droplet reduction action-model' against pandemics 193 is illustrated in Figure 3C.

195
. CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

196
Despite widespread dissemination of information to curtail the rapid spread of COVID-19 197 outside of China (which affects 20-54-year-old adults, 40% of hospitalizations in the USA 27 ), little 198 attention has been devoted to EnDC and prevention strategies for droplet movement from infected 199 to non-infected individuals within the same community. More concerningly, is that following 200 mandatory 'stay-in-home' quarantine orders, people may return to work unprotected, unaware if 201 they are infected/shedders. This is particularly critical for 'essential pandemic workers', who face 202 different levels of risk (health-care vs. electric/transport/food services), and who can contaminate 203 environmental surfaces as they transit through the community between work (i.e., hospitals) and 204 home, or within their households 28 , without wearing masks. Because mass testing is not always 205 possible 6 , especially for novel organisms like COVID-19, there are growing concerns that 206 asymptomatic and mildly symptomatic citizens will continue to spread and reintroduce the virus to 207 new areas, creating waves of cases, contributing to further economic burden from the outbreak 29 . 208 Nonpharmaceutical interventions (NPIs), also known as community mitigation strategies, 209 are actions that individuals and communities can take in order to slow the spread of illnesses. For 210 pandemics, when medical approaches (hospitalization/treatments) are limited, NPIs are a critical 211 component to achieve resolution. Although PPE, including masks, are scientifically-effective to 212 prevent infectious disease transmission, the use of masks for the general public has not been 213 encouraged by governments 5,7 , possibly because demand will deepen the current crisis of mask 214 unavailability for medical staff, or alternatively, because the use of masks to prevent respiratory 215 infections has been misleadingly deemed ineffective, despite earlier clinical studies indicating that 216 masks could be beneficial in households during pandemics 28,30,31 . 217 Although masks have been extensively studied to determine whether individuals are 218 clinically protected from infections 32,33 , and to confirm that wearing a mask promotes desirable 219 hygiene practices (handwashing, 'avoiding crowds') 5,31,34 , masks have not been examined for their 220 potential to prevent environmental contamination. Masks work, if worn properly; however, 221 individuals (~50%) often fail to wear masks regularly, and properly 30,35 . Despite low compliance, 222 meta-analyses indicate that masks lower the odds of having (SARS)-respiratory infections by 87% 223 (OR=0.13), compared to the odds of having an infection 'not wearing a mask' 36 . 224 Herein, we propose, that in addition to seeking the classical/clinical 'prevention of 225 infection', NPIs could be universally based on 'droplet reduction models' such as EDB to mitigate 226 EnDC. Not only for the prevention of respiratory diseases, but also to prevent widespread 227 environmental dispersion of the virus, which could reach water sources or affect domestic animals, 228 as has been shown for other viruses, including pandemic influenza 37 . 229 The world is in short supply of masks since the international 'lockdown' affected 230 production 38 , with health-care workers experiencing high morbidity/mortality due to reduced 231 protection 39 . Governments are seeking private support to increase mask supplies; however, such 232 strategy could take weeks/months, and infection rates would not improve if supplies were still not 233 available to 'lockdown' communities. Increased community transmission leads to higher demand 234 for medical services, unless transmission is halted. Using household textiles is a potentially life-235 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
is the (which was not peer-reviewed) The copyright holder for this preprint  CFDUs on agar plates illustrating ability of cloud micro-droplets to move around spaces driven by 267 cloud turbulence (left images, agar plates were partially covered with lid at moment of spray), 268 concurrent contamination with macro-and micro-droplets. E) Number of CFDU/plate (56.75 cm 2 ) 269 for 6 simulations over distance. 270 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity. EDBs in reducing circumferential EnDC. 282 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.  . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.