key: cord-0898983-2aahicu5 authors: Stephenson, T. B.; Cumberland, C.; Kibble, G.; Church, C.; Nogueira-Prewitt, S.; MacNamara, S.; Harnish, D. A.; Heimbuch, B. K. title: Evaluation of Facial Protection Against Close-Contact Droplet Transmission date: 2021-02-15 journal: nan DOI: 10.1101/2021.02.09.21251443 sha: d61a18e457c7194ddd0cb0b8b7a2df9c52e6bbfe doc_id: 898983 cord_uid: 2aahicu5 BackgroundFace shields are used as an alternative to facemasks, but their effectiveness in mitigating the spread of SARS-CoV-2 is unclear. The goal of this study is to compare the performance of face shields, surgical facemasks, and cloth facemasks for mitigation of droplet transmission during close contact conditions. MethodsA novel test system was developed to simulate droplet transmission during close contact conditions using two breathing headforms (transmitter and receiver) placed 4 feet apart with one producing droplets containing a DNA marker. Sampling coupons were placed throughout the test setup and subsequently analyzed for presence of DNA marker using quantitative PCR. ResultsAll PPE donned on the transmitter headform provided a significant reduction in transmission of DNA marker to the receiver headform: cloth facemask (78.5%), surgical facemask (89.4%), and face shield (96.1%). All PPE resulted in increased contamination of the eye region of the transmitter headform (9,525.4% average for facemasks and 765.8% for the face shield). Only the face shield increased contamination of the neck region (207.4%), with the cloth facemask and surgical facemask resulting in reductions of 85.9% and 90.2%, respectively. ConclusionsThis study demonstrates face shields can provide similar levels of protection against direct droplet exposure compared to surgical and cloth masks. However, all PPE tested resulted in release of particles that contaminated surfaces. Contamination caused by deflection of the users exhalation prompts concerns for contact transmission via surfaces in exhalation flow path (e.g., face, eyeglasses, etc.). The COVID-19 pandemic has elevated attention for facial protection to a level previously unseen 45 in the United States. American workers in many occupational settings are required to wear face 46 coverings to mitigate virus transmission by asymptomatic and pre-symptomatic individuals. 47 SARS-CoV-2, the causative agent for COVID-19, is primarily transmitted via respiratory 48 droplets. 1 While the Centers for Disease Control and Prevention (CDC) has provided guidance 49 that facemasks are effective for source control and droplet protection, 2 the utility of face shields 50 is still in question. 3 51 Studies to assess the effectiveness of different types of face coverings tend to focus on cough or 52 sneeze simulations that produce high velocity droplets and obtain measurements close to the 53 mask after a short duration. 4, 5, 6 Such simulated coughing studies have demonstrated face shields 54 can reduce user exposure to droplets by 96%, but do not contain all aerosols expelled by the 55 user. 7,8 However, it remains unclear how face shields and other types of face coverings perform 56 under normal respiration conditions, which better represent asymptomatic/pre-symptomatic 57 spreaders of SARS-CoV-2. In these cases, transmission can occur via droplets produced through 58 normal respiration and/or conversation during close contact conditions, which the CDC defines 59 as exposure to a symptomatic, asymptomatic, or pre-symptomatic carrier at a distance of less 60 than 6 feet for at least 15 minutes over a 24 hour period. 9 Thus, it is critical to simulate close 61 5 respiratory secretions has been studied for almost 80 years, the results of these studies are wide-66 ranging and can be influenced by a number of factors. 10, 11 Peer-reviewed literature generally 67 supports a droplet size distribution for respiratory secretions ranging from 10 -100 µm in 68 size. 12, 13 The number of droplets produced during respiration is another critical factor. Xie et al. 69 quantifies total droplet mass output to be ~0.08 g when speaking for ~1 minute, which would 70 yield approximately 1.2 g over 15 minutes. 12 71 The objective of this study was to assess the performance of three types of PPE -cloth facemask, 72 surgical facemask, and face shield -for their ability to mitigate droplet transmission during close 73 contact transmission conditions as defined by the CDC. The intended droplet size distribution 74 will range from 10 -100 µm in size and volume output will target 0.08 g/min during low work 75 rate respiratory conditions. The results of this study will be used to inform the general public 76 regarding effectiveness of different PPE types against droplet transmission. 77 Three types of PPE were evaluated during this study: cloth facemasks (RN15763, Hanes, 80 Winston-Salem, NC); surgical facemasks (B087YPTXT3, Alertcare, San Francisco, CA); and 81 face shields (PPE USA, Hunt Valley, MD). 82 The experimental setup consisted of two ISO Medium 3D-printed plastic headforms, 14 with one 84 headform producing droplets (transmitter) expelled towards the other headform (receiver) to 85 simulate droplet transmission (Figure 1) . Each headform has a 1-in orifice at the mouth through 86 which breathing occurred. The transmitter headform was connected to a breathing machine 87 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. ; https://doi.org/10.1101/2021.02.09.21251443 doi: medRxiv preprint λ -111 was purified using a DNA Clean and Concentrator-100 kit 106 (D4029, Zymogen) and the identity of the DNA fragment was confirmed using gel 107 electrophoresis. DNA concentration was determined using a Synergy LX multi-mode plate 108 reader with a Take3 plate (Biotek, Winooski, VT). 109 For all tests, no PPE was donned onto the receiver headform. Three replicates were performed 122 for each condition. 123 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. A mucin solution (0.3%) was prepared using deionized ultra-filtered water and subsequently 128 steam sterilized. The sterile mucin solution was cooled to room temperature and inoculated with 129 a DNA marker at a concentration of ~1 ng/mL and transferred into the pressure tank. Once the 130 breathing machines reached their respective breathing rates, the valve on the pressure tank was 131 opened to initiate droplet production. Droplets were produced for 15 minutes, then the pressure 132 tank valve was closed, and both breathing machines were turned off. Coupons were collected 133 into sterile 1.5-mL microcentrifuge tubes using sterile forceps and subsequently extracted into 1 134 mL of IDTE (11-01-02-05; Integrated DNA Technologies). A 1-mL sample of residual mucin 135 solution was also collected from the spray chamber. Coupon samples were vortexed vigorously 136 for 5 seconds and mixed gently on the orbital rocker for 1 hour before being stored at 4 . 137 tly ith he as re ed 1 in sly All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The presence of λ -111 DNA was analyzed from 5 µL of each sample using a TaqMan-based 139 absolute qPCR assay with a previously published primer-probe set. 16 duplicates with a variance greater than 1 C q were excluded from further analysis and repeated 153 until a lower variance was achieved. 154 A single qPCR reaction included either 5 µL of a sample or 1 µL of a standard, and all reactions 155 included 1 µL of PhiX174 DNA at 10 2 copies/µL to serve as the exogenous positive control. A 156 negative control consisting of an unused coupon extracted into 1 mL IDTE was included in every 157 experiment. A no-template control (NTC) assembled with IDTE was included in every 96-well 158 plate. The quantity of λ -111 DNA copies was estimated for each reaction using AriaMX 159 software. Reactions with C q values greater than or equal to the negative control were assumed to 160 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Samples that were below detection limit (BDL) were assigned half the detection limit (100 DNA 167 copies). 18 For statistical analysis, one-way ANOVA tests with Tukey's post-test using non-log 168 values were performed through Prism 9 (GraphPad; LaJolla, CA). 169 The droplet size across all three control runs ranged from 0.1 -200 µm with a median diameter 171 of ~27 µm (Figure 3 ). Over 90% of droplets by volume ranged from 10 -100 µm. The droplet 172 mass output over the course of each run was estimated to be ~1.2 g based on the volume output 173 from the Spraytec droplet sizer data. The system only released droplets during exhalation and not 174 during inhalation (data not shown). The mean DNA marker concentration sampled from the spray chamber was 6.46 ± 0.31 log 10 (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. An increase in contamination was observed on the transmitter headform for all three PPE types, 203 but in varying locations. Both the cloth facemasks and surgical facemasks resulted in 204 significantly higher contamination of the transmitter's eye region relative to the control (p < 205 0.0001, p = 0.007, respectively) and relative to the face shield (p = 0.0001 and p = 0.001, 206 respectively). Higher contamination of the eye region was also observed with the face shield 207 when compared to the control, but was not statistically significant (p = 0.34). Higher 208 contamination of the transmitter's forehead was observed for both facemasks, but the face shield 209 resulted in lower contamination compared to the control; no statistically significant differences 210 observed. 211 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. Another trend for all three face coverings evaluated in this study is contamination detected on the 253 transmitter headform during PPE use. With the face shield, higher contamination of all exposed 254 surfaces of the transmitter headform (i.e., eyes, cheek bones, neck) was observed compared to 255 the control, except for the forehead which is covered by a tight-fitting foam piece of the face 256 shield. For both facemasks, higher contamination of the forehead and eyes of the transmitter 257 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. informative results for public health measures. For this study, the simulation of droplet 279 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The focus of this study was to evaluate the effectiveness of PPE at mitigating the spread of 282 respiratory droplets when simulating the CDC close contact condition: a minimum of 15 minutes 283 of contact at less than 6 feet. All PPE tested were shown to be similarly effective at reducing 284 droplet transmission up to 4 feet directly in front of the source, but were also shown to cause 285 self-contamination. Variation in the location and severity of self-contamination observed 286 suggests devices with differences in fit and form will likely result in different areas of the face 287 being contaminated. However, the data from this study supports significant facial contamination 288 should be expected with any PPE that does not provide a tight seal around the mouth and nose of 289 the user. These findings have considerable implications for infection control procedures, drawing 290 attention to the user's face and nearby surfaces as potential sources of contact transmission when 291 using such devices. 292 We would like to thank the Occupational Safety and Health Administration (OSHA) for funding 294 this research under Prime contract #1605DC 19 A 0010. We would also like to thank the Air 295 Force Civil Engineering Center (AFCEC) for providing a breathing machine for the study. We 296 want to thank Mr. Mike McDonald for assistance setting up the test system. 297 Reference 298 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted February 12, 2021. ; https://doi.org/10.1101/2021.02.09.21251443 doi: medRxiv preprint The numbers and the sites of origin of the droplets expelled during expiratory activities The size and duration of air-carriage of respiratory droplets and droplet nuclei Exhaled droplets due to talking and coughing Toward understanding the risk of secondary airborne infection: Emission of respirable pathogens Respiratory protective devices -Methods of test and test equipment -Part 5: Breathing machine, metabolic Simulator, RPD headforms and torso, tools and verification tools -Amendment 1: PRD head forms front and side views Development of a manikin-based performance evaluation method for loose-fitting powered air-purifying respirator No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted