key: cord-260429-5wsj003j
authors: Kenyon, Chris
title: Widespread use of face masks in public may slow the spread of SARS CoV-2: an ecological study
date: 2020-04-06
journal: nan
DOI: 10.1101/2020.03.31.20048652
sha: 
doc_id: 260429
cord_uid: 5wsj003j

Background The reasons for the large differences between countries in the sizes of their SARS CoV2 epidemics is unknown. Individual level studies have found that the use of face masks was protective for the acquisition and transmission of a range of respiratory viruses including SARS CoV1. We hypothesized that population level usage of face masks may be negatively associated SARS CoV2 spread. Methods At a country level, linear regression was used to assess the association between COVID19 diagnoses per inhabitant and the national promotion of face masks in public (coded as a binary variable), controlling for the age of the COVID19 epidemic and testing intensity. Results Eight of the 49 countries with available data advocated wearing face masks in public: China, Czechia, Hong Kong, Japan, Singapore, South Korea, Thailand and Malaysia. In multivariate analysis face mask use was negatively associated with number of COVID19 cases/inhabitant (coef. -326, 95% CI -601- -51, P=0.021). Testing intensity was positively associated with COVID-19 cases (coef. 0.07, 95% CI 0.05-0.08, P<0.001). Conclusion Whilst these results are susceptible to residual confounding, they do provide ecological level support to the individual level studies that found face mask usage to reduce the transmission and acquisition of respiratory viral infections.

SARS CoV-2, the viral cause of COVID-19, has spread rapidly to over 190 countries 63

[1]. There has, however, been remarkable variation in how extensively it has spread 64 and in the national responses to this spread [1, 2] . For example, although the virus is 65 thought to have first emerged in China, European countries such as Italy and Spain 66 have reported roughly 30-fold higher number of infections per capita than China [1, 67 2]. Understanding the reasons underpinning this heterogeneity in spread is crucial to 68 ongoing prevention efforts. The cornerstones of prevention efforts have included 69 extensive testing, contact tracing and isolation and various forms of social 70 distancing/quarantining [3, 4] . Whilst there have been important differences in how 71 these were implemented in different countries, arguably the most striking difference 72 in approach has been in the use of universal face masks in public. Whereas a 73 number of predominantly Asian countries have promoted this practice, the World 74

Health Organization (WHO) and most European and North American countries have 75 not promoted this strategy [5, 6] . The head of the Chinese Center for Disease 76

Control and Prevention has stated that the biggest mistake that Europe and the US 77 were making in tacking COVID-19 was their failure to promote the widespread usage 78 of face masks in public [7] . The WHO argues against universal face mask use 79 based on a lack of evidence to support the practice, as well as a concern that using 80 face masks will provide users with a false sense of security which may result in 81 poorer hand hygiene and hence increased transmission [3, 5, 8] . The US Centers for 82 Disease Control and Prevention does not recommend that people who are well wear 83 a face mask to protect themselves from respiratory diseases, including COVID-19 84

[5]. In fact, the US Surgeon General stated that facemasks "are not effective in 85 . 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 //doi.org/10. /2020 preventing (the) general public from catching coronavirus" and urged people to 86 stop buying face masks [5] . 87

Advocates of universal usage of face masks point to four types of evidence. Firstly, 89 SARS CoV-1 and -2 are spread mainly through contact-and droplet-but also 90 through airborne-transmission [6, 9] . Detailed environmental and epidemiological 91 investigations from the large Amoy Gardens outbreak of SARS CoV-1 revealed that 92 airborne transmission played an important role in the outbreak [10, 11] . Likewise in 93 vitro studies demonstrate that SARS CoV-2 can be aerosolized and remain viable in 94 the air in this form for at least 3 hours [12] . Although viral viability was not assessed, 95 air samples from hospital rooms and toilets used by COVID-19 patients as well as 96 from a crowded entrance to a department store tested positive for SARS . 97

Even if we discount the evidence of airborne transmission, face masks could play a 98 major role in reducing droplet and possibly contact (via reduced digital-oral 99 interactions) transmission. The second type of evidence is that from epidemiological 100 studies showing that masks do provide this protective effect. One systematic review 101 on the efficacy of face masks to prevent influenza, found evidence that face masks 102 were effective in preventing the transmission to others and weaker evidence that 103 they prevented influenza acquisition [14] . Likewise, a systematic review and 104 metanalysis in health care workers found that mask wearing was associated with a 105 lower incidence of clinical respiratory infections [15] . A Cochrane review of different 106 physical measures to prevent the acquisition of respiratory viruses found face masks 107 to be the most effective of all measures investigated -including social distancing 108

[16]. The results were similar for studies limited to SARS CoV-1 transmission, with 109 the authors concluding: 'wearing a surgical mask or a N95 mask is the measure with 110 . 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/10.1101/2020.03.31.20048652 doi: medRxiv preprint the most consistent and comprehensive supportive evidence' [16] . Thirdly, there is 111 increasing evidence that a large proportion of SARS CoV-2 transmission occurs from 112 pauci-or asymptomatic individuals. An estimated 30% of infections are truly 113 asymptomatic and 80% mild infections [17] . Evidence is also mounting that infected 114 individuals are infectious prior to the onset of symptoms [18] . Taken together these 115 findings provide an explanation for why epidemiological studies have found that 116 nondocumented infections were the infection source for 79% of documented cases 117

in Wuhan, China [18] . In this setting limiting masks to confirmed infections is far less 118 likely to have an impact on transmission than universal use. The key argument for 119 universal use is thus preventing transmission and a secondary argument is 120 preventing acquisition [7, 9] . 

Linear regression was used to analyze the association between the independent and 152 dependent variables. We controlled for the fact that SARS CoV-2 epidemic is at 153 different stages in different countries via two methods. Firstly, the 'age of the 154 epidemic' variable was included in all analyses. Secondly, we only included countries 155 with at least 500 cumulative cases and countries whose first case was reported 156 before 7 March 2020. Countries with missing data were dropped from the analyses. 157

The analysis was performed in STATA version 16 (Stata Corp, College Station, Tx). 158

Although Hong Kong is a part of China it was included as a separate data point in 159 . 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 . 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 //doi.org/10. /2020 In this ecological study we found that countries that promoted widespread face mask 185 usage had lower cumulative numbers of COVID-19 diagnosed after controlling for 186 testing intensity and age of the epidemic. It is important to note that this association 187 may be entirely explained by unmeasured confounders. For example, if countries 188 promoting universal face masking also conducted more effective contact tracing and 189 isolation than other countries and this was responsible for the slower spread, our 190 study design would have falsely attributed this effect to using face masks. We did not 191 have accurate data to control for these confounders. We did however control for 192 testing intensity which is an important potential confounder. We also controlled for 193 the age of the epidemic which is an obvious independent determinant of the size of 194 the epidemic. A further limitation of our study was that we were unable to quantitate 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 //doi.org/10. /2020 There are a number of countries in Western European such as Italy that have 209 conducted intensive screening, contact tracing, isolation, social distancing and 210 widespread lockdowns and yet have amongst the largest COVID-19 epidemics in the 211 world [2] . A striking omission from this response-list if we compare it to the 212 responses in China and other Asian countries with lower COVID-19 incidence is that 213 the widespread use of face masks in public was not promoted. The only European 214 country to adopt this strategy was Czechia, and it did so at a relatively late stage in 215 the epidemic [19, 20] . Early indications suggest that despite higher testing rates than 216 the average for western European countries, the number of new infections is lower in 217

Czechia [1] . Future studies will however be crucial to evaluate the impact of this 218 intervention in Czechia and elsewhere. These studies may benefit from including 219 data from Taiwan and Macau where use of face masks in public has been high and 220 the cumulative number of infections has remained so low that they did not meet the 221 It is likely that a single intervention is not sufficient to suppress the spread of COVID-225 19 [2]. The safest approach in the middle of this epidemic may be to introduce the 226 full package of interventions that have been proven to work in Asian countries and 227 then scale back according to new findings [3, 9] . Our analysis provides further 228 evidence that this package should include widespread usage of face masks in public. 229

Currently the only European country that can be considered to be doing this is 230

Czechia. 231 232 . 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 Authors' contributions 233 CK conceptualized the study, was responsible for the acquisition, analysis and 234 interpretation of data and wrote the analysis up as a manuscript. 235 236

Nil 238 239

The author declares that he/she has no competing interests. 241 242

The analysis involved a secondary analysis of public access ecological level data. As 244 a result, no ethics approval was necessary. 245 246

Not applicable 248

Nil 250 251 . 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 . 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 

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