key: cord-0894283-z86g8dzs authors: Esposito, Susanna; Principi, Nicola; Leung, Chi Chi; Migliori, Giovanni Battista title: Universal use of face masks for success against COVID-19: evidence and implications for prevention policies date: 2020-04-29 journal: Eur Respir J DOI: 10.1183/13993003.01260-2020 sha: 74c0e0cea7d112fb4514672dbbb8aafa6316bbed doc_id: 894283 cord_uid: z86g8dzs Cloth masks are a simple, economic and sustainable alternative to surgical mask as a means of source control of SARS-CoV-2 for general community. A hot debate is taking place on the use of face masks (including cloth and surgical) as a prevention tool in the community vis-à-vis the recent World Health Organization (WHO) recommendations. To shed light on this important topic we reviewed relevant literature focused on the key words "infection control", "prevention", "masks", "respirators", "viral infections" and "COVID-19" without time restrictions to identify a minimum set of references from an electronic database (PUBMED), existing guidelines, viral diseases, airborne diseases, and grey literature. The core findings of the references identified are summarised in Table 1 . According to the WHO report from February 2020 (https://www.who.int/docs/defaultsource/coronaviruse/who-chinajoint-mission-on-covid-19-final-report.pdf.), the proportion of truly asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was relatively small and not a major driver of virus circulation, infection transmission, and new disease development. However, in blanket testing of an isolated village of approximately 3,000 people in northern Italy, 50%-75% of people with positive pharyngeal molecular tests were totally asymptomatic [1] . This finding was echoed by a more recent daily surveillance report from China, where all people arriving from overseas were rigorously tested [2] : among 166 persons with newly identified infections, 78% were asymptomatic. Although the infective dose associated with transmission is not known, the viral load in the respiratory tract in an asymptomatic patient has been reported to be similar to patients with symptoms [3] , and transmission of SARS-CoV-2 infection from an asymptomatic contact has also been described [4] . Until some weeks ago, it was thought that the virus could be transmitted only by droplets that are coughed or sneezed out or by contaminated fomites, with differences according to the initial load and surface characteristics [5] . Airborne transmission of SARS-CoV-2 was considered possible only when care procedures generating aerosols (e.g. intubation, bronchoscopy, and positive-pressure ventilation) are performed [6] . However, other studies seem to indicate the opposite, i.e., the virus can be present in exhaled air produced by talking and breathing [6] . Moreover, a potential role of aerosols in virus diffusion was evident in a complex laboratory study. Aerosols containing a viral load quite similar to that observed in human respiratory samples were created to generate an aerosolized environment. SARS-CoV-2 was detected up to 3 hours after the start of the study [7] . Although these findings were not considered fully convincing by some authors [5] , they deserve attention and require further studies to establish whether and when airborne transmission of SARS-CoV-2 truly occurs and how it can be reduced. It is well known that surgical masks can prevent the inhalation of large droplets and sprays but have limited ability to filter submicron-sized airborne particles [8, 9] . As SARS-CoV-2 is also embedded in aerosols <5 μm in diameter, it cannot be determined whether they are always effective. However, mask wearing by patients with pulmonary tuberculosis (an airborne infectious disease) has been shown to reduce infectivity to guinea pigs by 56% [9, 10] . The surgical mask has also been shown to intercept other human coronaviruses during coughing [11] . A meta-analysis of randomized controlled trials also showed that surgical masks and N95 respirators were similarly effective in preventing influenza-like illness and laboratory-confirmed influenza among healthcare workers [12] . Similar results were obtained in a case-control study comparing the protective effect of surgical masks and N95 respirators against SARS among healthcare workers in five Hong Kong hospitals [13] . Controlling a respiratory infection at source by a face mask is a well-established strategy. For example, symptomatic patients with cough or sneezing are generally advised to put on a face mask, and this applies equally to patients with pulmonary tuberculosis (airborne transmission) and influenza (predominantly droplet-transmitted). With the large number of asymptomatic patients unware of their own infection [1, 2] , the comparable viral load in their upper respiratory tract [3] , droplet and aerosol dispersion even during talking and breathing [6] , and prolonged viral viability outside our body [7] , we strongly advocate universal use of face mask as a means of source control in public places during the COVID-19 pandemic. Extreme forms of social distancing is not sustainable, and complete lockdown of cities or even whole countries is extremely devastating to the economy. Universal masking in public complements social distancing and hand hygiene in containing or slowing down the otherwise exponential growth of the pandemic. Universal masking protects against crosstransmission through unavoidable person-to-person contact during the lockdown and reduces the risk for resurgence during relaxation of social distancing measures on reopening. A high degree of compliance will maximize the impact of universal masking in public. The global shortage of surgical masks and N95 respirators is a serious concern. In line with the recent recommedation by US CDC for healthy people to wear a cloth face cover in public [14] , we strongly support the use of cloth masks as a simple, economic and sustainable alternative to surgical mask as a means of source control for general community use, so that disposable surgical masks and N95 respirators can be reserved for use in health care facilities. Such intervention is likely to be life-saving in many resource limited settings. S.E. and N.P. co-wrote the manuscript. GBM and CCL wrote sections of the manuscript, edited the text for major intellectual components and designed the Table. All authors approved the text. Authors declare no competing interests. Covid-19: identifying and isolating asymptomatic people helped eliminate virus in Italian village Covid-19: four fifths of cases are asymptomatic, China figures indicate SARS-CoV-2 viral load in upper respiratory specimens of infected patients Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations Is the coronavirus airborne? Experts can"t agree Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 Wearing surgical masks in public could help slow COVID-19 pandemic's advance: Masks may limit the spread diseases including influenza, rhinoviruses and coronaviruses Reducing tuberculosis transmission: a consensus document from the World Health Organization Regional Office for Europe Surgical face masks worn by patients with multidrug-resistant tuberculosis: impact on infectivity of air on a hospital ward Respiratory virus shedding in exhaled breath and efficacy of face masks Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysis Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS) How to Protect Yourself & Others The article is part of the activities of WAidid (World Association for Infectious Diseases and Immunological Disorders), the Global Tuberculosis Network (GTN) and the WHO Collaborating Centre for Tuberculosis and Lung Diseases, Tradate, ITA-80, 2017-2020-GBM/RC/LDA.). Core recommendations are: 1. Clean your hands often; 2. Avoid close contact; 3. Cover your mouth and nose with a cloth cover when around others; 4. Cover cough and sneezes; 5. Clean and disinfect.