Masks for Prevention of COVID-19 in Community and Healthcare Settings

Roger Chou; Tracy Dana; Rebecca Jungbauer; Chandler Weeks; Marian S. McDonagh

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Masks for Prevention of COVID-19 in Community and Healthcare Settings

Rapid Evidence Product

Roger Chou, M.D., FACP, Tracy Dana, M.L.S., Rebecca Jungbauer, Dr.P.H., Chandler Weeks, M.P.H., and Marian S. McDonagh, Pharm.D.

Rockville (MD): Agency for Healthcare Research and Quality (US); 2020 Jun 24.

Report No.: 20-EHC019

Background and Purpose

Currently, no proven treatments are available for coronavirus disease 2019 (COVID-19), the disease caused by infection with the novel (new) coronavirus SARS-CoV-2. Therefore, clinicians and policymakers advise preventive measures. This rapid review addresses the comparative effectiveness of various types of facemasks in the community and in healthcare workers (HCWs) for prevention of infection with SARS-CoV-2 and the effectiveness and safety of mask re-use. Given this rapidly emerging field and the urgent need for answers, the AHRQ Evidence-based Practice Center (EPC) program is updating this report on a regular basis. The original review was based on searches through May 6, 2020, and this update is based on searches through June 2, 2020. Comments and any unpublished data should be sent to vog.shh.qrha@cpe, and appropriate changes will be made in the subsequent version.

Several types of respirators and facemasks (collectively referred to in this report as facemasks) are available for potentially preventing infection with SARS-CoV-2. Disposable N95 filtering facepiece (and equivalent) respirators are devices designed to achieve a very close facial fit and very efficient filtration of airborne particles (blocking at least 95% of very small [0.3 micron] particles). Surgical/medical masks (referred to in this report as surgical masks) are loose-fitting, disposable devices designed to create a physical barrier between the mouth and nose of the wearer and the immediate environment, blocking larger particles and splashes or spatters. Cloth masks are non-medical, unstandardized face coverings that vary in the cloth material used, the number of layers, and tightness of fit. They are generally meant to be washable and reusable. Other respiratory protective devices, such as reusable N95 elastomeric respirators and powered air-purifying respirators are not addressed in this report (the term N95 respirator in this report refers to disposable N95 filtering facepiece respirators).

Recommendations from the World Health Organization and the Centers for Disease Control and Prevention (CDC) on use of facemasks by HCWs have differed with regard to when an N95 respirator or equivalent should be used. The CDC has encouraged the use of cloth masks in the community to prevent asymptomatic spread of COVID-19.¹ Although single-use N95 and similar respirators are considered to provide superior respiratory protection for HCWs compared with surgical masks,² shortages have been reported in the United States and elsewhere.³ Reuse of N95 and equivalent respirators has been tested in laboratory settings,⁴ but clinical effectiveness and safety of mask re-use in practice is unknown.⁴^,⁵

Key Questions

The Key Questions used to guide this rapid review were developed with input from staff at the American College of Physicians and the Agency for Healthcare Research and Quality.

What is the effectiveness of respirators (e.g., N95) versus facemasks (surgical) versus cloth masks for prevention of COVID-19 in addition to standard precautions (gowns + gloves + handwashing)?
1. In community settings
2. In healthcare settings
  1. In high-risk healthcare settings (e.g., intensive care unit, emergency room)
  2. In healthcare settings with close contact but unknown risk (e.g., primary care, other settings)
What is the evidence for extended or reuse of N95 respirators for prevention of COVID‑19?

Evidence Summary

Methods

Detailed methods are available in Appendix A.

A medical librarian searched PubMed MEDLINE^® and Elsevier Embase^® (from 2003 through April 14, 2020) (Appendix A). The original report was based on surveillance for new studies through May 6, 2020; this update includes surveillance through June 2, 2020. The World Health Organization Global Literature on Coronavirus Disease database⁶ and the medRxiv preprint server⁷ were also searched. Reference lists of systematic reviews and included studies were reviewed for additional studies.

Because evidence on facemasks and SARS-CoV-2 infection is currently limited, this report also includes evidence about the use of facemasks and effects on risk of other respiratory infections, including other coronaviruses involved in epidemic respiratory illness outbreaks (SARS-CoV-1, the cause of severe acute respiratory syndrome-1 [SARS-1] and MERS-CoV, the cause of Middle East Respiratory Syndrome [MERS]), influenza and influenzalike illness, and other viral respiratory illness. This report does not include laboratory or animal studies or modeling studies, which may also inform decisions regarding mask use in the absence of more direct evidence.

Evidence Base

Searches identified 1,742 citations, of which 39 studies were relevant.⁸^–⁴⁶ One observational study (identified from reference lists) of N95 and surgical masks in healthcare settings was added for this update.⁴⁶ For Key Question (KQ) 1, there were 18 randomized controlled trials (RCTs) (Appendix Table B-1) and 21 observational studies (Appendix tables B-2 and B-3). Twelve RCTs⁸^–¹⁰^,¹²^,¹³^,¹⁷^,¹⁸^,²⁰^,²⁷^,³¹^,³⁸^,³⁹ and three observational studies²¹^,⁴¹^,⁴⁴ were conducted in the community or non-HCWs, and six RCTs¹⁶^,²⁴^,²⁸^–³⁰^,³⁶ and 18 observational studies¹¹^,¹⁴^,¹⁵^,¹⁹^,²²^,²³^,²⁵^,²⁶^,³²^–³⁵^,³⁷^,⁴⁰^,⁴²^,⁴³^,⁴⁵^,⁴⁶ were conducted in HCWs. None of the RCTs addressed effects of masks on risk of infection with SARS-CoV-2, SARS-CoV-1, or MERS-CoV. Rather, the RCTs were usually conducted during influenza season and evaluated the risk of nonspecific clinical respiratory illness, influenzalike illness, and laboratory-confirmed viral respiratory illness. Of the observational studies, two cohort studies addressed SARS-CoV-2,¹⁹^,⁴² 18 studies addressed SARS-CoV-1 (6 cohort studies¹⁴^,²⁵^,³³^,³⁵^,⁴³^,⁴⁶ and 12 case-control studies¹⁵^,²¹^–²³^,²⁶^,³²^,³⁴^,³⁷^,⁴⁰^,⁴¹^,⁴⁴^,⁴⁵), and one cohort study addressed MERS-CoV.¹¹ Two Chinese-language studies were translated into English by a native Chinese speaker at the EPC.²⁶^,⁴⁵ Figure 1 summarizes the study selection process. A list of included studies is provided in Appendix C.

Two RCTs¹⁶^,²⁴ were randomized by individual participant; the remaining trials were randomized by clusters (households, university residence halls, tents during Hajj, hospitals, hospital wards, or outpatient settings). The numbers of participants ranged from 164 to 7,687. The RCTs were conducted during influenza season, with the exception of two RCTs conducted among pilgrims staying in tents during Hajj.¹⁰^,¹² Two RCTs²⁴^,²⁷ reported the incidence of laboratory-confirmed nonpandemic coronavirus infections, but there was only one case in one trial.²⁷ Four trials were conducted in the United States, one in Canada, one in Australia, two in Europe, two in Saudi Arabia, and eight in Asia. Eleven RCTs were rated good quality and seven were rated fair quality (Appendix D). Limitations in the fair-quality trials included baseline differences between groups and high attrition; one cluster RCT¹² did not adjust for cluster correlation. Blinding of participants to the mask and other interventions (e.g., hand hygiene) was not possible.

The observational studies had important limitations (Appendix tables B-2 and B-3). All were retrospective and potentially susceptible to recall bias for determining mask use and other exposures. The studies were generally limited in their ability to measure and control for the amount and intensity of exposures. Six studies did not attempt to control for potential confounders. Of the 15 studies that did control for confounders, only one²³ evaluated correlations between masks and other infection control measures (e.g., gloves, gowns, goggles, or handwashing) to inform selection of variables for model building. In the other studies that reported results from multivariate models, correlations between infection control measures and potential collinearity were not addressed.

KQ 1. What is the effectiveness of respirators (e.g. N95) versus facemasks (surgical) versus cloth masks for prevention of COVID-19 in addition to standard precautions (gowns + gloves + handwashing)?

Community Settings

Twelve RCTs evaluated masks in community settings (Appendix Table B-1).⁸^–¹⁰^,¹²^,¹³^,¹⁷^,¹⁸^,²⁰^,²⁷^,³¹^,³⁸^,³⁹ The settings were households, university residence halls, and tents used by pilgrims during Hajj. Masks were used by index cases, household contacts of index cases, cases and contacts, or people without specific contact with cases. Participants in the trials generally received education on preventing respiratory infection and hand hygiene regardless of whether they were randomized to masks or another intervention. All of the trials compared a mask versus no mask. One trial also compared a mask versus a mask plus hand washing training.³⁸ In addition, three trials compared a mask versus hand hygiene¹⁷^,¹⁸^,²⁰ and two trials compared a mask plus hand sanitizer versus hand sanitizer alone;⁸^,⁹^,³⁹ these comparisons were beyond the scope of this report and are not discussed further, though data are shown in Appendix Table B-1.

Only one RCT directly compared different mask types.²⁷ It evaluated a P2 mask (Australian equivalent to an N95) versus a surgical mask in adult household contacts of children with influenzalike illness. There were no differences between either mask type versus a no-mask control in infection outcomes, though estimates were imprecise. The RCT did not report a cluster adjusted risk estimate for the P2 versus the surgical mask, but the calculated (crude) unadjusted estimate was not statistically significant. Adherence to masks was poor in the trial, which could have reduced effectiveness. In a multivariate analysis, adherence to either mask was associated with decreased risk of influenzalike illness (hazard ratio 0.26 to 0.32).

Seven other trials, in addition to the trial described above, evaluated use of surgical masks within households with an influenza or influenzalike illness index case (child or adult).¹³^,¹⁷^,¹⁸^,²⁰^,³¹^,³⁸^,³⁹ Compared with no masks, surgical masks were not associated with decreased risk of clinical respiratory illness, influenzalike illness, or laboratory-confirmed viral illness in household contacts when masks were worn by household contacts,²⁰^,²⁷^,³⁸ index cases,¹³^,³¹ or both.¹⁷^,¹⁸^,³⁹ However, some estimates were imprecise, adherence to mask-wearing was limited, and some crossover occurred. Two trials found no differences between surgical masks plus handwashing versus handwashing alone in risk of infections in household contacts of index cases.²⁰^,³⁸

Two trials of students living in university residence halls without specific contacts with cases also found no significant differences between a surgical mask versus no mask and risk of influenzalike illness.⁸^,⁹ Surgical masks, compared with no masks, were not associated with decreased risk of infections in Hajj pilgrims with or without an infected index case within the same tent.¹⁰^,¹²

Three observational studies evaluated effects of masks on risk of SARS-1 in community settings or non-HCWs (Appendix Table B-2).²¹^,⁴¹^,⁴⁴ None of the studies compared one mask type with another. In addition, the studies did not provide details regarding mask type. Wearing a mask was associated with decreased risk of infection in persons without known contacts with SARS-1 patients in one study⁴⁴ and in household contacts of persons with SARS-1 in two studies.²¹^,⁴¹

Healthcare Settings

Six RCTs evaluated masks in HCWs in healthcare settings (Appendix Table B-1).¹⁶^,²⁴^,²⁸^–³⁰^,³⁶ One was a pilot trial that reported adherence and harms but not effects on risk of HCW infections.¹⁶ Of the other five trials, four compared an N95 versus surgical mask and one²⁸ compared a surgical versus cloth mask. In the trials, masks were generally used in addition to other personal protective equipment (PPE) items and handwashing, though details regarding other infection control measures were limited.

Three RCTs compared N95 respirators versus surgical mask in higher-risk settings (e.g., emergency department, respiratory wards, pediatric wards, intensive care units).²⁴^,²⁹^,³⁰ One trial found an N95 and surgical mask were both associated with very similar likelihood of a physician visit for acute respiratory illness (6.2% vs. 6.1%).²⁴ Two trials found an N95 associated with decreased risk of clinical respiratory illness, with absolute differences that ranged from −2.8% to −7.7%.²⁹^,³⁰

In all three trials, there were few cases of influenzalike illness, resulting in imprecise estimates. For laboratory-confirmed viral respiratory infections, one trial²⁴ that did not require HCWs to have symptoms found no difference between an N95 versus surgical mask in risk of infections. In the other two trials, laboratory-confirmed viral respiratory illness was only diagnosed in symptomatic patients; the number of cases was small and estimates were imprecise. One trial reported no difference in the subgroup of laboratory-confirmed (not necessarily symptomatic) viral infections by nonpandemic coronaviruses, based on a total of 21 cases.²⁴ The other two trials did not report nonpandemic coronavirus infections.

Two of the trials described above included two N95 respirator arms. One of the trials found that effects of an N95 versus surgical mask on clinical respiratory illness were similar for fit-tested and non-fit-tested N95s (4.6% vs. 3.3%).²⁹ The other trial found that continuous N95 use (at all times while working) was associated with a small decrease in risk of clinical respiratory illness versus intermittent (only during high-risk procedures or barrier situations) N95 use (7.2% vs. 11.8%).³⁰

One other trial of HCWs in higher-risk settings found a surgical mask associated with decreased risk of clinical respiratory illness, influenzalike illness, and laboratory-confirmed viral infections when compared with cloth masks, but estimates were imprecise and not statistically significant.²⁸

One trial of HCWs in lower-risk outpatient settings found no differences between an N95 versus surgical mask in risk of clinical respiratory illness, influenzalike illness, laboratory-confirmed viral illness, or laboratory-confirmed influenza.³⁶

Eighteen observational studies (including one additional study identified for this update⁴⁶) evaluated the association between mask use by HCWs or directness of contact and risk of infection with SARS-CoV-2, SARS-CoV-1, or MERS-CoV.¹¹^,¹⁴^,¹⁵^,¹⁹^,²²^,²³^,²⁵^,²⁶^,³²^–³⁵^,³⁷^,⁴⁰^,⁴²^,⁴³^,⁴⁵^,⁴⁶ Two studies evaluated effects of masks on risk of infection with SARS-CoV-2, 15 studies on risk of infection with SARS-CoV-1, and one study on risk of infections with MERS-CoV (Appendix Table B-3).

Two cohort studies evaluated the association between mask use and risk of SARS-CoV-2 infections but had important limitations. One study found N95 respirators associated with decreased risk of infection versus no mask,⁴² but mask use was based on whether the HCW worked in a department in which masks were used, not on assessment of individual use.⁴² In addition, confounding was likely because departments in which N95s were used also differed from the non-N95 departments in use of handwashing, other infection control measures, and exposure to COVID-19 patients. There were also few HCW cases and serious imprecision. The other study was small (n=37) and only reported three cases of SARS-CoV-2 infection in HCWs, resulting in very imprecise estimates regarding the association with mask use.¹⁹

Five observational studies consistently found an N95 respirator associated with decreased risk of SARS-CoV-1 infection versus a surgical mask (sometimes described as a “disposable” mask) in HCWs.¹⁴^,²³^,²⁵^,³⁵^,⁴⁶ Results of three comparisons involving an N95 or surgical versus cloth mask and risk of SARS-CoV-1 infection were somewhat inconsistent.²³^,²⁶^,⁴⁵ In addition, the applicability of the cloth masks evaluated in these studies to other settings may be limited, as they were described as 12- or 16-layer masks, or many more layers than typically found in cloth masks in the United States and other countries where cloth masks typically have far fewer layers.

Twelve observational studies consistently found mask use associated with decreased risk of SARS-CoV-1 infection versus no use;²³^,²⁵^,²⁶^,³²^–³⁵^,³⁷^,⁴⁰^,⁴³^,⁴⁵^,⁴⁶ of these, eight specifically evaluated N95 or surgical masks.²³^,²⁵^,²⁶^,³⁵^,³⁷^,⁴⁰^,⁴⁵^,⁴⁶ Masks were usually associated with decreased risk of SARS-CoV-1 infection in multivariate models, but in some cases masks were not included as variables in the models. However, correlations between mask use and other infection control measures could have impacted variable selection for model building, but were not described.

Four studies found more consistent use of masks associated with decreased risk of SARS-CoV-1 or MERS-CoV infection versus less consistent use;¹¹^,²²^,²⁵^,³³ of these, three specifically evaluated N95 or surgical masks. In one of the studies, consistent use of N95 or surgical masks was associated with decreased risk of infections in HCWs with direct contact with SARS-1 patients or direct patient contact in general, as well as in HCWs without direct patient contact.²²

Harms

Reporting of harms in the RCTs was suboptimal, but did not indicate serious harms associated with use of masks (Appendix Table B-1). When reported, the most common adverse events were discomfort, breathing difficulties, and skin events. One trial found an N95 respirator associated with increased risk of headache and breathing difficulty compared with a surgical mask in HCWs,²⁹ but one trial found no difference between a P2 (N95 equivalent) respirator versus surgical mask in adverse events in persons in the community.²⁷ One trial reported no differences in harms between a surgical versus cloth mask in HCWs.²⁸

Key Question 2. What is the evidence for extended or reuse of N95 respirators for prevention of COVID-19?

No study evaluated effects of extended or reuse of N95 respirators and risk of COVID-19.

Conclusions and Future Research

The main findings of this update are unchanged from the original review. The updated results include one additional observational study⁴⁶ (identified from reference lists) conducted in a healthcare setting that reported imprecise estimates for N95 and surgical masks. Direct evidence on the effectiveness and comparative effectiveness of masks for preventing COVID-19 due to SARS-CoV-2 infection is lacking. Therefore, it was necessary to also consider evidence on masks and risk of other respiratory infections. However, the applicability of such evidence to COVID-19 is uncertain. This report does not include laboratory or animal studies or modeling studies, which could also inform decisions regarding mask use in the absence of more direct evidence.

In community settings, one RCT found no difference between N95 or equivalent respirators versus surgical masks for prevention of noncoronavirus respiratory illness. Evidence from RCTs in community settings typically conducted within households or enclosed spaces during influenza seasons did not indicate effectiveness of masks in general for reducing risk of viral respiratory infections but also found suboptimal mask compliance. Observational data on effectiveness of masks for preventing infections associated with epidemic coronaviruses were limited, but suggest masks in general might be associated with reduced risk of SARS-1. This could be related to higher mask compliance in the setting of pandemic outbreaks, greater effectiveness of masks for SARS-1, or residual confounding. Applicability of findings and mask compliance from studies conducted in households or other enclosed spaces in which there was often prolonged close contact with an index case to mask wearing in public without known or prolonged exposure may be limited.

In HCWs, RCTs indicate that N95 and surgical masks are probably associated with similar risk of influenzalike illness and laboratory-confirmed viral infections in high- and low-risk settings. However, there was some inconsistency in effects of N95 versus surgical masks on clinical respiratory infections in high-risk settings, with one good quality trial showing no difference in physician visits for respiratory illness and two fair quality, cluster-randomized trials showing N95 masks associated with a small decrease in risk. The only trial comparing N95 versus surgical masks in a low-risk (primary care) setting found no difference in risk of clinical respiratory illness. Observational studies suggest that N95 masks might be associated with decreased risk of SARS-CoV-1 infections compared with surgical masks, and mask use in general is probably associated with decreased risk of SARS-CoV-1 infection. There was no evidence to address effects of extended or re-use of N95 respirators on risk of infection, though evidence on effects of extended or reuse for nonclinical outcomes (e.g., measures of filtration, contamination, and mask failure) has been summarized elsewhere.⁴ Table 1 summarizes the strength of evidence for key comparisons and outcomes.

Research is urgently needed to understand the effectiveness and comparative effectiveness of masks for preventing COVID-19 in community and healthcare settings and to understand the effects of extended and re-use of N95 respirators. Ongoing studies (Appendix E) include an RCT comparing disposable N95 respirators versus surgical masks in HCWs (estimated completion December 2020),⁴⁷ a longitudinal study on risk factors for COVID-19 in HCWs (estimated completion September 2020),⁴⁸ and a randomized trial on surgical masks versus no mask in the community and risk of COVID-19 (estimated completion July 2020).⁴⁹ The World Health Organization has also published a protocol for a prospective study on risk factors for COVID-19 in HCWs.⁵⁰

This figure is a literature flow diagram depicting the search and selection of articles. The diagram shows that 1,732 records were identified through database searching and 10 additional records were identified through other sources such as reference lists and hand searching. In total, 1,742 records were screened at the abstract level for inclusion, and 1,609 of these abstracts were excluded leaving 133 articles to be assessed at the full-text level. Of these 133 full-text articles, 94 were excluded. The remaining 39 articles were included for Key Question 1 and zero were included for Key Question 2. For Key Question 1, 2 studies on SARS-CoV-2 were conducted in a healthcare setting and none were conducted in a community setting; 16 studies on SARS-CoV-1/MERS-CoV were conducted in a healthcare setting and 3 in a community setting; and 6 studies on influenza, influenza-like illness, or other viral respiratory illness were conducted in a healthcare setting and 12 in a community setting.

Figure 1

Literature flow diagram. Abbreviations: ILI = influenzalike illness; MERS-CoV = virus causing Middle East Respiratory Syndrome; SARS-CoV-1 = virus causing Severe Acute Respiratory Syndrome-1; SARS-CoV-2 = virus causing Coronavirus 2019; VRI = viral respiratory (more...)

Table 1

Summary of evidence.

Glossary

COVID-19:: Coronavirus Disease 2019; the disease caused by the novel coronavirus SARS-CoV-2. In this report, the term COVID-19 is used when referring to patients with SARS-CoV-2 infection meeting the COVID-19 case definition.
MERS-CoV:: The virus causing MERS. In this report, “MERS-CoV infection” is used when referring to infection with MERS-CoV that does not necessarily meet the case definition for MERS (e.g., laboratory diagnosis of SARS-CoV-1 infection but asymptomatic, mildly symptomatic, or symptom status not reported).
MERS:: Middle East Respiratory Syndrome; the disease caused by the coronavirus MERS-CoV. In this report, the term MERS-CoV is used when referring to patients with MERS-CoV infection meeting the MERS case definition.
SARS-CoV-1:: The virus causing SARS-1. In this report, “SARS-CoV-1 infection” is used when referring to infection with SARS-CoV-1 that does not necessarily meet the case definition for SARS-1 (e.g., laboratory diagnosis of SARS-CoV-1 infection but asymptomatic, mildly symptomatic, or symptom status not reported).
SARS-CoV-2:: The virus causing COVID-19. In this report, “SARS-CoV-2 infection” is used when referring to infection with SARS-CoV-2 that does not necessarily meet the case definition for COVID-19 (e.g., laboratory diagnosis of SARS-CoV-12infection but asymptomatic, mildly symptomatic, or symptom status not reported).
SARS-1:: Severe Acute Respiratory Syndrome-1; the disease caused by the coronavirus SARS-CoV-1. In this report, the term SARS-1 is used when referring to patients with SARS-CoV-1 infection meeting the SARS-1 case definition.

Afterword

Recognized for excellence in conducting comprehensive systematic reviews, the Agency for Healthcare Research and Quality (AHRQ) Evidence-based Practice Center (EPC) program is developing a range of rapid evidence products to assist end-users in making specific decisions in a limited timeframe.

The AHRQ EPC Program recognizes that people are struggling with urgent questions on how to control the COVID-19 pandemic. To shorten timelines, reviewers make strategic choices about which review processes to abridge. However, the adaptations made for expediency may limit the certainty and generalizability of the findings from the review, particularly in areas with a large literature base. Transparent reporting of the methods used and the resulting limitations of the evidence synthesis are extremely important.

Given the rapidly evolving field, the AHRQ EPC Program will update these reviews on a regular basis to keep the medical community and public up to date as more studies are published through the summer of 2020. If you have comments or have unpublished data to share related to this report, they may be sent by mail to the Task Order Officer named below at: Agency for Healthcare Research and Quality, 5600 Fishers Lane, Rockville, MD 20857, or by email to vog.shh.qrha@cpe and will be considered in the next version of the report.

Gopal Khanna, M.B.A
Director
Agency for Healthcare Research and Quality
Stephanie Chang, M.D., M.P.H.
Director
Evidence-based Practice Center Program
Center for Evidence and Practice Improvement
Agency for Healthcare Research and Quality
Christine S. Chang, M.D., M.P.H
Associate Director
Evidence-based Practice Center Program
Center for Evidence and Practice Improvement
Agency for Healthcare Research and Quality
Arlene S. Bierman, M.D., M.S.
Director
Center for Evidence and Practice Improvement
Agency for Healthcare Research and Quality
Jill S. Huppert, M.D., M.P.H.
Task Order Officer
Evidence-based Practice Center Program
Center for Evidence and Practice Improvement
Agency for Healthcare Research and Quality

Appendix A. Methods

Searches

We searched for systematic reviews and primary studies that address the research questions. Systematic reviews were used to identify relevant primary studies.

Search Strategies

Key Question 1

Randomized Controlled Trials

PubMed MEDLINE

(((“Respiratory Protective Devices”[Mesh]) OR (“Masks”[Mesh])) OR ((((“N95”[Title/Abstract] OR “N 95”[Title/Abstract] OR mask[Title/Abstract] OR masks[Title/Abstract]) OR (“N95”[Other Term] OR “N 95”[Other Term] OR mask[Other Term] OR masks[Other Term])) OR (facemask OR facemasks OR FFP)) OR (((airborne OR droplet* OR respirator OR respirators) AND (protect OR protection OR protective OR precaution)) NOT (mechanical[Title/Abstract])))) AND (prevent OR prevents OR prevention OR transmit OR transmission OR infect OR infection OR infected) Filters: Randomized Controlled Trial

Elsevier Embase

Observational Studies

((((“Respiratory Protective Devices”[Mesh]) OR (“Masks”[Mesh])) OR ((((“N95”[Title/Abstract] OR “N 95”[Title/Abstract] OR mask[Title/Abstract] OR masks[Title/Abstract]) OR (“N95”[Other Term] OR “N 95”[Other Term] OR mask[Other Term] OR masks[Other Term])) OR (facemask OR facemasks OR FFP)) OR (((airborne OR droplet* OR respirator OR respirators) AND (protect OR protection OR protective OR precaution)) NOT (mechanical[Title/Abstract])))) AND (prevent OR prevents OR prevention OR transmit OR transmission OR infect OR infection OR infected)) AND (((((“COVID-19” [Supplementary Concept]) OR (“SARS Virus”[Mesh])) OR (“Severe Acute Respiratory Syndrome”[Mesh])) OR (“Middle East Respiratory Syndrome Coronavirus”[Mesh])) OR ((coronavirus[Title/Abstract] OR COVID[Title/Abstract] OR “severe acute respiratory syndrome*”[Title/Abstract] OR SARS[Title/Abstract] OR “middle eastern respiratory syndrome”[Title/Abstract] OR MERS[Title/Abstract]) OR (coronavirus[Other Term] OR COVID[Other Term] OR “severe acute respiratory syndrome*”[Other Term] OR SARS[Other Term] OR “middle eastern respiratory syndrome”[Other Term] OR MERS[Other Term])))

Elsevier Embase

(‘respiratory protection’/exp OR ‘air-purifying respirator’/exp OR ‘face mask’/exp OR n95:ti,ab,kw OR mask:ti,ab,kw OR masks:ti,ab,kw OR facemask:ti,ab,kw OR facemasks:ti,ab,kw OR ffp:ti,ab,kw) AND (prevent OR prevents OR prevention OR transmit OR transmission OR infect OR infection OR infected) AND (‘severe acute respiratory syndrome’ OR ‘sars-related coronavirus’ OR ‘middle east respiratory syndrome’ OR ‘sars’ OR ‘mers’ OR ‘covid’) AND (‘case control study’/de OR ‘cohort analysis’/de OR ‘comparative study’/de OR ‘controlled study’/de OR ‘cross sectional study’/de OR ‘crossover procedure’/de OR ‘observational study’/de OR ‘prospective study’/de OR ‘retrospective study’/de) AND [embase]/lim NOT ([embase]/lim AND [medline]/lim)

Key Question 2

PubMed MEDLINE

(((“Respiratory Protective Devices”[Mesh]) OR (“Masks”[Mesh])) OR ((((“N95”[Title/Abstract] OR “N 95”[Title/Abstract] OR mask[Title/Abstract] OR masks[Title/Abstract]) OR (“N95”[Other Term] OR “N 95”[Other Term] OR mask[Other Term] OR masks[Other Term])) OR (facemask OR facemasks OR FFP)) OR (((airborne OR droplet* OR respirator OR respirators) AND (protect OR protection OR protective OR precaution)) NOT (mechanical[Title/Abstract])))) AND (reuse OR “re use” OR “extended use” OR “multiuse” OR “multi use” OR “multiple use”)

Elsevier Embase

Types of Studies Included

Randomized controlled trials of one mask type versus another for prevention of COVID-19 (the disease caused by SARS-CoV-2 infection), SARS-1 (the disease caused by SARS-CoV-1 infection), and MERS (the disease caused by MERS-CoV infection). influenzalike illness, and laboratory-confirmed viral respiratory illness.
Randomized controlled trials of masks versus no masks (to inform indirect comparisons) for prevention of COVID-19, SARS-1, MERS, influenzalike illness, and laboratory-confirmed viral respiratory illness.
Cohort and case-control studies on effects of mask use and risk for prevention of COVID-19 (the disease caused by SARS-CoV-2 infection), SARS-1 (the disease caused by SARS-CoV-1 infection), and MERS (the disease caused by MERS-CoV infection).
Randomized controlled trials, cohort studies, and case-control studies on re-use or extended use of masks versus standard use for prevention of COVID-19, SARS-1, or MERS.

PICOTS

Participants/Population

Include: Healthcare workers or community members at risk of contracting COVID-19 or other viral respiratory illnesses due to workplace or community-based exposure
Exclude: Bacterial or other non-viral infection; non-respiratory infection

Intervention/Exposure

Include: N95 respirators or equivalent, surgical/medical masks, and cloth masks.
Exclude: Powered air-purifying respirators (PAPR), reusable N95 elastomeric respirators, other types of personal protective equipment (PPE).

Comparator/Control

Include: One type of mask versus another type of mask; mask use versus nonuse; mask single use versus re-use
Exclude: Other personal protective equipment

Context

Include: Community or healthcare settings; mask use by healthcare workers (HCWs) or non-HCWs; all geographic areas; findings considered within social distancing and PPE/handwashing context
Exclude: Masks for prevention of other epidemic viruses (e.g., Ebola) and bacterial infections (e.g., tuberculosis)

Primary Outcome(s)

Infection with SARS-CoV-2, SARS-CoV-1, or MERS-CoV
Influenzalike illness, lab-confirmed viral infection, lab-confirmed influenza, and clinical respiratory illness
Harms of mask usage

Data Extraction (Selection and Coding)

Title and abstract review was performed by one reviewer. A second reviewer verified exclusion decisions. Disagreements were resolved through discussion.

Data was extracted into Excel^® spreadsheets. Data extracted includes author, year, country, study design, study dates, sample size, intervention or exposure characteristics, duration of intervention, population characteristics, and outcomes. Chinese language studies that met inclusion criteria were translated by a Chinese-language speaker.

We calculated risk estimates if they were not reported and data were available. We reversed the direction of the comparisons if necessary for consistency across studies (e.g. so that all studies reported risk estimates as mask use versus non-use, instead of some reporting as mask non-use versus use).

Quality Assessment

For randomized controlled trials, quality was assessed using criteria adapted from the U.S. Preventive Services Task Force (USPSTF).⁵¹ Limitations of observational studies was assessed and summarized using criteria adapted from the USPSTF.

Strategy for Data Synthesis

Data was compiled into evidence tables and synthesized qualitatively. We did not conduct meta-analysis. The strength of evidence was graded for key comparisons and outcomes.

Analysis of Subgroups or Subsets

No formal subgroup analyses were performed. Studies were stratified according to setting (healthcare versus community). For studies conducted in the community, we stratified studies according to whether the mask is worn by someone with infection, someone uninfected, or both.

External Peer Review

One content expert reviewed the draft report.

Appendix B. Evidence Tables

See associated Excel^® files:

Table B-1. Randomized controlled trials of mask use (MS Excel, 37K)
Table B-2. Observational studies of mask use in community settings (MS Excel, 13K)
Table B-3. Observational studies of mask use in healthcare settings (MS Excel, 20K)

Appendix C. Included Studies

Aiello AE, Murray GF, Perez V, et al. Mask use, hand hygiene, and seasonal influenza-like illness among young adults: a randomized intervention trial. J Infect Dis. 2010 Feb 15;201(4):491–8. doi: 10.1086/650396. PMID: 20088690. [PubMed: 20088690] [CrossRef]
Aiello AE, Perez V, Coulborn RM, et al. Facemasks, hand hygiene, and influenza among young adults: a randomized intervention trial. PLoS One. 2012;7(1):e29744. doi: 10.1371/journal.pone.0029744. PMID: 22295066. [PMC free article: PMC3266257] [PubMed: 22295066] [CrossRef]
Alfelali M, Haworth EA, Barasheed O, et al. Facemask versus no facemask in preventing viral respiratory infections during Hajj: a cluster randomised open label trial. March 8, 2019. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3349234.
Alraddadi BM, Al-Salmi HS, Jacobs-Slifka K, et al. Risk Factors for Middle East Respiratory Syndrome Coronavirus Infection among Healthcare Personnel. Emerg Infect Dis. 2016 Nov;22(11):1915–20. doi: 10.3201/eid2211.160920. PMID: 27767011. [PMC free article: PMC5088034] [PubMed: 27767011] [CrossRef]
Barasheed O, Almasri N, Badahdah AM, et al. Pilot randomised controlled trial to test effectiveness of facemasks in preventing influenza-like illness transmission among Australian Hajj pilgrims in 2011. Infect Disord Drug Targets. 2014;14(2):110–6. doi: 10.2174/1871526514666141021112855. PMID: 25336079. [PubMed: 25336079] [CrossRef]
Canini L, Andreoletti L, Ferrari P, et al. Surgical mask to prevent influenza transmission in households: a cluster randomized trial. PLoS One. 2010 Nov 17;5(11):e13998. doi: 10.1371/journal.pone.0013998. PMID: 21103330. [PMC free article: PMC2984432] [PubMed: 21103330] [CrossRef]
Caputo KM, Byrick R, Chapman MG, et al. Intubation of SARS patients: infection and perspectives of healthcare workers. Can J Anaesth. 2006 Feb;53(2):122–9. doi: 10.1007/bf03021815. PMID: 16434750. [PubMed: 16434750] [CrossRef]
Chen WQ, Ling WH, Lu CY, et al. Which preventive measures might protect health care workers from SARS? BMC Public Health. 2009 Mar 13;9:81. doi: 10.1186/1471-2458-9-81. PMID: 19284644. [PMC free article: PMC2666722] [PubMed: 19284644] [CrossRef]
Chughtai AA, Seale H, Dung TC, et al. Compliance with the use of medical and cloth masks among healthcare workers in Vietnam. Ann Occup Hyg. 2016 Jun;60(5):619–30. doi: 10.1093/annhyg/mew008. PMID: 26980847. [PubMed: 26980847] [CrossRef]
Cowling BJ, Chan KH, Fang VJ, et al. Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial. Ann Intern Med. 2009 Oct 6;151(7):437–46. doi: 10.7326/0003-4819-151-7-200910060-00142. PMID: 19652172. [PubMed: 19652172] [CrossRef]
Cowling BJ, Fung RO, Cheng CK, et al. Preliminary findings of a randomized trial of non-pharmaceutical interventions to prevent influenza transmission in households. PLoS One. 2008 May 7;3(5):e2101. doi: 10.1371/journal.pone.0002101. PMID: 18461182. [PMC free article: PMC2364646] [PubMed: 18461182] [CrossRef]
Heinzerling A, Stuckey MJ, Scheuer T, et al. Transmission of COVID-19 to health care personnel during exposures to a hospitalized patient - Solano County, California, February 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 17;69(15):472–6. doi: 10.15585/mmwr.mm6915e5. PMID: 32298249. [PMC free article: PMC7755059] [PubMed: 32298249] [CrossRef]
Larson EL, Ferng YH, Wong-McLoughlin J, et al. Impact of non-pharmaceutical interventions on URIs and influenza in crowded, urban households. Public Health Rep. 2010 Mar-Apr;125(2):178–91. doi: 10.1177/003335491012500206. PMID: 20297744. [PMC free article: PMC2821845] [PubMed: 20297744] [CrossRef]
Lau JT, Lau M, Kim JH, et al. Probable secondary infections in households of SARS patients in Hong Kong. Emerg Infect Dis. 2004 Feb;10(2):235–43. doi: 10.3201/eid1002.030626. PMID: 15030689. [PMC free article: PMC3322902] [PubMed: 15030689] [CrossRef]
Lau JTF, Fung KS, Wong TW, et al. SARS transmission among hospital workers in Hong Kong. Emerg Infect Dis. 2004;10(2):280–6. doi: 10.3201/eid1002.030534. PMID: 15030698. [PMC free article: PMC3322933] [PubMed: 15030698] [CrossRef]
Liu W, Tang F, Fang L-Q, et al. Risk factors for SARS infection among hospital healthcare workers in Beijing: a case control study. Trop Med Int Health. 2009;14(s1):52–9. doi: 10.1111/j.1365-3156.2009.02255.x. [CrossRef]
Loeb M, Dafoe N, Mahony J, et al. Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. JAMA. 2009 Nov 4;302(17):1865–71. doi: 10.1001/jama.2009.1466. PMID: 19797474. [PubMed: 19797474] [CrossRef]
Loeb M, McGeer A, Henry B, et al. SARS among critical care nurses, Toronto. Emerg Infect Dis. 2004 Feb;10(2):251–5. doi: 10.3201/eid1002.030838. PMID: 15030692. [PMC free article: PMC3322898] [PubMed: 15030692] [CrossRef]
Ma HJ, Wang HW, Fang LQ, et al. [A case-control study on the risk factors of severe acute respiratory syndromes among health care workers]. Zhonghua Liu Xing Bing Xue Za Zhi. 2004 Sep;25(9):741–4. PMID: 15555351. [PubMed: 15555351]
MacIntyre CR, Cauchemez S, Dwyer DE, et al. Face mask use and control of respiratory virus transmission in households. Emerg Infect Dis. 2009 Feb;15(2):233–41. doi: 10.3201/eid1502.081167. PMID: 19193267. [PMC free article: PMC2662657] [PubMed: 19193267] [CrossRef]
MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015 Apr 22;5(4):e006577. doi: 10.1136/bmjopen-2014-006577. PMID: 25903751. [PMC free article: PMC4420971] [PubMed: 25903751] [CrossRef]
MacIntyre CR, Wang Q, Cauchemez S, et al. A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza Other Respir Viruses. 2011 May;5(3):170–9. doi: 10.1111/j.1750-2659.2011.00198.x. PMID: 21477136. [PMC free article: PMC4941587] [PubMed: 21477136] [CrossRef]
MacIntyre CR, Wang Q, Seale H, et al. A randomized clinical trial of three options for N95 respirators and medical masks in health workers. Am J Respir Crit Care Med. 2013 May 1;187(9):960–6. doi: 10.1164/rccm.201207-1164OC. PMID: 23413265. [PubMed: 23413265] [CrossRef]
MacIntyre CR, Zhang Y, Chughtai AA, et al. Cluster randomised controlled trial to examine medical mask use as source control for people with respiratory illness. BMJ Open. 2016 Dec 30;6(12):e012330. doi: 10.1136/bmjopen-2016-012330. PMID: 28039289. [PMC free article: PMC5223715] [PubMed: 28039289] [CrossRef]
Nishiura H, Kuratsuji T, Quy T, et al. Rapid awareness and transmission of severe acute respiratory syndrome in Hanoi French Hospital, Vietnam. Am J Trop Med Hyg. 2005 Jul;73(1):17–25. PMID: 16014825. [PubMed: 16014825]
Nishiyama A, Wakasugi N, Kirikae T, et al. Risk factors for SARS infection within hospitals in Hanoi, Vietnam. Jpn J Infect Dis. 2008 Sep;61(5):388–90. PMID: 18806349. [PubMed: 18806349]
Pei LY, Gao ZC, Yang Z, et al. [Investigation of the influencing factors on severe acute respiratory syndrome among health care workers]. Beijing Da Xue Xue Bao Yi Xue Ban. 2006 Jun 18;38(3):271–5. PMID: 16778970. [PubMed: 16778970]
Raboud J, Shigayeva A, McGeer A, et al. Risk factors for SARS transmission from patients requiring intubation: a multicentre investigation in Toronto, Canada. PLoS One. 2010 May 19;5(5):e10717. doi: 10.1371/journal.pone.0010717. PMID: 20502660. [PMC free article: PMC2873403] [PubMed: 20502660] [CrossRef]
Radonovich LJ, Jr., Simberkoff MS, Bessesen MT, et al. N95 Respirators vs medical masks for preventing influenza among health care personnel: a randomized clinical trial. JAMA. 2019 Sep 3;322(9):824–33. doi: 10.1001/jama.2019.11645. PMID: 31479137. [PMC free article: PMC6724169] [PubMed: 31479137] [CrossRef]
Seto WH, Tsang D, Yung RW, et al. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). Lancet. 2003 May 3;361(9368):1519–20. doi: 10.1016/s0140-6736(03)13168-6. PMID: 12737864. [PMC free article: PMC7112437] [PubMed: 12737864] [CrossRef]
Simmerman JM, Suntarattiwong P, Levy J, et al. Findings from a household randomized controlled trial of hand washing and face masks to reduce influenza transmission in Bangkok, Thailand. Influenza Other Respir Viruses. 2011 Jul;5(4):256–67. doi: 10.1111/j.1750-2659.2011.00205.x. PMID: 21651736. [PMC free article: PMC4634545] [PubMed: 21651736] [CrossRef]
Scales DC, Green K, Chan AK, et al. Illness in intensive care staff after brief exposure to severe acute respiratory syndrome. Emerg Infect Dis. 2003 Oct;9(10):1205–10. doi: 10.3201/eid0910.030525. PMID: 14609453. [PMC free article: PMC3033076] [PubMed: 14609453] [CrossRef]
Suess T, Remschmidt C, Schink SB, et al. The role of facemasks and hand hygiene in the prevention of influenza transmission in households: results from a cluster randomised trial; Berlin, Germany, 2009-2011. BMC Infect Dis. 2012 Jan 26;12:26. doi: 10.1186/1471-2334-12-26. PMID: 22280120. [PMC free article: PMC3285078] [PubMed: 22280120] [CrossRef]
Teleman MD, Boudville IC, Heng BH, et al. Factors associated with transmission of severe acute respiratory syndrome among health-care workers in Singapore. Epidemiol Infect. 2004 Oct;132(5):797–803. doi: 10.1017/s0950268804002766. PMID: 15473141. [PMC free article: PMC2870165] [PubMed: 15473141] [CrossRef]
Tuan PA, Horby P, Dinh PN, et al. SARS transmission in Vietnam outside of the health-care setting. Epidemiol Infect. 2007 Apr;135(3):392–401. doi: 10.1017/s0950268806006996. PMID: 16870029. [PMC free article: PMC2870589] [PubMed: 16870029] [CrossRef]
Wang X, Pan Z, Cheng Z. Association between 2019-nCoV transmission and N95 respirator use. J Hosp Infect. 2020(March 3)doi: 10.1016/j.jhin.2020.02.021. [PMC free article: PMC7134426] [PubMed: 32142885] [CrossRef]
Wilder-Smith A, Teleman MD, Heng BH, et al. Asymptomatic SARS coronavirus infection among healthcare workers, Singapore. Emerg Infect Dis. 2005 Jul;11(7):1142–5. doi: 10.3201/eid1107.041165. PMID: 16022801. [PMC free article: PMC3371799] [PubMed: 16022801] [CrossRef]
Wu J, Xu F, Zhou W, et al. Risk factors for SARS among persons without known contact with SARS patients, Beijing, China. Emerg Infect Dis. 2004;10(2):210–6. doi: 10.3201/eid1002.030730. PMID: 15030685. [PMC free article: PMC3322931] [PubMed: 15030685] [CrossRef]
Yin WW, Gao LD, Lin WS, et al. [Effectiveness of personal protective measures in prevention of nosocomial transmission of severe acute respiratory syndrome]. Zhonghua Liu Xing Bing Xue Za Zhi. 2004 Jan;25(1):18–22. PMID: 15061941. [PubMed: 15061941]

Appendix D. Risk of Bias Assessments

Author, Year	Randomization	Allocation Concealment	Baseline Groups Comparable	Blinding of Study Participants	Blinding of Outcomes Assessment	Attrition and Missing Data Reported	Attrition and Missing Data	Intention-To-Treat Analysis	Analysis for Adherence	Cluster Trials: Adjustment for Clustering	Overall Quality Rating
Aiello A, 2010⁸	Yes	Yes	Yes	No	Unclear	Yes	7.6% (99/1,297) loss to followup	Yes	Yes	Yes	Good
Aiello A, 2012⁹	Yes	Yes	Yes	No	Yes	Yes	6.1% loss to followup	Yes	Yes	Yes	Good
Alfelali M, 2019¹⁰	Yes	Unclear	Yes	No	Yes for laboratory outcomes	Yes	5.8% did not return their health diaries	Yes	Yes	Yes	Good
Barasheed O, 2014¹²	Yes	Unclear	No	No	No	Yes	None reported	Yes	Yes	No	Fair
Canini L, 2010¹³	Yes	Yes	Yes	No	Yes for laboratory outcomes	Yes	Two households were loss to followup	Yes	Yes	Yes	Good
Chughtai A, 2016¹⁶	Yes	Unclear	Unclear	No	No	Yes	For adverse event outcomes, 19 missing data	No	Yes	Yes	Fair
Cowling BJ, 2008¹⁸	Yes	Yes	No	No	Yes for laboratory outcomes	Yes	35% (70/198) withdrew or could not be contacted	Yes	Yes	Yes	Fair
Cowling BJ, 2009¹⁷	Yes	Yes	No	No	Yes for laboratory outcomes	Yes	21% (85/407) households withdrew or could not be contacted	Yes	Yes	Yes	Fair
Larson EL, 2010²⁰	Yes	Unclear	No	No	Unclear	Yes	18% (108/617) withdrew consent or were lost to followup; 13% (66/509) dropped out	Unclear	Yes	NA	Fair
Loeb M, 2009²⁴	Yes	No	Yes	No	Yes for laboratory outcomes	Yes	5% (24/446) withdrew prior to followup	Yes	Yes	NA	Good
MacIntyre C, 2009²⁷	Yes	No	Yes	No	Yes for laboratory outcomes	Yes	1% (2/145) lost to f/u	Yes	Yes	Yes	Good
MacIntyre C, 2011²⁹	Yes	Unclear	No	No	Unclear	Yes	None reported	Yes	Yes	Yes	Fair
MacIntyre C, 2013³⁰	Unclear	Unclear	No	No	Unclear	Yes	None reported	Yes	Yes	Yes	Fair
MacIntyre C, 2015²⁸	Yes	Unclear	Yes	No	Yes for laboratory outcomes	Yes	None reported	Yes	Yes	Yes	Good
MacIntyre C, 2016³¹	Yes	Unclear	Yes	No	Yes for laboratory outcomes	Yes	None reported	Yes	Yes	Yes	Good
Radonovich L, 2019³⁶	Yes	Yes	Yes	No	Yes	Yes	17% (491/2862) withdrew or excluded	Yes	Yes	Yes	Good
Simmerman J, 2011³⁸	Yes	Unclear	Yes	No	Unclear	Yes	4.9% (23/465) excluded from analysis	No	Yes	Yes	Good
Suess T, 2012³⁹	Yes	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	Good

Appendix E. Ongoing Studies

NCT Number	Title	Population, Interventions, Condition, Outcomes (PICOs)	Anticipated Primary Completion Date
NCT04337541	Reduction in COVID-19 Infection Using Surgical Facial Masks Outside the Healthcare System	Population People working outside of their home, who have not previously been infected with COVID-19 and who do not wear facial masks (e.g., healthcare personnel) when working. Interventions Surgical facial mask No mask Condition COVID-19 Outcomes Reduction in COVID-19 infection frequency	July 2020
NCT04336215	Cohort Study of SARS-CoV-2 Incidence, Transmission, and Disease Severity in Healthcare Workers	Population Healthcare workers from two hospitals in New Brunswick and Newark, NJ Non-healthcare workers from Rutgers faculty, staff, and hospital employees without patient contact Household members of participants who contract SARS-CoV-2 during the study period Interventions Not applicable Condition SARS-CoV-2 infection Outcomes Prevalence and incidence of infection	September 2020
NCT04362267	Incidence of SARS-Cov2 Infection Among HCW in Lille University Hospital	Population Healthdare workers with COVID-19 high exposure during care activities Interventions Self-administered questionnaire Condition COVID-19 Outcomes Incidence of SARS- Cov2 infection heathcare worker diagnosed by the positivity of SARS-Cov2 reverse transcription polymerase chain reaction (RT-PCR) and serological testing Risk of infection based on occupational and environmental exposures	September 2020
NCT04296643	Medical Masks Versus N95 Respirators to Prevent 2019 Novel Coronavirus Disease (COVID-19) in Healthcare Workers: A Randomized Trial	Population Nurses who work > 37 hours per week in medical, emergency, pediatric units Interventions N95 respirator Medical mask Condition COVID-19 Outcomes Number of participants with reverse transcription polymerase chain reaction (RT-PCR) confirmed COVID-19 infection	December 2020
NCT04342884	A Multicenter, Prospective Study of COVID-19 Using Real-Time Syndromic Surveillance, Scheduled At-home Serologic Testing, and Electronic Health Records	Population Clients of Wake Forest Baptist Health Healthcare workers of Wake Forest Baptist Health Interventions Not reported Condition SARS-CoV-2 infection and COVID-19 Outcomes (selected) Seroprevalence of SARS-CoV-2 infection among healthcare workers of North Carolina Stratified incidence of SARS-CoV-2 infection by use of personal protective equipment (PPE) by health workers Relative risk of SARS-CoV-2 infection by use of PPE by healthcare workers	December 2021

Report References

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2.: U.S. Centers for Disease Control. Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings. 2020. https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html. Accessed April 15 2020.
3.: World Health Organization. Shortage of personal protective equipment endangering health workers worldwide. 2020. https://www.who.int/news-room/detail/03-03-2020-shortage-of-personal-protective-equipment-endangering-health-workers-worldwide. Accessed April 15 2020.
4.: ECRI. Clinical Evidence Assessment: Safety of Extended Use and Reuse of N95 Respirators. 2020. https://assets.ecri.org/PDF/COVID-19-Resource-Center/COVID-19-Clinical-Care/COVID-ECRI-N95-Respirators-updated.pdf. Accessed April 10 2020.
5.: U.S. Centers for Disease Control. Decontamination and Reuse of Filtering Facepiece Respirators. 2020. https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html. Accessed April 15 2020.
6.: World Health Organization. Global research on coronavirus disease (COVID-19) database. 2020. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/global-research-on-novel-coronavirus-2019-ncov. Accessed March 30, 2020.
7.: Cold Spring Harbor Laboratory. medRxiv: The Preprint Server of Health Sciences. https://www.medrxiv.org/. Accessed March 30, 2020.
8.: Aiello AE, Murray GF, Perez V, et al. Mask use, hand hygiene, and seasonal influenza-like illness among young adults: a randomized intervention trial. J Infect Dis. 2010 Feb 15;201(4):491–8. doi: 10.1086/650396. PMID: 20088690. [PubMed: 20088690] [CrossRef]
9.: Aiello AE, Perez V, Coulborn RM, et al. Facemasks, hand hygiene, and influenza among young adults: a randomized intervention trial. PLoS One. 2012;7(1):e29744. doi: 10.1371/journal.pone.0029744. PMID: 22295066. [PMC free article: PMC3266257] [PubMed: 22295066] [CrossRef]
10.: Alfelali M, Haworth EA, Barasheed O, et al. Facemask versus no facemask in preventing viral respiratory infections during Hajj: a cluster randomised open label trial. March 8, 2019. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3349234.
11.: Alraddadi BM, Al-Salmi HS, Jacobs-Slifka K, et al. Risk factors for Middle East respiratory syndrome coronavirus infection among healthcare personnel. Emerg Infect Dis. 2016 Nov;22(11):1915–20. doi: 10.3201/eid2211.160920. PMID: 27767011. [PMC free article: PMC5088034] [PubMed: 27767011] [CrossRef]
12.: Barasheed O, Almasri N, Badahdah AM, et al. Pilot randomised controlled trial to test effectiveness of facemasks in preventing influenza-like illness transmission among Australian Hajj pilgrims in 2011. Infect Disord Drug Targets. 2014;14(2):110–6. doi: 10.2174/1871526514666141021112855. PMID: 25336079. [PubMed: 25336079] [CrossRef]
13.: Canini L, Andreoletti L, Ferrari P, et al. Surgical mask to prevent influenza transmission in households: a cluster randomized trial. PLoS One. 2010 Nov 17;5(11):e13998. doi: 10.1371/journal.pone.0013998. PMID: 21103330. [PMC free article: PMC2984432] [PubMed: 21103330] [CrossRef]
14.: Caputo KM, Byrick R, Chapman MG, et al. Intubation of SARS patients: infection and perspectives of healthcare workers. Can J Anaesth. 2006 Feb;53(2):122–9. doi: 10.1007/bf03021815. PMID: 16434750. [PubMed: 16434750] [CrossRef]
15.: Chen WQ, Ling WH, Lu CY, et al. Which preventive measures might protect health care workers from SARS? BMC Public Health. 2009 Mar 13;9:81. doi: 10.1186/1471-2458-9-81. PMID: 19284644. [PMC free article: PMC2666722] [PubMed: 19284644] [CrossRef]
16.: Chughtai AA, Seale H, Dung TC, et al. Compliance with the use of medical and cloth masks among healthcare workers in Vietnam. Ann Occup Hyg. 2016 Jun;60(5):619–30. doi: 10.1093/annhyg/mew008. PMID: 26980847. [PubMed: 26980847] [CrossRef]
17.: Cowling BJ, Chan KH, Fang VJ, et al. Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial. Ann Intern Med. 2009 Oct 6;151(7):437–46. doi: 10.7326/0003-4819-151-7-200910060-00142. PMID: 19652172. [PubMed: 19652172] [CrossRef]
18.: Cowling BJ, Fung RO, Cheng CK, et al. Preliminary findings of a randomized trial of non-pharmaceutical interventions to prevent influenza transmission in households. PLoS One. 2008 May 7;3(5):e2101. doi: 10.1371/journal.pone.0002101. PMID: 18461182. [PMC free article: PMC2364646] [PubMed: 18461182] [CrossRef]
19.: Heinzerling A, Stuckey MJ, Scheuer T, et al. Transmission of COVID-19 to health care personnel during exposures to a hospitalized patient - Solano County, California, February 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 17;69(15):472–6. doi: 10.15585/mmwr.mm6915e5. PMID: 32298249. [PMC free article: PMC7755059] [PubMed: 32298249] [CrossRef]
20.: Larson EL, Ferng YH, Wong-McLoughlin J, et al. Impact of non-pharmaceutical interventions on URIs and influenza in crowded, urban households. Public Health Rep. 2010 Mar-Apr;125(2):178–91. doi: 10.1177/003335491012500206. PMID: 20297744. [PMC free article: PMC2821845] [PubMed: 20297744] [CrossRef]
21.: Lau JT, Lau M, Kim JH, et al. Probable secondary infections in households of SARS patients in Hong Kong. Emerg Infect Dis. 2004c Feb;10(2):235–43. doi: 10.3201/eid1002.030626. PMID: 15030689. [PMC free article: PMC3322902] [PubMed: 15030689] [CrossRef]
22.: Lau JTF, Fung KS, Wong TW, et al. SARS transmission among hospital workers in Hong Kong. Emerg Infect Dis. 2004b;10(2):280–6. doi: 10.3201/eid1002.030534. PMID: 15030698. [PMC free article: PMC3322933] [PubMed: 15030698] [CrossRef]
23.: Liu W, Tang F, Fang L-Q, et al. Risk factors for SARS infection among hospital healthcare workers in Beijing: a case control study. Trop Med Int Health. 2009;14(s1):52–9. doi: 10.1111/j.1365-3156.2009.02255.x. [CrossRef]
24.: Loeb M, Dafoe N, Mahony J, et al. Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. JAMA. 2009 Nov 4;302(17):1865–71. doi: 10.1001/jama.2009.1466. PMID: 19797474. [PubMed: 19797474] [CrossRef]
25.: Loeb M, McGeer A, Henry B, et al. SARS among critical care nurses, Toronto. Emerg Infect Dis. 2004 Feb;10(2):251–5. doi: 10.3201/eid1002.030838. PMID: 15030692. [PMC free article: PMC3322898] [PubMed: 15030692] [CrossRef]
26.: Ma HJ, Wang HW, Fang LQ, et al. [A case-control study on the risk factors of severe acute respiratory syndromes among health care workers]. Zhonghua Liu Xing Bing Xue Za Zhi. 2004 Sep;25(9):741–4. PMID: 15555351. [PubMed: 15555351]
27.: MacIntyre CR, Cauchemez S, Dwyer DE, et al. Face mask use and control of respiratory virus transmission in households. Emerg Infect Dis. 2009 Feb;15(2):233–41. doi: 10.3201/eid1502.081167. PMID: 19193267. [PMC free article: PMC2662657] [PubMed: 19193267] [CrossRef]
28.: MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015 Apr 22;5(4):e006577. doi: 10.1136/bmjopen-2014-006577. PMID: 25903751. [PMC free article: PMC4420971] [PubMed: 25903751] [CrossRef]
29.: MacIntyre CR, Wang Q, Cauchemez S, et al. A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza Other Respir Viruses. 2011 May;5(3):170–9. doi: 10.1111/j.1750-2659.2011.00198.x. PMID: 21477136. [PMC free article: PMC4941587] [PubMed: 21477136] [CrossRef]
30.: MacIntyre CR, Wang Q, Seale H, et al. A randomized clinical trial of three options for N95 respirators and medical masks in health workers. Am J Respir Crit Care Med. 2013 May 1;187(9):960–6. doi: 10.1164/rccm.201207-1164OC. PMID: 23413265. [PubMed: 23413265] [CrossRef]
31.: MacIntyre CR, Zhang Y, Chughtai AA, et al. Cluster randomised controlled trial to examine medical mask use as source control for people with respiratory illness. BMJ Open. 2016 Dec 30;6(12):e012330. doi: 10.1136/bmjopen-2016-012330. PMID: 28039289. [PMC free article: PMC5223715] [PubMed: 28039289] [CrossRef]
32.: Nishiura H, Kuratsuji T, Quy T, et al. Rapid awareness and transmission of severe acute respiratory syndrome in Hanoi French Hospital, Vietnam. Am J Trop Med Hyg. 2005 Jul;73(1):17–25. PMID: 16014825. [PubMed: 16014825]
33.: Nishiyama A, Wakasugi N, Kirikae T, et al. Risk factors for SARS infection within hospitals in Hanoi, Vietnam. Jpn J Infect Dis. 2008 Sep;61(5):388–90. PMID: 18806349. [PubMed: 18806349]
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Version 2.0

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Chou R, Dana T, Jungbauer R, Weeks C, McDonagh M. Masks for Prevention of COVID-19 in Community and Healthcare Settings. Version 2. Rapid Evidence Product. (Prepared by the Pacific Northwest Evidence-based Practice Center under Contract No. 290-2015-00009-I). AHRQ Publication No. 20-EHC019. Rockville, MD: Agency for Healthcare Research and Quality. June 2020. Posted final reports are located on the Effective Health Care Program search page. DOI: https://doi.org/10.23970/AHRQEPCCOVIDMASKS2.

Disclaimers: This report is based on research conducted by the Pacific Northwest Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (AHRQ), Rockville, MD (Contract No. 290-2015-00009-I). The findings and conclusions in this document are those of the authors, who are responsible for its contents; the findings and conclusions do not necessarily represent the views of AHRQ. Therefore, no statement in this report should be construed as an official position of AHRQ or of the U.S. Department of Health and Human Services.

None of the investigators have any affiliations or financial involvement that conflicts with the material presented in this report.

The information in this report is intended to help health care decision makers—patients and clinicians, health system leaders, and policymakers, among others—make well-informed decisions and thereby improve the quality of health care services. This report is not intended to be a substitute for the application of clinical judgment. Anyone who makes decisions concerning the provision of clinical care should consider this report in the same way as any medical reference and in conjunction with all other pertinent information, i.e., in the context of available resources and circumstances presented by individual patients.

This report is made available to the public under the terms of a licensing agreement between the author and the Agency for Healthcare Research and Quality. This report may be used and reprinted without permission except those copyrighted materials that are clearly noted in the report. Further reproduction of those copyrighted materials is prohibited without the express permission of copyright holders.

AHRQ or U.S. Department of Health and Human Services endorsement of any derivative products that may be developed from this report, such as clinical practice guidelines, other quality enhancement tools, or reimbursement or coverage policies, may not be stated or implied.

AHRQ appreciates appropriate acknowledgment and citation of its work. Suggested language for acknowledgment: This work was based on an evidence report, Masks for Prevention of COVID-19 in Community and Healthcare Settings, Version 2, by the Evidence-based Practice Center Program at the Agency for Healthcare Research and Quality (AHRQ).

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Chou R, Dana T, Jungbauer R, et al. Masks for Prevention of COVID-19 in Community and Healthcare Settings [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2020 Jun 24.
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Masks for Prevention of COVID-19 in Community and Healthcare Settings

Background and Purpose

Key Questions

Evidence Summary

Methods

Evidence Base

KQ 1. What is the effectiveness of respirators (e.g. N95) versus facemasks (surgical) versus cloth masks for prevention of COVID-19 in addition to standard precautions (gowns + gloves + handwashing)?

Community Settings

Healthcare Settings

Harms

Key Question 2. What is the evidence for extended or reuse of N95 respirators for prevention of COVID-19?

Conclusions and Future Research

Figure 1

Table 1

Glossary

Afterword

Appendix A. Methods

Searches

Search Strategies

Key Question 1

Randomized Controlled Trials

PubMed MEDLINE

Elsevier Embase

Observational Studies

Elsevier Embase

Key Question 2

PubMed MEDLINE

Elsevier Embase

Types of Studies Included

PICOTS

Participants/Population

Intervention/Exposure

Comparator/Control

Context

Primary Outcome(s)

Data Extraction (Selection and Coding)

Quality Assessment

Strategy for Data Synthesis

Analysis of Subgroups or Subsets

External Peer Review

Appendix B. Evidence Tables

Appendix C. Included Studies

Appendix D. Risk of Bias Assessments

Appendix E. Ongoing Studies

Report References

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