COVID-19 Evidence Alerts
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Current best evidence for clinical care (more info)

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Primary Prevention Bartoszko JJ, Farooqi MAM, Alhazzani W, et al. Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: A systematic review and meta-analysis of randomized trials. Influenza Other Respir Viruses. 2020 Jul;14(4):365-373. doi: 10.1111/irv.12745. Epub 2020 Apr 21.

BACKGROUND: Respiratory protective devices are critical in protecting against infection in healthcare workers at high risk of novel 2019 coronavirus disease (COVID-19); however, recommendations are conflicting and epidemiological data on their relative effectiveness against COVID-19 are limited.

PURPOSE: To compare medical masks to N95 respirators in preventing laboratory-confirmed viral infection and respiratory illness including coronavirus specifically in healthcare workers.

DATA SOURCES: MEDLINE, Embase, and CENTRAL from January 1, 2014, to March 9, 2020. Update of published search conducted from January 1, 1990, to December 9, 2014.

STUDY SELECTION: Randomized controlled trials (RCTs) comparing the protective effect of medical masks to N95 respirators in healthcare workers.

DATA EXTRACTION: Reviewer pair independently screened, extracted data, and assessed risk of bias and the certainty of the evidence.

DATA SYNTHESIS: Four RCTs were meta-analyzed adjusting for clustering. Compared with N95 respirators; the use of medical masks did not increase laboratory-confirmed viral (including coronaviruses) respiratory infection (OR 1.06; 95% CI 0.90-1.25; I2  = 0%; low certainty in the evidence) or clinical respiratory illness (OR 1.49; 95% CI: 0.98-2.28; I2  = 78%; very low certainty in the evidence). Only one trial evaluated coronaviruses separately and found no difference between the two groups (P = .49).

LIMITATIONS: Indirectness and imprecision of available evidence.

CONCLUSIONS: Low certainty evidence suggests that medical masks and N95 respirators offer similar protection against viral respiratory infection including coronavirus in healthcare workers during non-aerosol-generating care. Preservation of N95 respirators for high-risk, aerosol-generating procedures in this pandemic should be considered when in short supply.

Discipline / Specialty Area Score
Emergency Medicine
Infectious Disease
Hemostasis and Thrombosis
Intensivist/Critical Care
General Internal Medicine-Primary Care(US)
Occupational and Environmental Health
Public Health
Family Medicine (FM)/General Practice (GP)
Pediatrics (General)
Surgery - General
Hospital Doctor/Hospitalists
Internal Medicine
Comments from MORE raters

Anesthesiology rater

Great title but unfortunately this review was based on very limited and mostly irrelevant data.

Cardiology rater

Low-certainty evidence suggests that medical masks and N95 respirators offer similar protection against viral respiratory infection, including coronavirus, in healthcare workers during nonaerosol-generating care.

Emergency Medicine rater

With ongoing concerns, this provides some support that surgical masks are not inferior to N95 when dealing with potential (viral) infectious patients. Since there were only a few studies, however, and the point estimate did trend toward N95 being superior, this may not completely allay the fear for those who don`t feel comfortable with just a surgical mask.

Emergency Medicine rater

Useful study that may influence physicians to use N95 mask only in high-risk activities.

Emergency Medicine rater

This is a meta-analysis asking the question: In health care workers exposed to patients (non-aerosol generating) with viral infections (including coronaviruses), do N95 masks compared with regular medical masks result in decreased viral transmission? This is an update of a previous 2016 study. The search was extensive. Of the four studies found, all randomized controlled trials, all had a lack of blinding (unavoidable), inconsistency, and indirectness. The results show no difference between masks in terms of laboratory-confirmed viral respiratory infection or clinical respiratory illness.

Family Medicine (FM)/General Practice (GP) rater

I guess this is reassuring, although authors do state the evidence is low certainty. Much of it not specifically about COVID 19 virus. I do note they combined fitted and non-fitted data for N95, which could have affected the outcome.

General Internal Medicine-Primary Care(US) rater

I found this distressing. First, the title implies that it addresses COVID-19 when in fact it does not. It does mention common coronaviruses, but based on the clinical difference from COVID, I would not presume to equate the two. There are not even any trials that address SARS or MERS, which might at least have been somewhat more relevant. Presumably, the authors feel the title will attract interest. Second, this analysis added only 1 new trial to a previous metanalysis, which hardly seems like it would add any new information, especially since that article published in 2019 was from a trial in 2011-2014. Third, as the authors admit, the strength of evidence is low and the risk of bias is high, so even if my previous comments were not relevant, this would make any interpretation of the data in these trials unusable in practice.

Geriatrics rater

Interesting article but I'm not sure the authors answered the question of whether medical masks are equivalent to N95s in preventing or decreasing the transmission of COVID-19. Given the lethality of this novel coronavirus, I would not want to guess about the effectiveness. Doing a randomized controlled trial to address this may be considered unethical.

Geriatrics rater

Interesting study showing the data, or mostly the lack thereof, that N95 respirators are superior to standard masks. It is unclear whether anyone will act based on this, but it would provide some justification for conducting an RCT in areas where supply is limited.

Gynecology rater

While the pertinence of this particular manuscript may initially appear irrelevant to OB/GYN providers, the details included in this paper are indeed relevant to all healthcare providers. The meta-analysis described shows a real-world comparison of the effectiveness of the general surgical mask and the N95 respirator when caring for SARS2 patients. The conclusions are relevant for any policy-generating decision-maker, as is the quality of the statistics-gathering of the review.

Gynecology rater

This is a great and timely review of the available data. There is so much angst and confusion about this topic that leads to a lot of frustration, including among healthcare workers. It's also a good reminder that more studies need to be done due to the limitation of the evidence to date.

Hemostasis and Thrombosis rater

A well-done synthesis of the "best" there is of low- and very low-quality data; no COVID-19 studies included.

Hospital Doctor/Hospitalists rater

This article is noteworthy mostly because many folks will be interested in the topic. The authors performed a well-structured and well-documented analysis. The problem is that the data were limited, the quality of the studies was not high, and the risk for bias was high. On balance, this won't change the world, but it is important and should be reported.

Infectious Disease rater

This information is relevant for the safety of healthcare workers (HCW) in the current Covid-19 pandemic. With uncertainty regarding what PPE is sufficient for HCW safety, there are conflicting data available. With aerosol vs droplet as the mode of transmission for Covid-19, N95 vs surgical masks have been proposed. This paper adds to the body of science in this regard and lends support to the prevailing guidelines.

Infectious Disease rater

This review confirms the usefulness of regular masks in preventing respiratory infections and the reasoning for reserving use of N95 masks for highest-risk situations.

Intensivist/Critical Care rater

Important article. There is a high likelihood of confounding due to low-quality evidence. Worthy of highlighting with caveats.

Internal Medicine rater

The authors in this study redo a meta-analysis already done in 2016 in which in N95 masks and simple surgical masks are compared for respiratory illness. I have a huge problem with this manuscript in that reading only the title could lead someone to conclude these studies were done in COVID-19. While I completely agree there are very many similarities in respiratory illnesses, we do not yet know whether the aerosolized particles of COVID are potentially disease-generating. If it turns out that all corona viruses share similar infectivity, I think this study could be extrapolated. Until this is clarified, or unless the authors clearly make this distinction, I do not believe this is something that I would share with my hospitalist colleagues.

Internal Medicine rater

Useful summary of trials on use of regular masks versus N95 masks in preventing respiratory viral illnesses.

Nephrology rater

Although this study is highly relevant in the current Covid-19 pandemic, the low certainty makes it less useful. Surgical masks vs N95 masks have not been tested against SARS-CoV-2, and since many healthcare workers have already died from Covid-19 in many countries, I doubt a recommendation to not wear N95 masks will be accepted by exposed workers. Even in general care, you don't know when a patient will suddenly start coughing at you.

Obstetrics rater

Critically important information during this pandemic, but sad that there is a shortage of N95 masks.

Obstetrics rater

Less than optimum level of evidence but a worthwhile and clinically relevant study in view of the current pandemic.

Occupational and Environmental Health rater

A robustly conducted meta-anlaysis attempting to clarify a very important current issue. I worry that while it might be newsworthy, non-EBM individuals might look to the conclusions rather than the authors' own assessment of the uncertainty of the data. Observational data are likely quite confounded by indication, so the authors' decision to utilize only RCTs, while limited by the small number of studies, is also likely to provide the least biased answer.

Pediatrics (General) rater

A systemic review comparing N-95 with simple medical masks for prevention of respiratory viral infections was done. Most of the studies were of general respiratory viruses or influenza. Simple medical masks appear to be equally effective in prevention infection in exposed health care workers. However, this is based on low-quality evidence. Rated low in newsworthiness because this information is being widely disseminated by various country, provincial and state health care departments.

Public Health rater

Major limitations - small number of studies. Authors reported that, "There is no convincing evidence that medical masks are inferior to N95 respirators for protecting healthcare workers against laboratory-confirmed viral respiratory infections during routine care and non–aerosol-generating procedures." Recent data show that SARS-CoV-2 remains viable in aerosols. Thus, it would be difficult to generalize these findings to Covid-19.

Public Health rater

Useful information. Most practitioners in my discipline probably don't know this, unless they have kept up-to-date with this issue.

Surgery - General rater

Low-quality review that did not yield scientifically sound data. It also did not discuss "out of the box" information that can better direct the readership, such as RZm2 masks.

Surgery - General rater

Good to have confirmation that in Canada we are following a policy for which there is fair evidence of safety for healthcare providers.

Surgery - General rater

This meta-analysis is highly relevant at this time when shortages of PPE lead to re-use of medical masks and a perception that N-95 masks are needed for routine care. The article provides confidence that routine masks provide adequate protection and filtration for all duties excluding aerosol generating procedures such as intubation or endoscopy. This should help triage appropriate supplies to those practitioners that need them most urgently.