Systematic review registration
This systematic review was registered with number CRD42020179966 (https://www.crd.york.ac.uk/PROSPERO)
Search strategy
Articles published in English from January 1994 to January 2020 which explored the relationship between wearing medical masks and protection against respiratory infectious diseases were retrieved from PubMed, EMBASE, Cochrane CENTRAL, and Web of Science databases. The following search terms were used: “Respiratory infectious diseases”, “COVID-19”, “respiratory tract infection”, “prevention”, “Medical masks” and “N95 respirators”. Logical operators (OR, NOT, AND) were used to combine keywords and subject words (Table 1).
Inclusion criteria
Articles that met the following criteria were selected: This study design was peer-reviewed randomized controlled trials (RCTs) or observational studies (OSs); The population was medical staff; The exposure of interest was wearing medical masks or N95 respirators; The outcome of interest was the proportion of medical mask use in the experimental and control groups; The settings were healthcare settings worldwide.
Exclusion criteria
We excluded guidelines, editorials, public press articles, reviews, raw data unavailable, theoretical models and the articles published in languages other than English.
Table 1. Search strings for the four databases
Database
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Search string
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PubMed
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(masks*[MeSH Terms] OR mask*[Title/Abstract] OR N95 respirators*[Title/Abstract] OR “ medical masks”[Title/Abstract] OR “face masks”[Title/Abstract] OR “medical mask”[Title/Abstract] OR “medical masks”[Title/Abstract] OR “surgical mask”[Title/Abstract] OR “surgical masks”[Title/Abstract] OR “surgical facemask”[Title/Abstract] OR “surgical facemasks”[Title/Abstract] OR “surgical face mask”[Title/Abstract] OR “surgical face masks”[Title/Abstract] OR respiratory infectious diseases[Title/Abstract] OR COVID-19[Title/Abstract] OR prevention[Title/Abstract] OR control[Title/Abstract] OR measur[Title/Abstract] OR evaluat[Title/Abstract] OR effect[Title/Abstract] OR Public Health[Title/Abstract] OR medical workers[Title/Abstract]
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EMBASE
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(‘espiratory infectious diseases’:ab,ti OR ‘COVID-19’:ab,ti) AND (‘Public Health*’:ab,ti OR ‘medical workers*’:ab,ti OR ‘nursing home patient’:ab,ti) AND (‘prevention’:ab,ti OR ‘control*’:ab,ti OR ‘measure*’:ab,ti OR ‘evaluate*’:ab,ti OR ‘effect*’:ab,ti OR ‘prevent*’:ab,ti OR ‘control*’:ab,ti OR ‘intervention*’:ab,ti OR ‘outcome*’:ab,ti)
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Web of Science
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TS=(mask* OR facemask* OR “face mask“ OR “face masks“ OR “medical“ OR “medical mask“ OR “medical masks“ OR “medical facemask“ OR “medical facemasks“ OR “medical face mask“ OR “medical face masks“ OR “N95“ OR “N95 respirators“ OR “surgical facemask“ OR “surgical facemasks“ OR “surgical face mask“ OR “surgical face masks“ OR Infectious Diseases OR Respiratory infectious diseases OR “COVID-19“ OR “prevention“ OR “control“ OR “prevention and control“ OR PPE OR “measur“ OR “evaluat“ OR “effect“ OR “Public Health“ OR “medical workers“ ) AND TS=( “healthcare worker” OR “healthcare workers” OR “health care worker” OR “health care workers” OR “health-care worker” OR “health-care workers” OR “healthcare professional” OR “healthcare professionals” OR “health care professional” OR “health care professionals” OR “health-care professional” OR “health-care professionals” OR staff OR “healthcare personnel” OR “health care personnel” OR “health-care personnel”)
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Cochrane CENTRAL
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Respiratory infectious diseases OR COVID-19 in Title, Abstract, Keywords, AND ‘medical masks’ OR ‘N95 respirators’ OR ‘mask’ in Title, Abstract, Keywords, AND practice OR control* OR measur* OR evaluat* OR effect* OR prevent* OR prevention and control* OR intervention* OR outcome* in Title, Abstract, Keywords,, Publication Year from 1994 to 2020 in Trials
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Data extraction
Data extraction was conducted in two stages: first, the literature was screened by two researchers according to inclusion criteria. The screened literature was then searched and evaluated by two other researchers according to the inclusion criteria and exclusion criteria. To avoid errors, a pre-designed form was used to select the study characteristics, baseline patient characteristics, outcomes and definitions included in the literature, and any inconsistencies in recommendations were resolved through consultation. The main data extracted were as follows: the number of medical staff who insisted on wearing masks and those who did not insist on wearing masks.
Literature quality assessment
The quality of the methodology in the included studies was evaluated by using Cochrane Risk of Bias tool[6]. The quality of RCTs was evaluated using RevMan 5.3 software. The risk of bias was evaluated from six perspectives: choice bias, performance bias, measurement bias, attrition bias, reporting bias, other biases (Table 2). According to the criteria for low, unclear and high risk, the quality of the methodology of the included studies was divided into three levels as follows: Mild bias: four or more of the above six items are low risk; moderate bias: two or three of the above six items are low risk; severe bias: none or only one of the above six items is low risk.
Table 2 Cochrane risk of bias assessment form
Evaluation items
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Evaluation content
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Choice bias
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Random sequence generation
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The method of generating random assignment sequence is described in detail, which is convenient for evaluation of the comparability between groups.
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Assignment hidden
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The method of hiding random distribution sequence is described in detail, which is convenient for judging whether the distribution of intervention measures can be predicted.
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Performance bias
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Blind method for researchers and subjects
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The method of blinding used to prevent researchers and subjects from knowing the intervention measures is described in detail. This provides information that can be used to judge whether the blinding method is effective.
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Measurement bias
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Blind evaluation of research results
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The method of blinding used to prevent the evaluators of the research results from knowing the intervention measures is described in detail. This provides information that can be used to judge whether the blinding method is effective.
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Attrition bias
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Integrity of result data
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The data for each major outcome indicator, including those of subjects who were lost or withdrew from the study, are reported completely. Including subjects who were lost or withdrew, the total number of people in each group (compared with the total number of randomly enrolled people), and the reasons for the loss of interview/withdrawal are clearly reported, so as to facilitate assessment of the relevant treatment by the system evaluator.
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Reporting bias
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Selective reporting of research results
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The information described can be used by system evaluators to judge the possibility of selective reporting of research results and relevant information.
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Other biases
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Other sources of bias
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In addition to the above biases, the information provided can be used to assess the existence of other bias factors. If a question or factor is mentioned in the plan, corresponding answers are required.
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Statistical methods
RevMan 5.3 software provided by the Cochrane Collaboration was used to conduct this meta-analysis of the proportions of medical mask use between the experimental and control groups. Q and I2 tests were used to evaluate the heterogeneity of the included studies (Q tests is the traditional method in the heterogeneity test of meta-analysis; I2 tests can measure the degree of difference among multiple research effects, and can describe the percentage of variation caused by inter research in the total variation). When I2 ≤ 50% and P > 0.1, a fixed effect model was used to merge the data; when I2 > 50% or P < 0.1, a random effect model was used to merge the data. The odds ratio (OR) and 95% confidence interval (CI) were used to express the enumeration data. P < 0.05 was considered to indicate statistical significance.