Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis

Abstract

This systematic review and meta-analysis quantified the protective effect of facemasks and respirators against respiratory infections among healthcare workers. Relevant articles were retrieved from Pubmed, EMBASE, and Web of Science. Meta-analyses were conducted to calculate pooled estimates. Meta-analysis of randomized controlled trials (RCTs) indicated a protective effect of masks and respirators against clinical respiratory illness (CRI) (risk ratio [RR] = 0.59; 95% confidence interval [CI]:0.46-0.77) and influenza-like illness (ILI) (RR = 0.34; 95% CI:0.14-0.82). Compared to masks, N95 respirators conferred superior protection against CRI (RR = 0.47; 95% CI: 0.36-0.62) and laboratory-confirmed bacterial (RR = 0.46; 95% CI: 0.34-0.62), but not viral infections or ILI. Meta-analysis of observational studies provided evidence of a protective effect of masks (OR = 0.13; 95% CI: 0.03-0.62) and respirators (OR = 0.12; 95% CI: 0.06-0.26) against severe acute respiratory syndrome (SARS). This systematic review and meta-analysis supports the use of respiratory protection. However, the existing evidence is sparse and findings are inconsistent within and across studies. Multicentre RCTs with standardized protocols conducted outside epidemic periods would help to clarify the circumstances under which the use of masks or respirators is most warranted.

Keywords: Facemasks; N95 respirators; influenza; respiratory infections; severe acute respiratory syndrome (SARS).

Figure 1.

Summary of the literature search and inclusion process.

Figure 2.

Meta-analysis of RCTs assessing the protective effect of medical masks and N95 respirators against clinical and laboratory-confirmed respiratory outcomes. Meta-analyses comparing the risk of (A) clinical respiratory illness (CRI), (B) influenza-like illness (ILI) or (C) laboratory-confirmed viral respiratory infection (VRI) among HCWs continuously wearing respiratory personal protective equipment (rPPE) during working hours and convenience-selected HCWs wearing no mask (MacIntyre 2011 [42]) or following routine care, which may or may not include mask wearing (MacIntyre 2015 [41]). (A) CRI = 2 or more respiratory symptoms, or one respiratory symptom and a systemic symptom; (B) ILI = fever ≥38°C and 1 respiratory symptom; (C) VRI = detection of adenovirus, metapneumovirus, coronavirus 229E ⁄ NL63, parainfluenza 1- 3, influenza A and B, respiratory syncytial virus A and B, rhinovirus A⁄ B or coronavirus OC43⁄HKU1 by multiplex PCR. Abbreviations: CI, confidence interval; HCW, healthcare worker; med, medical mask; n/N, number of cases/number at risk; PCR, polymerase chain reaction; RCT, randomized controlled trial; RR, risk ratio.

Figure 3.

Meta-analysis of RCTs comparing the protective effect of N95 respirators and medical masks against clinical respiratory outcomes. Protective effect of N95 respirators compared to medical masks against (A) clinical respiratory illness (CRI) or (B) influenza-like illness (ILI). Masks and respirators were worn at all times during the work shift (MacIntyre 2011 [42] and MacIntyre 2013 [44]) or only when providing care to patients with febrile respiratory illness (Loeb 2009 [45]). (A) CRI = 2 or more respiratory symptoms, or 1 respiratory symptom and a systemic symptom; (B) ILI (MacIntyre 2011 [42] and MacIntyre 2013 [44]) = fever ≥38°C and 1 respiratory symptom; ILI (Loeb 2009 [45]) = fever ≥38°C and cough. Abbreviation: CI, confidence interval; n/N, number of cases/number at risk; RCT, randomized controlled trial; RR, risk ratio.

Figure 4.

Meta-analysis of RCTs comparing the protective effect of N95 respirators and medical masks against laboratory-confirmed respiratory outcomes. Protective effect of N95 respirators compared to medical masks against laboratory-confirmed (A) bacterial respiratory infection (BRI), (B) influenza or (C) other viral respiratory infections (VRI). Masks and respirators were worn at all times on shift (MacIntyre 2011 [42], MacIntyre 2013 [44] and MacIntyre 2014 [43]) or only when providing care to patients with febrile respiratory illness (Loeb 2009 [45]). (A) BRI = detection of Streptococcus pneumoniae, Legionella, Bordetella pertussis, Chlamydia, Mycoplasma pneumoniae, or Haemophilus influenzae type B by multiplex PCR. (B) Influenza = laboratory-confirmed influenza A or B in symptomatic subjects. (C) VRI (MacIntyre 2011 [42], MacIntyre 2013 [44]) = detection of adenovirus, metapneumovirus, coronavirus 229E ⁄ NL63, parainfluenza 1–3, influenza viruses A and B, respiratory syncytial virus A and B, rhinovirus A/ B or coronavirus OC43 ⁄HKU1 by multiple PCR; VRI (Loeb 2009 [45]) = detection of respiratory syncytial virus A and B, metapneumovirus, parainfluenza 1–4, rhinovirus, coronavirus OC43, 229E, NL63, and HKU1by multiplex PCR. Abbreviations: CI, confidence interval; n/N = number of cases/number at risk; PCR, polymerase chain reaction; RCT, randomized controlled trial; RR, risk ratio.

Figure 5.

Meta-analysis of observational studies assessing the protective effect of masks and respirators against SARS infection. (A)–(C) Five case-control (empty squares) and 3 cohort (full squares) studies were combined into different meta-analyses to assess the protective effect of (A) any respiratory personal protective equipment (rPPE), including medical masks, paper masks, disposable masks, and N95 respirators, (B) medical masks or (C) N95 respirators. Controls for studies included in meta-analyses (A)–(C) were HCWs not wearing any rPPE, except for Loeb 2004 [20] and Lau 2004 [36], where the control group consisted HCWs reporting “inconsistent use” of masks or respirators; med = medical mask; pap = paper mask; dis = disposable mask; n/N = number of cases/number at risk. ^aHCWs wearing N95 during non-invasive positive-pressure ventilation. ^bOutcome = incidence of pneumonic SARS (excludes asymptomatic SARS cases). (D) Meta-analyses combining observational studies comparing the protective effect of N95 and medical masks against SARS. NOS scores = Newcastle-Ottawa-Scale scores; for each paper, light gray, mid-gray, and dark gray circles represent the score for the “Selection,” “Comparability” and “Exposure” (case-control studies) or “Outcome” (cohort studies) domains of the Newcastle-Ottawa score, respectively. For each meta-analysis (A–D), panels on the right-hand side display a range of plausible risk ratios corresponding to the summary effect estimate for an estimated baseline risk of SARS ranging from 20% to 60%. Abbreviations: CI, confidence interval; HCW, healthcare worker; med, medical mask; n/N, number of cases/number at risk; RR, risk ratio; SARS, severe acute respiratory syndrome.