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Grand Rounds

The Evidence Behind Physical Distancing and Face Masks to Reduce Viral Transmission

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BACKGROUND AND PURPOSE:

  • Chu et al. (Lancet, 2020) investigated the effects of physical distance, face masks, and eye protection on SARS-CoV-2 and other virus transmission in both healthcare and non-healthcare settings

METHODS:

  • Systematic review and meta-analysis
  • Data sources
    • 21 standard WHO-specific and COVID-19-specific sources from database inception to May 3, 2020
  • Inclusion criteria
    • Comparative studies and data on
      • Acceptability | Feasibility | Resource use | Equity
  • Study design
    • Data were obtained for
      • SARS-CoV-2
      • Betacoronaviruses
      • MERS
    • Authors screened records, extracted data | Data duplication bias also assessed
    • Certainty of evidence was rated according to Cochrane methods and the GRADE criteria
  • Primary outcomes
    • Optimum distance for avoiding person-to-person virus transmission
    • Virus transmission with use of face masks and eye protection

RESULTS:

  • 172 observational studies | 44 comparative studies | 25,697 patients | Across 16 countries
  • Transmission of viruses was lower with physical distancing of ≥1 meter (3.28 feet) vs <1 meter
    • Pooled adjusted odds ratio (aOR) 0.18 (95% CI, 0.09 to 0.38)
    • Risk difference (RD) −10.2% (95% CI, −11.5 to −7.5)
  • Protection against transmission increased as distance increased
    • Change in relative risk (RR) 2.02 per meter
  • Face mask use could result in a large reduction in risk of transmission
    • aOR 0.15 (95% CI, 0.07 to 0.34)
    • RD −14.3% (95% CI, −15.9 to −10.7)
  • For exposed individuals, N95 or similar respirators or face masks (eg, disposable surgical masks) were associated with reduced infection risk
    • Adjusted aOR 0.15 (95% CI, 0.07 to 0.34)
    • Association strongest in healthcare setting
      • Health-care settings: RR 0.30 (95% CI, 0.22 to 0.41)
      • Non-healthcare settings: RR 0.56 (95% CI, 0.40 to 0.79)
  • Reduced transmission risk was more strongly associated with N95 of similar respirators vs disposable surgical masks
    • N95 or similar respirators: aOR 0.04 (95% CI, 0.004 to 0.30)
    • Other masks: aOR 0.33 (95% CI, 0.17 to 0.61)
  • Use of eye protection was also associated with reduced infection
    • aOR 0.22 (95% CI, 0.12 to 0.39)
    • RD −10.6% (95% CI, −12.5 to −7.7)
  • Unadjusted studies and subgroup and sensitivity analyses showed similar findings

CONCLUSION:

  • This systematic review and meta-analysis found support for maintaining physical distance of at least 1 meter to reduce viral transmission
  • Use of face masks and eye protection were also associated with reduced infection
  • Authors recognize that lack of RCTs is an important study limitation, however, based on the best available evidence

Current policies of at least 1 m physical distancing are associated with a large reduction in infection, and distances of 2 m might be more effective

These data also suggest that wearing face masks protects people (both health-care workers and the general public) against infection by these coronaviruses, and that eye protection could confer additional benefit

Learn More – Primary Sources:

Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

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Related ObG Topics:

Surgical Masks Reduce Viral Shedding
Aerosols and Surfaces: SARS-CoV-2 Stability
COVID-19 Guidance: Key Highlights for Healthcare Professionals

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