Respiratory virus shedding in exhaled breath and efficacy of surgical face masks

Apr 27, 2020COVID Literature Appraisal, Prevention: Non drug strategies

The article reports the protective efficacy of wearing of surgical facemasks by patients with ARI against transmission of coronaviruses and influenza viruses in exhaled respiratory aerosols and droplets. The findings reported with reference to coronavirus are based on data constrained by poor sample size and not collected during the current pandemic of SARS-CoV-2


  • Randomised design for the intervention. Paucity of literature in the domain. Exhaled breath particles were separated as larger (>5 μm) droplets and smaller (<5 μm) aerosols.


  • Very small sample size (n=11 and n=10, for the intervention and and control arms respectively for the data on Corona virus)
  • The reported data on protective efficacy of surgical masks which could effectively reduce virus transmission in aerosols but not in larger respiratory droplets containing corona virus seems incongruous and defies logic.
  • Limited sampling time of only 30 min for collection of exhaled breath samples, forced coughing was not not encouraged for better yield
  • Data was collected during 2013-16 and does not apply to current SARS-CoV-2


Article: Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med (2020).  Link


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