COVID-19: small study raises questions about the value of surgical and cotton masks

  • Bae S & al.
  • Ann Intern Med
  • 6 Apr 2020

  • curated by Liz Scherer
  • Clinical Essentials
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Takeaway

  • Surgical and cotton masks may be of questionable utility in preventing SARS-CoV-2 air droplet dissemination from coughs of patients with COVID-19, according to findings in this small study.

Why this matters

  • WHO continues to state that evidence supporting community use of face masks is limited, particularly for healthy individuals living or in contact with persons who have tested positive for SARS-CoV-2.
  • Patients should follow national guidance, including proper wearing, removal, and disposal of masks, as well as related proper hand hygiene after touching outer mask surfaces.

Study design

  • 4 patients were instructed to cough 5 times under each mask condition onto a Petri dish containing 1 mL viral transport media.
  • Test sequence: no mask, surgical mask, cotton mask, no mask. 
  • Swab sequence: outer and inner swabs for each mask type.
  • Funding: Fund Project for Infectious Disease Research, Republic of Korea.

Key results

  • Median sample viral loads (log copies/mL):
    • Nasopharyngeal: 5.66.
    • Saliva: 4.00.
  • Median Petri dish viral loads (log copies/mL) after a cough:
    • No mask: 2.56.
    • Surgical mask: 2.42.
    • Cotton mask: 1.85.
  • In 3 of 4 tests of the surgical and cotton masks, the inner surfaces of the masks were negative.
  • Outer mask surfaces were positive after all tests, with ranges of 2.11-2.63 log copies/mL for the surgical masks and 2.58-3.61 log copies/mL for the cotton masks.

Limitations 

  • Only 4 patients included.
  • N-95 masks not tested.
  • Transmission dynamics not reflected.