BACKGROUND AND PURPOSE:

• Leung et al. (Nature Medicine, 2020) investigated aerosol routes of transmission to determine the potential efficacy of surgical masks to prevent respiratory virus transmission

METHODS:

• Randomized controlled trial (2013 to 2016)
• Participants
  • Patients with viral symptoms were eligible to participate if they were within 3 days of illness onset and ≥11 years of age
• Interventions
  • Wearing a face mask
  • Not wearing a face mask
• Study design
  • Told to breathe normally | Natural coughing allowed | Conducted for 30 minutes
  • Second sample crossover sample requested (no mask to masked and vice versa) | Most participants did not provide second breath exhalation due to time constraints | 20% (n=49) provided a second sample
  • Nasal and throat swabs collected and analyzed
  • Infections confirmed by reverse transcription PCR (RT–PCR)
    • Human (seasonal) coronavirus (not SARS-CoV-2)
    • Influenza virus
    • Rhinovirus
  • Exhaled breath particles collected and differentiated into 2 size fractions
    • Course fraction (respiratory droplets): Particle aerodynamic diameter >5 μm
    • Fine fraction (aerosols): Particle aerodynamic diatmeter ≤5 μm
• Primary outcome
  • Efficacy of face masks in preventing virus dissemination in exhaled breath
  • Respiratory droplets and aerosols considered separately
• Secondary outcomes
  • Correlation between viral shedding in nose swabs, throat swabs, respiratory droplets and aerosols
  • Factors affecting viral shedding in respiratory droplets and aerosols

RESULTS:

• A total of 246 participants provided breath samples
  • Not wearing a mask: 122
  • Wearing a mask: 124
• Infection with a respiratory virus was confirmed in 123 (50%) of patients, and 111 patients (90%) had at least one of the following
  • Human (seasonal) coronavirus: 17
  • Influenza virus: 43
  • Rhinovirus: 54
• Viral shedding was higher in those with positive nasal swabs than in throat swabs

No Mask Group

• Viral RNA was identified from respiratory droplets and aerosols for all three viruses while not wearing a face mask
  • Human (seasonal) coronavirus
    • Respiratory droplets: 30%
    • Aerosols: 40%
  • Influenza virus
    • Respiratory droplets: 26%
    • Aerosols: 35%
  • Rhinovirus
    • Respiratory droplets: 28%
    • Aerosols: 56%

Mask Group

• Coronavirus
  • There was no coronavirus viral RNA detected in respiratory droplets or aerosols collected from participants wearing face masks
  • Significant reduction by wearing face masks in detection of coronavirus in aerosols (P=0.04)
  • Trend towards reduction in detection in respiratory droplets (P=0.09)
• Influenza
  • Significant reduction in the facemask group in detection of influenza virus in respiratory droplets (P=0.04)
  • No difference was found in aerosols (P=0.36)
• Rhinovirus
  • No significant differences found for either respiratory droplets or aerosols

CONCLUSION:

• Even without masks, majority of patients did not shed virus and those who did, the viral load was relatively low
  • Suggests close contact for longer time frame may be required to transmit these viruses
  • This study evaluated breathing, not coughing
• This study found evidence for aerosol transmission of coronaviruses, influenza, and rhinoviruses
  • If SARS-CoV-2 is similar to other coronaviruses studied here, spread could happen through aerosols
  • The authors suggest that transmission of COVID-19 could be reduced by symptomatic individuals wearing surgical masks

Learn More – Primary Sources:

Respiratory virus shedding in exhaled breath and efficacy of face masks

Related ObG Topics:

Aerosols and Surfaces: SARS-CoV-2 Stability

COVID-19 Guidance: Key Highlights for Healthcare Professionals

CDC Weekly Update: Which Comorbidities are Associated with COVID-19 in the US?