What’s the role of small droplets or aerosolized particles in the transmission of Covid-19?

Although transmission of SARS-CoV-2 is often considered to occur through large respiratory droplets by coughing or sneezing, emerging data suggests that smaller respiratory particles (5 microns or less) generated by breathing, speaking or singing also account for a sizeable number of infections. Several lines of evidence make a cogent argument for aerosols serving as an important mode of transmission for SARS-CoV-2. 1-9

 First, there are ample accounts of SARS-CoV-2 spreading by being near an infected individual without symptoms.  Since by definition, those without symptoms do not cough or sneeze transmission must have occurred through other means, including breathing, talking or touching surfaces that might have become secondarily contaminated through aerosol.1,2,5  To make matters worse, the peak of contagion in infected individuals occurs on or before symptoms occur.1

Second, aerosolized SARS-CoV-2 has been shown to remain viable in the air for at least 3 hours and viral RNA (not necessarily viable virus) has been found in the air outside patient rooms and inside patient rooms in the absence of cough.2,9 One study found SARS-CoV-2 in outdoor air at a hospital entrance and in front of a department store.7

Third, contaminated air samples and long-range aerosol transport and transmission have been reported by several studies involving a related coronavirus, SARS-CoV-1, the agent of SARS.2

What’s the ramifications of aerosol transmission of Covid-19? The most obvious is the requirement for universal wearing of masks or face covers in public spaces even when 6 feet apart. This practice is particularly important indoors where the amount of ventilation, number of people, duration of stay in the facility, and airflow direction may impact the risk of exposure to SARS-CoV-2.1

The other potential ramification of aerosolized SARS-CoV-2 is that due to their smaller size, these virus-laden particles may bypass the upper respiratory tract and be inhaled directly into the lungs resulting in more severe disease.4  So it really makes sense to routinely wear a mask when out in public places.

Bonus Pearl: Did you know that 1 minute of loud speaking could generate over 1000 virus-containing aerosols in the air with a “super-emitter” generating over 100,000 virus particles in their droplets during the same time?1

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 References

  1. Prather KA, Wang CC, Schooley RT. Reducing transmission of SARS-CoV-2. Science. May 27, 2020.
  2. Anderson EL, Turnham P, Griffin JR, et al. Consideration of the aerosol transmission for COVID-19 and public health. Risk Analysis 2020;40:902-7.
  3. Hamner L, Dubbel P, Capron I, et al. High SARS-CoV-2 attack rate following exposure at a choir practice-Skagit County, Washington, March 2020. MMWR 2020; 69: 606-10.
  4. Gralton J, Tovey E, McLaws ML, et al. The role of particle size in aerosolized pathogen transmission: a review. J Infect 2011;62:1-13.
  5. Asadi S, Bouvier N, Wexler AS et al. The coronavirus pandemic and aerosols: does COVID-19 transmit via expiratory particles. Aerosol Sci Technol 2020;54:635-38.
  6. Morawska L, Cao J. Airborne transmission of SARS-CoV-2: the world should face the reality. Env International 2020;139:105730.
  7. Liu Y, Ning Z, Chen Y, e al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature 2020;582:557-60. https://www.nature.com/articles/s41586-020-2271-3.pdf
  8. Somsen GA, van Rijn C, Kooij S, et al. Small droplet aerosols in poorly ventilated spaces and SARS-CoV-2 transmission. Lancet Respir Med 2020; May 27. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7255254/pdf/main.pdf

9. Santarpia JL, Rivera DN, Herrera V, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center. 2020 (Preprint) https://www.ehs.ucsb.edu/files/docs/bs/Transmission_potential_of_SARS-CoV-2.pdf

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What’s the role of small droplets or aerosolized particles in the transmission of Covid-19?

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