The trajectories of aerosols in the three events:

Aerosol vs Droplet Transmission via Sneezing, Coughing, Exhaling

•   Direct spray of large droplets onto conjunctiva/other mucous
     membranes via talking, coughing, sneezing, etc.  
•  Touching fomites (infected surfaces of inanimate objects)


University of South Florida

Determining this has critical implications: 

If primarily spread via droplets, then masks, distancing rule (6ft), etc. are effective in preventing transmission. Conversely, if primarily spread via aerosols, then preventative measures become less effective and thus need to be modified. 

Examining the source of transmission for both types of respiratory particles are crucial.



Aerosol versus Droplet Debate

Jayaweera, M., Perera, H., Gunawardana, B., & Manatunge, J. (2020). Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy. Environmental Research, 188, 109819. Advance online publication.

doi: 10.1016/j.envres.2020.109819

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293495/

Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy

- Medical procedures

- Fast-running tap water and toilet flushes

- Sneezing, coughing, exhaling

- Droplet nuclei suspended in air due to evaporation of droplets


Sources of Transmission by Aerosols

Sources of Transmission by Droplets 

- temperature

- humidity

- radiation

- open/closed space

- safeguard present or absent


Factors Affecting Aerosol and Droplet Dispersion

Studying the generation and mobility of droplets and aerosols are of the utmost importance in order to develop adequate safeguards. The improvement of these safeguards is crucial, especially for healthcare workers who are exposed to viral particles via patients infected with COVID-19. 


Safeguards Against Transmission of Aerosols and Droplets 

This article argues that if COVID-19 relied on primarily airborne transmission, then its reproductive number (R0) should be considerably higher. 

A comparison to another respiratory virus that relies mainly on airborne transmission, the measles, shows that COVID's R0 value is much less than the measles, which had a value of 18. This might be partially due to the efficacy of existing safeguards.


Theoretical Consideration of COVID-19's Reproductive Number

The COVID-19 pandemic results in unprecedented containment and mitigation policies intended to slow the transmission of SARS-CoV-2. While these measures have been proven to be effective, the host-to-host transmission models for respiratory infectious diseases are predicated on a transmission model that doesn’t reflect transmission complexity. This study evaluates the understanding of turbulent gas clouds that can carry clusters of droplets and stay in the air longer than isolated droplets.

Turbulent Gas Clouds and Respiratory Pathogen Emissions

The authors of this study assessed the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces.

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1

A study examining the evidence for Covid-19 transmission through aerosol concluded that the claim is supported through three reasonings:
- Cases of asymptomatic patients transmitting the virus to other people
- Some studies have recorded aerosolized SARS‐CoV‐2 particles that have stayed in the air for an extended period.
- Other viruses similar to Covid-19 have been recorded with aerosol transmission





Consideration of the Aerosol Transmission for COVID‐19 and Public Health

To understand the aerosol transmission route of SARS-CoV-2, this study aimed to:
-	Quantify the concentrations of airborne SARS-CoV-2 both inside hospitals and in outdoor areas where public gatherings are common
-	Evaluate the aerodynamic size distributions of SARS-CoV-2 aerosols that may facilitate its airborne transmission in different settings
-	Determine the dry deposition rate of the airborne SARS-CoV-2 in an ICU patient ward room

It concluded that:
- Room ventilation, open space, and proper disinfection of toilets can limit aerosol transmission of virus particles
- Crowds with asymptomatic carriers is a potential source of airborne SARS-CoV-2
- The virus aerosol deposition on PPE or floor surfaces and subsequent resuspension is a potential transmission pathway
- Rigorous sanitization protocols are critical in slowing the spread of the virions

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