Aerosolization Vs Airborne

What is the difference between Airborne and Aerosolization when talking about Ebola?

With the recent Ebola events, new talk of the virus being airborne is all over the news .  I wanted to take a moment and talk about airborne or aerosolized pathogens.  Aerosolization is when a particle is small enough and light enough that the particle is suspended in and carried by the air currents.  Aerosolization can be naturally occurring or man made.  

A particle or droplet larger than 10 micrometers or 10μm can be transmitted over a short distance of around  2 - 4 meters this would be called -Droplet transmission. 

A particle or droplet smaller than 10μm can be transmitted over longer distance - hundreds of feet depending on environmental conditions, this is called - Airborne transmission.

Keep in mind the sizes above when we talk about transmitting the particle over short distances Vs long distances coming up.

Some common  actions which cause Aerosolization of particles include 

• Sneezing
  
• Coughing
• Exhaling 
• Vomiting
• Speaking
• Urinating (stream splattering against hard surface)
• Hand washing
• Flushing of toilet
• Brushing teeth

Since we spoke specifically about Ebola, lets quickly state some of the size characteristics of the Ebola virus.
Ebola virus is approximately 970 nano meters (nm) long and 80nm in diameter.  

I searched and found limited information on the mass of the Ebola virus.  This will be important for our next point.  What I did find established that the mass of a specific Ebola virus being studied was approximately 50 to 60nm in overall size.  That would be approximately 16μm or 16 micrometers.  

1 micrometer or ( 1 μm ) = 1 000 nanometers  or ( 1 000 nm) -reference

You are probably asking why this matter.  The size of the virus matters when we are looking at determining what the particle will do when Aerosolized.  It will also help us better speak using terminology which reflects the current data on the Ebola virus.

The CDC has studied Aerosolization and how particles of differing sizes act in still air and in turbulent air.  This is why we need to have a general idea of the overall size of the Ebola virus, by knowing how big it is we can then compare that size to the CDC particle behavior charts.

We are using the proposed overall Ebola size of 16μm for our particle behavior comparison. 

The First chart will depict a particle settling in still air.  Our 16μm particle would have an approximate time to settle of 6 minutes in still air.

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The next chart depicts a particle settling in turbulent air.  The same 16μm particle would have an approximate time to settle of 6 minutes in turbulent air.

Below the chart shows particles settling in a closed room with still and turbulent air depicted. 

We see from comparing our proposed 16μm Ebolla virus to the CDC charts above that the approximate settle time for a particle this size in both still and turbulent air would be around 6 minutes.  6 minutes of floating around, not taking into consideration HVAC spreading the particle further than it would have naturally achieved. 

Our proposed Ebolla particle of 16μm would fall in the "over 10μm" particle size and therefore be considered to have a short effective transmission distance of 2 - 4 meters with an airborne time of approximately 6 minutes. Using the term "Airborne" when speaking about Ebolla in my opinion is correct.  when adding in "Airborne" it should also be noted to what extent the particle or virus is "Airborne".  One might want to cage their classification of "Airborne" with the "short transmission distance" and "time to settle (hang time)" of the virus in the air.

Viability of virus outside host
How long will the virus stay infectious outside a living host?  The time can vary greatly from a few minutes up to 51 days in one case study -reference.  The reason there is so much variation in the viability of the virus is due to environmental considerations.  

Main take away
Stay away from people with Ebola!