Saturday, August 16, 2014

VDU Blog: Droplets vs Airborne - Demystifying Ebola Transmission


Except from CDC Infographic



# 8962


Almost two weeks ago the CDC released a reassuring infographic (see above) that - among other things - stated that `You can’t get Ebola through Air’, which immediately set off an internet firestorm of disbelief and derision. I considered it a communications misstep at the time, and blogged about it in The Ebola Sound Bite & The Fury.


While I understand the need to reassure the public, and the desire to try to defuse some of more egregious tabloid-style reporting, sometimes reassurance can be overdone.


When people see moon-suited doctors ferrying Ebola patients into Emory University Hospital, and compare that to the CDC’s blanket assurance that `You can’t get Ebola through the Air’  – they rightfully come away confused, and perhaps even a bit suspicious.


Last week, in Ebola: Parsing The CDC’s Low Risk vs High Risk Exposures, we looked at CDC guidance that acknowledged the (low) risks of casual contact; defined as spending a prolonged period of time in the same room with, or within 1 meter, of an infected patient – even without direct physical contact. 


What I dubbed `spittle range’  where large droplets of mucus, blood, sweat, or other bodily fluids could potentially be coughed, sneezed, or otherwise propelled or flung onto another person.  


Today, I’m very pleased to report that Dr. Ian Mackay (along with three other researchers) – all far more qualified to weigh in on this subject than I  – have penned a detailed essay on what we know about Ebola transmission, which will hopefully clear up some of the confusion.  


Follow the link to read:


Ebola virus may be spread by droplets, but not by an airborne route: what that means

An article collaboratively written by (alphabetically)..

Dr. Katherine Arden
A postdoctoral researcher with interests in the detection, culture, characterization and epidemiology of respiratory viruses.

Dr Graham Johnson
A post-doctoral scientist with extensive experience investigating respiratory bioaerosol production and transport during breathing, speech and coughing and determining the physical characteristics of these aerosols.

Dr. Luke Knibbs
A Lecturer in Environmental Health at the University of Queensland. He is interested in airborne pathogen transmission and holds an NHMRC Early Career Fellowship in this area.

A. Prof Ian Mackay
A virologist with interest in everything viral but especially respiratory, gastrointestinal and central nervous system viruses of humans.


The flight of the aerosol

Understanding what we mean when we discuss airborne virus infection risk

A variant Ebola virus belonging to Zaire ebolavirus (EBOV) is active in four West African countries right now. Much is being said and written about it, and much of that revolves around our movie-influenced idea of an easily spread, airborne horror virus. Many people worry about their risks of catching EBOV, particularly since it hopped on a plane to Nigeria. However, all evidence suggests that this variant is not airborne. The most frequent routes to acquire an EBOV infection involve direct contact with the blood, vomit, sweat or stool of a person with advanced Ebola virus disease (EVD). But what is direct contact? What is an “airborne” route? For that matter what is an aerosol and what role do aerosols play in spreading EVD? How is an aerosol different from a droplet spray? Can droplets carry EBOV through the air?

Direct contact includes physical touch but also contact with infectious droplets; the contact is directly from one human to the next, rather than indirectly via an intermediate object or a lingering cloud of infectious particles. You cannot catch EVD by an airborne route, but you may from droplet sprays. Wait, what?? This is where a simple definition becomes really important.

(Continue . . . )


Kathryn said...

How does transmission translate to an enclosed airliner environment, can you comment? Thanks!

Michael Coston said...


Given the lack of real world data, we can only speculate.

But it would seem reasonable that those seated adjacent or very near to a symptomatic Ebola case would be at least at some potential risk of contracting the virus.

The CDC calls that risk `low', particularly when compared to the the risks of direct contact with the patient's body fluids.

As viral shedding increases as the patient grows sicker, that makes it less likely that a really `active spreader' would be capable of boarding a plane.

Based on current knowledge, it doesn't appear that simply being on the same plane - but seated 6 or 10 feet away - would pose much of a risk.

But of course, we'll have a better handle on all of this when more data is collected.