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An article which may point to weaknesses in the presumed safety practices in this New Ebola outbreak.

http://newsoffice.mit.edu/2014/coughs-and-sneezes-float-farther-you-think

Includes high speed video to show effects and longer distance than previously thought possible, thus calling into question the current “safe droplet separation distance” with regard to the spread of pathogens.

With New Ebola presenting flu like symptoms, including coughing and sneezing, it now appears as if virally loaded droplets may pass beyond the rule of thumb 3 foot contact zone for greater projection leaving traces on surrounding surfaces. And those distances are remarkably longer than suspected. In very dense populations such as the West Point quarantined zone, the narrow passages insure constant bumping and brushing against against sweaty neighbors and confining surfaces.

Skins swabs of non PPE wearing HCWs might be in order to test for the presence of EV.

The MIT study might also apply to the hand spraying of bleach solutions. Turbulence from the spray may lift deposited droplets into the ambient air before bleach solution makes contact. Total immersion into the bleach solution might make better sense.

As with any battlefield medicine, field expediant techniques may outpace laboratory testing without full understanding of why they work.

(Excerpt)

he paper, “Violent expiratory events: on coughing and sneezing,” was published in the Journal of Fluid Mechanics. It is co-written by Bourouiba, Bush, and Eline Dehandschoewercker, a graduate student at ESPCI ParisTech, a French technical university, who previously was a visiting summer student at MIT, supported by the MIT-France program.

Smaller drops, longer distances
The researchers used high-speed imaging of coughs and sneezes, as well as laboratory simulations and mathematical modeling, to produce a new analysis of coughs and sneezes from a fluid-mechanics perspective. Their conclusions upend some prior thinking on the subject. For instance: Researchers had previously assumed that larger mucus droplets fly farther than smaller ones, because they have more momentum, classically defined as mass times velocity.
That would be true if the trajectory of each droplet were unconnected to those around it.

But close observations show this is not the case; the interactions of the droplets with the gas cloud make all the difference in their trajectories. Indeed, the cough or sneeze resembles, say, a puff emerging from a smokestack.

“If you ignored the presence of the gas cloud, your first guess would be that larger drops go farther than the smaller ones, and travel at most a couple of meters,” Bush says. “But by elucidating the dynamics of the gas cloud, we have shown that there’s a circulation within the cloud — the smaller drops can be swept around and resuspended by the eddies within a cloud, and so settle more slowly.

Basically, small drops can be carried a great distance by this gas cloud while the larger drops fall out. So you have a reversal in the dependence of range on size.”

Specifically, the study finds that droplets 100 micrometers — or millionths of a meter — in diameter travel five times farther than previously estimated, while droplets 10 micrometers in diameter travel 200 times farther.

Droplets less than 50 micrometers in size can frequently remain airborne long enough to reach ceiling ventilation units.

A cough or sneeze is a “multiphase turbulent buoyant cloud,” as the researchers term it in the paper, because the cloud mixes with surrounding air before its payload of liquid droplets falls out, evaporates into solid residues, or both.

“The cloud entrains ambient air into it and continues to grow and mix,” Bourouiba says. “But as the cloud grows, it slows down, and so is less able to suspend the droplets within it. You thus cannot model this as isolated droplets moving ballistically.”

(Cut)

Lidia Morawska, a professor at Queensland University of Technology in Brisbane, Australia, who has read the study, calls it “potentially a very important paper” that suggests people “might have to rethink how we define the airborne respiratory aerosol size range.”

However, Morawska also notes that she would still like to see follow-up studies on the topic.

The MIT researchers are now developing additional tools and studies to extend our knowledge of the subject. For instance, given air conditions in any setting, researchers can better estimate the reach of a given expelled pathogen.

“An important feature to characterize is the pathogen footprint,” Bush says. “Where does the pathogen actually go?

The answer has changed dramatically as a result of our revised physical picture.”
Bourouiba’s continuing research focuses on the fluid dynamics of fragmentation, or fluid breakup, which governs the formation of the pathogen-bearing droplets responsible for indoor transmission of respiratory and other infectious diseases. Her aim is to better understand the mechanisms underlying the epidemic patterns that occur in populations.

“We’re trying to rationalize the droplet size distribution resulting from the fluid breakup in the respiratory tract and exit of the mouth,” she says. “That requires zooming in close to see precisely how these droplets are formed and ejected.”

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Question for the thread.

Has anyone come across a full Level-4 autopsy report and lab results from such? Hard to imagine that previously occurring in Africa. New Ebola is proving we know far less about the Ebola strains than we think.

“With New Ebola presenting flu like symptoms, including coughing and sneezing”

Frankly speaking, I have not come across any mention of a “New Ebola” or references to sneezing.

While I have seen indications in the early onset of Ebola Zaire where a minority of patients complained of a sore throat, I would think that coughing would be incidental at best due to nasal secretions..but Ebola in human form is not known to infect the lungs.

There is no current safe distance that I am aware of as it applies to distance from patients while in line of sight.. Ebola in all it’s forms can be transmitted via aerosols. The distance they travel would be a factor of droplet size and the force that ejects them. They can also land on surfaces and be picked up there.

Anyone entering a room with end stage or mid stage Ebola patients would be remiss not to use a mask, gown, eye protection and also to have the patient masked. prior to that, and until the virus load overwhelms the host, they don’t general shed through aerosols to my knowledge. But one would take precautions in any case.

The same sort of precautions should be used with hospitalized cases on influenza or any virus that can be transmitted in that way.