The physics of sneezes is at the heart of understanding
how pathogens of one individual
become the pathogens of another.
So without that step of transportation of the pathogens
from one host to the other, there is no epidemic;
there is no disease transmission.
And it turned out that we don’t actually understand
much about that physics.
So the work that we do
is combining fluid mechanics
with problems that are relevant in health and epidemiology
to understand better how pathogens are transmitted.
I started being interested in sneezes
when I finished a piece of work on influenza transmission
and while doing that work, what we realised is that
the parameter choices to describe the contamination process
from one host to another are very limited.
The processes themselves are not really well known.
So if you’re the head of a hospital,
for example like MGH, and trying to figure out
– okay, we have, right now, an epidemic that is ongoing
– what kind of measures should I ask my staff to take?
They are guessing right now.
You are in the lab right now which is a BL2 lab:
Biosafety Level 2.
So I’ll take you all around.
We’re in the middle of a move so it’s a little cluttered.
This is basically the microbiology corner.
Here in this area, there’s a lot of work
that entails looking at fragmentation and
break up
from a more fundamental level.
And these are the type of cameras that we used
for characterising violent expirations: coughs, sneezes.
This particular one is basically a camera
that allows us to go to about a million frames per second.
And the reason why we need this very high frame rate
is because these events happen very quickly.
We tried all sorts of approaches to try to trigger the sneezes.
Some included light-sensitivity, pepper, various additives
but I really wanted to achieve a natural sneeze and so ultimately,
the method that ended up being reproducible at all times
was nose tickling.
And so, nose tickling is the universal method.
Sneezes are actually really interesting.
They’re multi-phase, turbulent clouds
so there are all sorts of scales also involved.
But at the same time it’s a complex flow
because you have a gaseous faze that is coupled with droplets,
and eventually the final residue of these drops,
which could be solid residues containing the pathogens.
And so there are a lot of interesting, open problems
of physics and fluid dynamics embedded in it.
At this point we understand much better
how sneezes and coughs actually function.
The overall dynamics of contamination
– so the second part of the story outwards from the patient
– is, right now, something that we understand quite well.
The only aspect that we are still working on
is to refine the question of
how is that affecting the actual fate of the pathogens, ultimately?
From the other side of the story
which is going backwards in the host,
there are still a lot of open questions.
But we are planning to look at them
once we get to phase two of
the work
– bringing in human subjects that are infected and healthy
– because we will then start to look at the differences
in the physiology and the lung capacity in health and infection
and how all of that can modulate what we already saw
in terms of emissions outside of the mouth.
