The power of a sneeze

Bacteria and viruses hitch a ride inside droplets of all kinds—sneezes, raindrops, toilet splatter. By reviewing footage of different types of drops, an applied mathematician records and measures where they disperse in order to better understand how diseases spread.


Bacteria and viruses hitch a ride inside droplets of all kinds -- sneezes, raindrops, toilet splatter.

By reviewing footage of different types of drops, an applied mathematician records and measures where they disperse in order to better understand how diseases spread.

Our partner, 'Science Friday,' has the story.

When I'm in nature, I see mathematics.

The sun, the sky being blue.

I see the clouds forming that contain all these droplets.

Everybody's trying to capture the essence of what governs the world around us, and the best way to capture that, instead of having words, is an equation.

An equation, a mathematical equation, is truly the universal language that transcends fields, transcends ideas, but also transcends cultures and countries.

Bacteria, viruses, spores are transported in droplets.

Knowing basically where it goes is the crux of this whole problem to understand better how diseases spread.

If you look at disease transmission, it's based on humans reporting, and so the data is not the best data.

But, in fact, the best way to say anything is to measure it directly.

My name is Lydia Bouroubia, and I'm a professor at MIT, Massachusetts Institute of Technology, and I do research in fundamental fluid dynamics to answer questions in disease transmission.

We're trying to understand very fundamental neglected questions that are important to control the spread of disease, but yet approaching them in a unique way through mathematics.

Growing up in Algeria, we would go camping.

Beaches there are quite wild.

I would watch the waves breaking for hours and look actually at the trails of the sand.

Why is it doing this sound and why do we have these patterns?

Growing up, what I realized was that mathematics and science was really truly universal, and that if you go into this direction early on, then you could really go anywhere after.

At the PhD level, I wanted to find a way that I could give back and leverage all this knowledge and all this education to help the world.

My grandmother died of tuberculosis, and some other members of the family died of tuberculosis, which is also transported in droplets.

And it just hit me that epidemiology and infectious diseases was an area that really I felt very strongly about.

We've sent people to the moon, but then we have people that don't have clear water to drink and are infected by diseases that should be eradicated by now.

Droplets are really at the heart of this whole problem of transmission.

Sneezes, coughs, respiratory events are probably the place, the physical aspect that we should be looking at.

To record a sneeze -- so sneeze, cough, or any of these violent expiration events -- there's a few key things that need to be put in place.

The lighting, the intensity, the orientation, the angles.

At the beginning, it's a bit awkward.

For sneezing, we tried, you know, light sensitivity, dust, pepper, but it turns out that tickling the nose was the most universal way of getting the human subjects to sneeze.

When you zoom in and you look at various parts of the clouds, look like snowflakes, and it's really beautiful.

Taking an image that you can analyze precisely to extract clean enough data at high enough precision is very difficult, and image analysis becomes a critical tool.

Now we can actually extract features very precisely in terms of droplet sizes, speeds, but also what actually is happening to the whole fluid.

The research showed the droplets are heavy and are gonna fall very quickly, but most of them, in fact, are trapped, and they're swirling around moving.

You have this moment that dominates the earlier stage, but then this cloud has buoyancy because it is hot and moist.

So if you think about hot air, it's buoyant, meaning that it's basically lighter in comparison to cold air, and therefore it's gonna go up.

A lighter fluid goes up and a heavier fluid goes down.

And eventually, when the cloud slowed down sufficiently, you see the cloud with some angle moving upward.

That's very important because most modern rooms' ventilation systems are upward, so where the cloud is sucked out to be re-circulated.

This problem of transmission, we find it also between plants.

There was correlation between rainfalls and when the spots of infection appear in the leaves a few weeks later.

You have rainfalls or irrigation on contaminated plants through the droplets that are created.

Nobody actually put a camera there to actually see what happens.

We basically constructed a very detailed drop tower where we had the leaf being the centerpiece and then have basically drops falling on it.

We thought we would see bouncing.

We never saw that.

We see the contaminated drop relying completely on the motion of the leaf itself to create droplets of different signatures, of sizes and distances.

Therefore, the overall range of contamination around this species is this and around that species is this.

I wanted to understand if there was a true potential for droplet creation in hospitals.

There are all sorts of diseases that you could get from a hospital like Clostridium Difficile.

A lot more people now are dying from it.

Instead of the sneezers, we just had this basically toilet flush.

It was kind of an awkward setup.

We use high-pressure toilet that was used in hospitals and also high-speed cameras for this problem.

One flush.

[ Toilet flushes ] There's studies that reported that sprays are coming out from flushing, but during visualization of this to quantify exactly where it's coming from, what type of droplet size distribution, how far these things are going, it's quite shocking.

When you think of the impact potentially for contamination and transmission, it's quite disturbing.

But there's a lot of simple questions to be asked about is this design of the hospitals optimized to minimize basic transmission between patients?

Now we can actually start revisiting our ventilation systems and also the way that wards are designed in times of emergency when you have to put something together very quickly because you are the front line.

Ultimately, pathogens are transported in droplets.

All the work that we're doing in the lab relates one way or another to how the drops are created, whether it's from sneezing or splashes on plants or et cetera, et cetera.

When I'm in nature, I see fluid dynamics and mathematics all the time.

Science and mathematics and physics crosses all the boundaries.

You find it to describe any laws of nature, and we find it also in other fields like sociology, economics.

We can start seeing that all humans are connected not only through universal feelings, but through very rational ways of understanding the world around us because mathematics is everywhere.