How Far Do Germs Travel?

  • By Anna Rothschild
  • Posted 11.19.15
  • NOVA

How far do coughs, sneezes, and vomit travel? Way farther than you might think. Find out how scientists track the germs that fly out of our faces in this episode of Gross Science

Running Time: 02:44


How Far Do Germs Travel?

Posted: November 19, 2015

How far do coughs, sneezes, and vomit travel? Way farther than you might think.

I’m Anna Rothschild, and this is Gross Science.

For decades, researchers have wondered exactly what happens to the liquids that fly out of our noses and mouths when we’re sick. But how do you track a tiny particle of phlegm or barf and the microbes they carry?

Well, back in the 1930s, Harvard scientist William Firth Wells gave it a shot. Wells used “sneeze powder” to make whole rooms full of people sneeze at once. Then he sampled the air and found it full of bacteria, though less so if he let his subjects use handkerchiefs.

These days, scientists can use high-speed cameras to see the juicy details of sneezes and coughs. That’s what researchers at MIT did in 2014. They found that the droplets in a cough or sneeze travel on an invisible gas cloud, which can carry germs much farther than people previously thought. Small droplets can fly all the way across a room, and can get sucked into ceiling air vents, which could spread them even further.

And that’s not all. To study what happens when someone’s really sick, scientists in the United Kingdom built a robot called Vomiting Larry, who’s basically just a head and stomach. The researchers were studying norovirus, which is a nasty bug that causes nausea, diarrhea, and projectile vomiting. To simulate the act of puking, they filled Larry’s gut with fluorescently dyed water. Then they made him retch it up.

The dye showed that Larry’s puke particles scattered farther than they would have been able to see with the naked eye. One projectile vomiting episode could actually contaminate close to eighty four square feet. That means viruses might linger in places we think are clean. And in the case of norovirus, those germs might stay active for days or weeks outside of a host.

Recently, in a study with a different vomiting machine—and, yes, there’s more than one—researchers at North Carolina State University found that some viral particles can be suspended in air after puking, as well. The numbers were pretty small, but in the case of norovirus, which these scientists were modeling, as few as twenty particles can cause infection. And when those viruses get into their next victim, they start the cycle of splatter all over again.




Host, Producer, Editor, Animator, Additional Research
Anna Rothschild
Researcher, Writer
Elizabeth Preston
DP, Sound, Additional Research
Ceri Riley
Ragtime Piano
Music Provided by APM


Original Footage
©WGBH Educational Foundation 2015
Fred Ott Sneeze (Edison Kinetoscopic Record of a Sneeze)
William K.L. Dickson
Coughs and Sneezes
Public Information Films, National Health Service UK
High Speed Footage of Sneezing
Courtesy Prof. Lydia Bourouiba
Welcome Back To School
Fan Turbine Behind A Dark Surface
Vomiting Larry - A demonstration and explanation for his creator
Courtesy Health and Safety Laboratory and Dr. Catherine Makison-Booth
Norovirus EM PHIL 2172 lores
Wikimedia Commons/CDC
Vomiting Machine Face
Grace Tung-Thompson
Fig 2. Photo of a Simulated Vomiting Episode.
Tung-Thompson et al. 2015
Vomiting Machine Whole Thing
Grace Tung-Thompson
Norovirus 4
Wikimedia Commons/Graham Beards


(used with permission from author)
Squeak Pack/squeak_10
Produced by WGBH for PBS Digital Studios


Wikimedia Commons/CDC


Want more info?

William Firth Well’s sneeze powder experiments:

Bourouiba, L., Dehandschoewercker, E., Bush, J.W.M (2014). Violent expiratory events: on coughing and sneezing. Journal of Fluid Mechanics, 745, 537-563. doi:10.1017/jfm.2014.88:

For additional information about the study of respiratory disease transmission via sneezes and its fluid dynamics please visit the MIT Fluid Dynamics of Disease Transmission Laboratory of Prof. Lydia Bourouiba:

Vomiting Larry - A demonstration and explanation from his creator:

Makison Booth, C. (2014). Vomiting Larry: a simulated vomiting system for assessing environmental contamination from projectile vomiting related to norovirus infection. Journal of Infection Prevention, 15(5), 176–180.

To learn more about Vomiting Larry—and lots of other cool projects—visit the UK’s Health and Safety Laboratory site:

Tung-Thompson, G., Libera, D.A., Koch, K.L., de los Reyes, F.L. III, Jaykus, L-A. (2015) Aerosolization of a Human Norovirus Surrogate, Bacteriophage MS2, during Simulated Vomiting. PLoS ONE 10(8): e0134277. doi:10.1371/journal.pone.0134277:

The Vomiting Machine:

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