The Wide Path of a Sneeze

Droplets in sneezes and coughs traveled much farther than expected

(RxWiki News) Germ-filled drops of liquid blow everywhere when a sneeze or cough isn't covered. Just how far those drops can blow was not known until now.

Coughs and sneezes spread respiratory diseases from infected people to people who are susceptible to the germs. To help understand the spread of germs by sneezes and coughs, a research team from MIT first wanted to know how far the particles in a sneeze or cough could travel.

They found that coughs and sneezes actually produced clouds of droplets of different sizes. The smallest droplets were suspended in the cloud and traveled the greatest distances. Some even stayed airborne long enough to reach ceiling ventilation units.

"Sneeze or cough into a disposable tissue or your elbow."

This research was conducted by Lydia Bourouiba, PhD, and John W. M. Bush, PhD, from the Department of Mathematics at the Massachusetts Institute of Technology in Cambridge, MA, and Eline Dehandschoewercker, a graduate student at ESPCI ParisTech in Paris, France.

These researchers used actual sneezes and coughs produced by adults, special high-speed imaging of coughs and sneezes, laboratory simulations and mathematical models to examine the droplets in coughs and sneezes.

They found that sneezes and coughs were actually explosive bursts that resulted in a cloud containing droplets of germs. The droplets were different sizes and their size determined how far they traveled. Droplet particles fell from the cloud at different times that were partly determined by their speed in relation to the speed the whole cloud was moving.

Older estimates of how far droplets in these explosive bursts traveled were based on an assumption that the particles in a cough or a sneeze were all separate and disconnected.

This study by the MIT team found that droplets that were 100 micrometers (millionths of a meter) in diameter traveled five times farther than previously estimated, and droplets 10 micrometers in diameter traveled 200 times farther than estimated.

The droplets that were under 50 micrometers in diameter could stay airborne for the longest distances, and some traveled far enough to reach the ceiling and contaminate ventilation systems, up to four to six meters (13 to 20 feet).

The researchers found that the volume of particles blown out by a cough ranged from one quarter of a liter to over 1 liter in females and was over a liter and a half in males. The clouds produced by sneezes were more dense than those made by coughs. The distance large droplets traveled was farther in a sneeze than a cough.

Dr. Bush explained that we can often see the droplets in a sneeze or a cough, but there is actually a cloud of gases that spread out much farther than the droplets we can see or feel.

Talking about germs, the authors commented, "It would thus clearly remain suspended in a cough or sneeze cloud metres away from the cougher."

The MIT News Office's report on the research stated, “The tendency of these droplets to stay airborne, resuspended by gas clouds, means that ventilation systems may be more prone to transmitting potentially infectious particles than had been suspected.”

The reported continued, “With this in mind, architects and engineers may want to re-examine the design of workplaces and hospitals, or air circulation on airplanes, to reduce the chances of airborne pathogens being transmitted among people."

In response to this study's findings, Sylvia Suarez-Ponce, RN, infection control practitioner at Loyola University Health System commented, “Many think they are doing the best thing by sneezing into the crook of their arm, or covering their mouth with their hand when they cough.”

She recommended using a tissue for both coughing and sneezing. “Throw the soiled tissue away and then wash your hands really, really well,” she said.

The crook of your elbow is second best, and hand sanitizing gel can also be effective, but only if used as the manufacturer directs, Suarez-Ponce said.

The MIT team’s research was published in the April issue of the Journal of Fluid Mechanics.

The National Science Foundation provided funding for the research.

Review Date: 
April 17, 2014