The contamination caused by a sneeze has been captured on video, and it’s scary
Noel Brandon Kelsch, RDH, RDHAP, MS
I always wondered why people say “gesundheit” or “bless you” when you sneeze. Gesundheit, a German term, is an expression to wish good health. My daughter, Serena, explained the mystery. Two of the main symptoms of the plague of were coughing and sneezing. Pope Gregory the Great was thought to suggest that “God bless you” being stated would protect the person from sudden death.
With recent information from MIT, that may not be a bad idea. Using high-speed videos, researchers have captured some enlightening footage that clarifies the movement of the cloud that forms from a sneeze.
Researchers at MIT revealed “that as a person sneezes, they launch a sheet of fluid that balloons, then breaks apart in long filaments that destabilize, and finally disperses as a spray of droplets, similar to paint that is flung through the air.”1
According to Scientific American, there is purpose in our sneezing. It is an autonomic-physiologic response to the irritation of the respiratory epithelium lining of the nose. The process is more complex than you might think. It usually starts with the release of chemicals such as histamine or leukotrienes. Your nose knows! For example, eosinophils and masts cells found in the mucosal lining reacts to the presence of a viral respiratory infection, filtered particles, allergens, etc. This lead to fluid release from vessels in the nose, thus that age-old nasal drip and congestion.
In the midst of all this, the nerve endings in the nose send a note to the brain telling it to jump in. First a little itching, and then an activation of nerve endings of the head and neck, resulting in rapid expulsion of air. The reason this air is so high in velocity is because the airflow is achieved by closing off the vocal cords and a buildup of pressure inside the chest. The swift opening of the cords allows the pressurized air to flow back up the respiratory tract to expel the irritants with an accelerated blast. The purpose of the blast is to get those particles out of the nose.
The problem is that it also facilitates the spreading of pathogenic matter.2-5
The research at MIT is valuable not only to the public but especially to the medical setting where those with symptoms congregate. In this research, researcher recorded over 100 sneezes from healthy patients. They were able to capture a visual demonstration of what happens in that fraction of a second that the fluid is expelled from the nose and mouth and “flung” into the air we all breathe. A very large percentage produced the same paint-like pattern of fluid fragmentation. There were some slight alterations, such as the “more elastic the fluid, or saliva, the longer the fluid traveled before breaking into droplets.”
It has long been thought that a sneeze results in a simple uniform spray of droplets. Lydia Bourouiba, assistant professor in the department of civil and environmental engineering and head of the Fluid Dynamics of Disease Transmission Laboratory at MIT stated that this was one of the most important parts of the study. “Having a better idea of how sneezing disperses droplets can help researchers map the spread of infections through the environment, as well as identify individuals who may be super spreaders. It also can help to understand each individual person and their inner physiology.”
The study found after analyzing more than 100 sneezes immediately after exiting the mouth, the exhaled fluid can form a wide sheet that “balloons” with the simultaneous expelling of air. As it travels through the air, the balloon bursts into thin filaments that eventually separate into individual droplets of various sizes that ultimately fall to the ground or remain suspended in the turbulent cloud. This cloud is an important factor. For example, the smaller droplets that emerge in a cough or sneeze may travel five to 200 times further than they would if those droplets simply moved as groups of unconnected particles. This sheet supplies the element to allow the particles to move.
The team also observed an interesting variation. For subjects with more elastic saliva, the expelled fluid tended to stay in filament form longer, forming beads along the filaments that eventually slid off as droplets allowing the material to travel further.
Further studies from MIT showed us that 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. It is clear that this “multiphase turbulent buoyant cloud” is fluid in motion and can contaminate a very large area and even move into a ventilation system.
So, what does this mean for you in the health care setting? Here are a few tips.
Basic protocols: Stay away from people who are sneezing, clear the room after a sneeze, and air it out. If you feel a sneeze coming on in the operatory, leave the operatory. If someone sneezes or coughs in the operatory, after they leave follow the same universal/standard precautions you follow for cleaning and disinfecting all surfaces.
OSHA cough etiquette: For the public setting, we are to cover coughs and sneezes with a tissue, or cough and sneeze into your upper sleeve(s). Dispose of used tissues in “no-touch” wastebaskets.6
I would also note that you do not cough or sneeze into your lab coat. If that becomes necessary, change it immediately.
Keep sick workers/patients home: Follow the CDC recommendation and OSHA regulations. Those who have fever and respiratory symptoms should stay home until 24 hours after the fever ends (without medication). It’s also important to note that fever does not occur in all cases; runny nose, aches and pains, diarrhea, and vomiting can all mean the flu is occurring. All offices should have a policy that allows sick employees to stay home without penalty.6 Reschedule elective treatment for patients who are sick, coughing, or sneezing.
Here’s hoping no one has to say gesundheit or bless you to you.
NOEL BRANDON KELSCH, RDH, RDHAP, MS, is a syndicated columnist, writer, speaker, and cartoonist. She serves on the editorial review committee for the Organization for Safety, Asepsis and Prevention newsletter and has received many national awards. Kelsch owns her dental hygiene practice that focuses on access to care for all and helps facilitate the Simi Valley Free Dental Clinic. She has devoted much of her 35 years in dentistry to educating people about the devastating effects of methamphetamines and drug use. She is a past president of the California Dental Hygienists’ Association.
1. http://news.mit.edu/2016/sneezing-fluid-cascade-not-simple-spray-0210 Accessed April 3, 2018.
2. https://www.scientificamerican.com/article/why-do-we-sneeze/ Accessed April 3, 2018.
3. Tang JW, Liebner TJ, Craven BA, Settles GS. A schlieren optical study of the human cough with and without wearing masks for aerosol infection control. Journal of the Royal Society Interface. 2009;6(6):S727–S736.
4. Jennison MW. The dynamics of sneezing—studies by high-speed photography. The Scientific Monthly. 1941;52(1):24–33.
5. Posada JA, Redrow J, Celik I. A mathematical model for predicting the viability of airborne viruses. Journal of Virological Methods. 2010;164(1-2):88–95.
6. https://www.osha.gov/dts/guidance/flu/nonhealthcare.html Accessed April 3, 2018.