Droplet Transmission Through Sneezes 

A sneeze, or sternutation, is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa membrane (Encyclopedia Britannica, 2015).

During a sneeze, the soft palate and palatine uvula depress while the back of the tongue elevates to partially close the passage to the mouth so that air ejected from the lungs may be expelled through the nose (Mygind, 1997). Due to a partially closed mouth, a large amount of the air is also expelled from the mouth. The force and extent of the expulsion of the air through the nose varies. One study found that a single sneeze may produce an exit velocity of a maximum of 4.5 metres per second (Tang et al 2013).

Researchers used an LED lighting system with a high-speed camera to capture the spread of germs from coughing and sneezing. Source: Bourouja, 2016

A single sneeze can produce up to 40,000 droplets (Somogyi et al, 2004). When assessing the airborne survival of bacteria in aerosol droplets from coughs and sneezes, researchers found that the average sneeze would send around 100,000 contagious pathogens into the air (Fernandez et al, 2019). These pathogens can carry viruses such as influenza (Inouye, 2006) and respiratory syncytial virus (RSV) (CDC, 2018). The most critical time for the spread of those pathogens is in the first few minutes after a sneeze or cough occurring (Ip et al, 2007).

After a sneeze, the cloud of droplet-containing gas can remain suspended in the air for prolonged periods of time depending on its size. Researchers found that bioaerosol droplets (having a diameter less than the width of a human hair) can remain in the air for a period lasting two weeks (Bourouiba, 2016). These suspended droplets pose a risk to the infection spreading when accidentally inhaled into the body. The Centers for Disease Control and Prevention (CDC) recommends opening windows to allow ventilation throughout a room (CDC, 2020).

When these droplets fall onto a surface, virus transmission can occur if a person touches these surfaces and then rubs their face. Research shows that we tend to touch our faces frequently, about 16 times an hour (Nicas and Best, 2008). It is important for people to frequently wash their hands with soap and water.

Preventative Measures

The CDC recommends covering your mouth and nose with a tissue when sneezing and then disposing of it immediately. Remember to wash your hands after a sneeze. If you don’t have access to soap and water, use an alcohol-based hand sanitiser with a minimum of 60 to 80 per cent alcohol solution on your hands thoroughly for a minimum 20 seconds.

Other recommendations to stop the spread of germs include wearing a face mask when out in public. Face masks can effectively reduce the spread of infectious viruses by preventing droplets dispersing into the air. The below video demonstrates what happens when you talk, cough or sneeze compared with not wearing a mask, wearing different layered cloth masks and wearing a surgical mask.

You can be infected with the coronavirus, but not show symptoms. So you cannot identify an infected person just by looking at them. And you may be infected (and infectious) but not know it .We wanted to compare how effective different types of masks were at preventing outward transmission of droplets while talking, coughing and sneezing. These are the types of masks the public might use to reduce community transmission.

The results clearly show that a three-ply surgical mask is the most effective at blocking droplets and aerosols from talking, coughing and sneezing.  If you cannot obtain one, the CDC has video instructions on how to make a good cloth face mask.

A single-layer cloth face covering also reduced the droplet spread caused by speaking, coughing and sneezing but was not as good as a two-layered cloth mask or surgical mask.

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Reference

Bourouiba, L., 2016. A Sneeze. New England Journal of Medicine, 375(8), p.e15. https://www.nejm.org/doi/full/10.1056/NEJMicm1501197

CDC 2020. Coughing And Sneezing | Etiquette &Amp Practice | Hygiene | Healthy Water | CDC. [online] Available at: <https://www.cdc.gov/healthywater/hygiene/etiquette/coughing_sneezing.html> [Accessed 29 July 2020].

CDC. 2018. RSV | Transmission And Prevention | Respiratory Syncytial Virus | CDC. [online] Available at: <https://www.cdc.gov/rsv/about/transmission.html> [Accessed 29 July 2020].

Encyclopedia Britannica. 2015. Mucous Membrane | Function, Examples, Locations, & Facts. [online] Available at: <https://www.britannica.com/science/mucous-membrane> [Accessed 29 July 2020].

Fernandez, M., Thomas, R., Garton, N., Hudson, A., Haddrell, A. and Reid, J., 2019. Assessing the airborne survival of bacteria in populations of aerosol droplets with a novel technology. Journal of The Royal Society Interface, 16(150), p.20180779.doi: 10.1098/rsif.2018.0779

Inouye, S., Matsudaira, Y., Sugihara, Y., 2006 Masks for influenza patients: measurement of airflow from the mouth. Jpn J Infect Dis 59: 179–181.

Ip, M., Tang, J., Hui, D., Wong, A., Chan, M., Joynt, G., So, A., Hall, S., Chan, P. and Sung, J., 2007. Airflow and droplet spreading around oxygen masks: A simulation model for infection control research. American Journal of Infection Control, 35(10), pp.684-689. DOI: 10.1016/j.ajic.2007.05.007 

Mygind, N. and Dahl, R., 1998. Anatomy, physiology and function of the nasal cavities in health and disease. Advanced Drug Delivery Reviews, 29(1-2), pp.3-12. doi: 10.1080/15459620802003896

Somogyi, R., Vesely, A., Azami, T., Preiss, D., Fisher, J., Correia, J. and Fowler, R., 2004. Dispersal of Respiratory Droplets With Open vs Closed Oxygen Delivery Masks. Chest, 125(3), pp.1155-1157. DOI:https://doi.org/10.1378/chest.125.3.1155

Tang, J., Nicolle, A., Klettner, C., Pantelic, J., Wang, L., Suhaimi, A., Tan, A., Ong, G., Su, R., Sekhar, C., Cheong, D. and Tham, K., 2013. Airflow Dynamics of Human Jets: Sneezing and Breathing – Potential Sources of Infectious Aerosols. PLoS ONE, 8(4), p.e59970.doi: 10.1371/journal.pone.0059970