2.1 How is COVID-19 transmitted?
By Scott Tytheridge
One of the first lines of defence preventing pathogens from entering the human body can also become one of the ways the coronavirus (SARS-CoV-2) moves between people. Cells in the nose and running along the trachea called goblet cells create
mucus which can trap pathogens and prevent them from moving further down the respiratory tract. When we sneeze, cough or even breathe and speak we release tiny droplets of this mucus plus saliva and cells (Figure 1). If a person is infected with
respiratory virus such as the one that causes COVID-19 then these droplets can contain the infective virus.
Figure 1. A sneeze in progress. This photo reveals the plume of salivary droplets as they are expelled when a person sneezes, and illustrates the need to cover the nose and mouth when coughing and/or sneezing to prevent the spread of droplets, and protect others from infection.
According to the current evidence [1, 2], we know that the virus causing COVID-19 is primarily transmitted between people through these respiratory droplets.
When a person infected with the virus coughs or sneezes, the infective droplets are launched through the air (Figure 2). Droplet transmission occurs when a person is in close contact (e.g. within 1 metre) with someone
who is infected with the virus. The distance is important, because once emitted, the droplets rapidly fall to the ground. This means that people standing further away from the infected individual won’t be exposed to airborne droplets.
Figure 2. Examples of respiratory transmission routes: droplet, airborne, direct contact & indirect contact .
Respiratory droplets can land on surfaces and inanimate objects such as doorknobs, telephones and tables. These surfaces are referred to as ‘fomites’. We touch our faces (eyes, nose, mouth) a lot – some studies have recorded 16  to
 times per hour. If our hands touch the fomites, get contaminated with the infective droplets and then we touch our face, the virus can spread inside our bodies. This is referred to as ‘indirect contact’
because it is not directly from an infected person.
The infective virus can survive on fomites from hours to days: evidence shows that the virus can survive on stainless steel and plastic surfaces for up to three days, but will survive less well on surfaces like
Transmission can also occur if we touch an infected person directly and then touch our face. This is referred to as ‘direct contact’ (Figure 2).
Figure 3. Virus titer of SARS-CoV-2 on different surfaces. X axis shows hours after application. The virus survives for longer on stainless steel and plastic than other surface types.
That brings us to the end of this step. In this step, we have learnt that the COVID-19 virus can be transmitted by airborne droplets, direct contact and through contact with fomites (Figure 2). Both transmission from fomites and direct contact
are through our hands which is why it is so important to wash our hands frequently. This will be discussed in the next step.
Fomites: Objects or materials which are likely to carry infection, such as clothes, utensils, and furniture.
Goblet cells: Cells in the lining of the airways that produce mucus to trap dust and pathogens.
Pathogen: Microorganism that causes disease.
Respiratory: Of or involving the respiratory system (nasal cavity, trachea, lungs etc.).
Respiratory virus: a virus that infects the respiratory system
Transmission: The spreading of pathogenic disease, for example by touch, food, water.
Virus: An ultramicroscopic infectious non-cellular organism that can replicate inside the cells of living hosts, often with negative consequences.
For further reading, check out the BBC bitesize section for Communicable disease transmission. https://www.bbc.co.uk/bitesize/guides/z83qfcw/revision/2
Also have a look at the info pack by Hans and Dr. Dog for handy tips on staying safe. https://www.twinkl.co.uk/resources/twinkl-partnerships/london-school-of-hygiene-tropical-medicine-partnerships
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Figure 1. Gathany J. CDC Public Health Image Library. 2009 Jan.
Figure 2. van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, Tamin A, Harcourt JL, Thornburg NJ, Gerber SI, Lloyd-Smith JO. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of
Medicine. 2020 Apr 16;382(16):1564-7. Accessed via: https://www.journalofhospitalinfection.com/article/S0195-6701(15)00367-9/fulltext
Figure 3. van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, Tamin A, Harcourt JL, Thornburg NJ, Gerber SI, Lloyd-Smith JO. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of
Medicine. 2020 Apr 16;382(16):1564-7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7121658/