SHARES
“Lately, our government is reopening various lock downs and controls, imposed to reduce the risks of COVID-19 spread. On one hand, we are happy to be able to open up businesses and enjoy many services. We are glad to be able to meet family and friends in spite of the restrictions and limitations However, some of us are also worried if this would lead to even worse viral spread. My office has so many common shared space and items such as stationery, office ware, pantry amenities etc.” Ling worries about her health and that of the people around her.
In fact, COVID-19 spreads more readily in closed indoor spaces as compared to public open spaces. In view of this, the current method of social distancing (staying 6 feet away from others) may not work in situations where we spend long hours in an enclosed space.
The Virus Spread Formula
In an article written by Professor Erin Bromage, with the title “The Risks – Know Them – Avoid Them”, he describes successful infection as a direct result from exposure to sufficiently huge amount of coronavirus or for a long enough duration.
Successful Infection = Exposure to Virus x Time
With reference to past pandemics caused by similar coronaviruses, namely MERS and SARS, we know roughly that it takes about 1000 virus particles to infect a person. On a cautionary note, more studies are needed to fully understand how COVID-19, which is caused by SARS-CoV-2 virus, spreads and infects a person. Yet, we can learn from these past studies to simulate how coronavirus can spread from a person to another. With better understanding, we can take precautionary steps, to reduce the risks of COVID-19 spread, during this period of loosening movement restrictions.
Virus Exposure
SARS-CoV-2 infects a person through the airway. The virus replicates itself into many many copies in our body. It is then being released out into the environment through respiratory droplets during coughing, sneezing, talking and even breathing. These virus-containing droplets can stay in the air and get inhaled by another person. Otherwise, it falls onto surfaces and the ground. However, this is not the end of the story yet. We may touch these surfaces with our body parts such as our hands. Afterward, by touching our eyes, nose and mouth, we carry the virus to our airway.
Risks of COVID-19 Spread
Risks of Covid-19 spread depends directly on the type & period of exposure and virus count. All these three are contributory factors to the viral load. The higher the viral load exposure, the more likely to contract the infection.
Sneeze & Cough
According to research data from past pandemics, we know that a single sneeze and cough can release up to 2 hundred million virus particles. Remember, we need only 1000 virus particles to infect a person. Therefore, a single sneeze and cough can readily infect almost everyone within 6 feet distance or in a small enclosed space. Hence, wear mask and stay at least 6 feet apart from others to prevent virus spread.
Recent studies show how far coughs travel, when you sneeze and relative to any covering used:
Breathing
Breathing can release up to 33 virus particles per minute. Yet, the exact number for the SARS-CoV-2 virus is still unknown. However with this knowledge from past studies of other coronavirus, we know that breathing the same air with an infected person may not cause virus spread immediately. For instance, passing by an asymptomatic person within 6 feet, or taking an elevator with an infected person without symptoms. Even so, if we stay long enough, it takes about 30 minutes for us to get infected if we happen to breathe in the same air. For example, you may be sitting in the same car, bus or train for 30 minutes or more, or breathing the same air in an enclosed office or restaurant, etc.
Talking
Speaking releases about 10 times more virus particles compared to breathing (~200 virus particles per minute). In this context, speaking face-to-face with an infected person for 5 minutes or more can easily cause virus spread.
Image showing how air conditioning in a restaurant causes COVID-19 spread only on one side of the room. A1 is the index case with no symptoms. The dinner took about 1 hours. Photo by Lu JY et al. from CDC.
Where Are The Places With Risks Of COVID-19 Spread?
Although common advice includes stay home and avoid public places, COVID-19 usually spreads indoor. This can be your home, office, public transport, restaurants, supermarkets etc. In open spaces with large amount of air and good air circulation, the virus particles can get diluted easily, making it less likely for us to be exposed to sufficiently high dose of virus particles for long enough duration. Even then, you should still wear your mask and keep your distance. After all, all it takes is one cough or sneeze within 6 feet to put you at great risk of infection.
Risk of Covid-19 Spread
On top of that, do not forget surfaces. All droplets produced will eventually fall to the ground and surfaces. They can stay alive for hours to days outside of human body. Although current data are showing that surface-spread of virus does not play a big role in COVID-19 pandemic, this may be due to good hand hygiene practice. Keep it up! Wash your hands often with soap and water. You may use a hand disinfectant if your hands are not visibly soiled. Remember, never touch your eyes, nose, and mouth with unwashed hands.
Photo by Hughes Songe from Flickr
Conclusion
According to research results from similar pandemics in the past caused by MERS and SARS, we can devise preventive steps ahead to slow the spread of COVID-19. Although our understanding on this new strand of virus is still limited, current measures such as social distancing, lock downs, wearing face mask, good hand hygiene are working well in controlling virus spread. Keep it up everyone! May we brave through this pandemic together!
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References:
1. Bromage E. The risks – know them – avoid them [Internet]. Erin Bromage PhD: Disease musings. 2020. (Available from: https://www.erinbromage.com/post/the-risks-know-them-avoid-them; last updated on 2020 May 7; last accessed on 2020 Jul 4)
2. Lu JY, Gu JN, Li KB, Xu CH, Su WZ, Lai ZS et al. COVID-19 outbreak associated with air conditioning in restaurant, GuangZhou, China, 2020. Emerging Infectious Disease.2020 Jul 7;26(7):1628-31. https://dx.doi.org/10.3201/eid2607.200764
by Chang Xian
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