< Propagation

How can we reduce the contagion in enclosed spaces: schools, colleges, places of business, and public transport?

Text updated on 2021-04-15


Current knowledge of coronavirus transmission by aerosols and sputum and salivary tests allow for effective measures to be taken to protect oneself from coronavirus and not to contaminate others.

Barrier to coronavirus: mask and ventilation

To limit the transmission of SARS-CoV-2, the virus of the COVID-19virus, it is necessary to know that this coronavirus is transmitted mainly by aerosols and droplets (see the question Is the coronavirus SARS-CoV-2 transmitted by aerosols?). The aerosols are micro-droplets containing particles of SARS-CoV-2 and they are produced when we breathe, speak, eat, sing, etc. Depending on their size, these micro-droplets will disperse more or less. Droplets with a diameter greater than 5 µm, called sputters, will fall to the ground fairly quickly around the person who produced them (1 or 2 m around the person). Aerosols with a diameter of less than 5 µm can remain suspended in the air for hours. They "float" in the air and can be found within seconds of the person who produced them, much like cigarette smoke. To avoid being contaminated by viral aerosols, you must wear a well-fitted mask (see the question Why wear a mask?) that will filter them. Another way to protect yourself is to limit the quantity of viral aerosols in a closed space by airing the room with outside air (see the question What precautions should be taken in the workplace to limit airborne transmission of the virus?).

Because of this transmission by viral aerosols, closed places are much more at risk. To limit the spread of the coronavirus, it is necessary to open the windows in classrooms, offices, and cafeterias, but also in public transport (metros, buses, RER, trams). And it is necessary to schedule meetings outside and not to eat with these comrades or colleagues in poorly ventilated spaces

Detecting infected people before symptoms: saliva tests

To limit the transmission of the coronavirus, the other important point to know is that one can be contagious without having symptoms. On average, 50% of people will not have symptoms and, therefore, will never know that they are infected. On the other hand, even without symptoms, they can be contagious and transmit the coronavirus to other people (see the question Can a person without symptoms contaminate other people?). And for the 50% of the persons who are going to have symptoms, they are contagious 2 to 3 days before the appearance of the symptoms, i.e.,they will begin to be able to transmit the coronavirus 2 to 3 days before taking a test.

One way to detect contagious individuals, whether or not they have symptoms, is to test all students in a school or college, or all employees in a company on a routine and frequent basis, for example, once a week. This requires that individuals adhere to the protocol and are willing to be tested frequently. Nasopharyngeal testing is unpleasant and no one wants to be tested once a week. On the other hand, salivary tests or nasal swabs are not painful and can easily be performed by all age groups, even the youngest (see the question Which swab to test for COVID-19 : nasopharyngeal or oral?).

Pooling methods can reduce the costs of these tests without reducing their effectiveness (see the question What approaches could accelerate large-scale screening?). Saliva pooling methods are now routinely used in the United States, notably in New York State. Frequent salivary testing is an effective way to stop the spread of coronavirus and to detect infected people before they infect others.


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Sources

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Study of a pooling strategy for the detection of SARS-Cov-2 in saliva samples applied to a population of 400,000 school children in New York State. The study reveals an increased contamination during the Halloween and New Year's holidays.

Chongfeng Bi et al. bioRxiv Pooled Surveillance Testing Program for Asymptomatic SARS-CoV-2 Infections in K-12 Schools and Universities, bioRxiv (February 2021)

Further reading

Do I have to wear a mask if I don't have any symptoms?

Why put on a mask?

What precautions should be taken in the workplace to limit airborne transmission of the virus?

Is the SARS-CoV-2 coronavirus transmitted by aerosols?

What approaches could accelerate large-scale screening?

Why can measuring CO2 levels help us fight COVID-19 ?

What sample to test for COVID-19: nasopharyngeal or buccal?