< 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, windows should be opened in classrooms, offices, canteens, but also in public transport (metros, buses, RER, trams). And you should prefer to meet outside and not eat with your friends or colleagues in poorly ventilated areas.

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 people, whether or not they have symptoms, is to test systematically and frequently: for example, once a week among all students in a school or college, or among all staff in a company. 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 every week. On the other hand, saliva tests or nasal swabs are not painful and can easily be done 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.

Sources

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