Prevention

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• Other symptoms of COVID-19 are improving (exception: loss of taste and smell which may persist for weeks or months after recovery and need not delay the end of isolation). (Note that these recommendations do not apply to immunocompromised persons or persons with severe COVID-19. Find more information at https://bit.ly/3qB62IR [CDC]). Health authorities should know that SARS-CoV-2 infected individuals do not need to be quarantined for weeks. Persistently positive RT-PCRs generally do not reflect replication-competent virus. SARS-CoV-2 infectivity rapidly decreases to near-zero after about 10 days in mild-to-moderately-ill patients and 15 days in severely-to-critically-ill and immunocompromised patients (Rhee 2020). Of note, RT-PCR cycle threshold (Ct) values (a measure for viral load) correlated strongly with cultivable virus. In one study, the probability of culturing virus declined to 8% in samples with Ct > 35 and to 6% (95% CI: 0.9–31.2%) 10 days after onset; it was similar in asymptomatic and symptomatic persons (Singanayagam 2020). A meta-analysis of 79 studies (5340 individuals) concluded that no study detected live virus beyond day 9 of illness, despite persistently high viral loads (Cevik 2020). In individuals who had mildly or moderately symptomatic SARS-CoV-2 infection and who present no symptoms for at least two days, a positive RT-PCR test 10 days or more after the first symptoms does not indicate infectiousness (‘post-infectious PCRpositivity’; Mina 2020). In most countries (for example, Germany, USA), health authorities do not require a negative SARS-CoV-2 RT-PCR test to end the quarantine. Autorities in Italy or other countries that even in late November continued quarantining people at home for two, three, four weeks or longer because of continuously positive RT-PCR results should take note.

Find a detailed discussion of SARS-CoV-2 prevention in the corresponding chapter on page 117. For everyday life, the following five rules of thumb are helpful: 1. Avoid crowded places (more than 5-10 people). The more people are grouped together, the higher the probability that a superspreader is present who emits infectious particles tens or hundreds times more than a ‘normally’ contagious individual. Avoid funerals, and postpone religious services including weddings, baptisms, circumcisions, as well as team sports and choir singing until after the pandemic.

Transmission | 97

2. Avoid in particular crowded and closed spaces (even worse: airconditioned closed places where ‘old air’ is being moved around). In a room where a SARS-CoV-2 infected individual is coughing frequently, viable virus can be isolated from samples collected 2 to 4,8 meters away. Strangers or unacquainted persons should not meet in crowded or closed spaces. 3. Avoid in all circumstances crowded, closed and noisy spaces where people must shout to communicate. Shouting or speaking loudly emits a continuous flow of aerosols that linger in the air for minutes. Intimate conversation in a noisy and crowded room, with people shouting at one another at a distance of 30 centimeters, inhaling deep into theirs lungs the exhalations of the person they are speaking to/shouting at for 5, 10, 20 minutes or longer is, from the virus’s point of view, the best conceivable transmission setting. Noise from machines or music around people grouped in a closed environment also creates the perfect setting for a superspreader event. 4. Outside crowded, closed or noisy spaces, keep a distance of 2 meters to other people. 5. Always wear a fask mask in public spaces. A face mask is a highly effective low-tech solution that can help contain local SARS-CoV-2 outbreaks. Face masks are not new to medicine – surgeons have been using them for more than a century. Next time you are unhappy when wearing a face mask, watch this video and enjoy the fact that unlike the doctors who might one day treat you for COVID-19 or other ailments, you won’t never have to put on and remove protective gear in a hospital. Those who doubt the effectiveness of face masks might extract precious information from Figure 2. The cumulative number of confirmed COVID-19 cases in different countries – presented per million population – is intriguing. What did Japan, South Korea, Taiwan and Vietnam right that the other countries didn’t? The most probable explanation is • Better testing • Efficient contract tracing and isolation • Early use of face masks