A detailed study of 303 people in South Korea shows that 29% of people infected with the coronavirus never developed symptoms, but carried as many viruses within them as symptomatic people.
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The study, led by Seungjae Lee of Soonchunhyang University and published Thursday in the American journal Jama Internal Medicine, focused on an outbreak of contamination in a South Korean religious group in Daegu, in February. Authorities had decided to place positive cases with few or no symptoms in isolation in a government dormitory building where doctors and nurses meticulously monitored their symptoms, and tested their viral load regularly. The group was young, 25 on average.
Out of 303 people, 89 have never developed symptoms, a proportion of 29%. Since people were locked away until they tested negative, medical staff were able to distinguish pre-symptomatic from true asymptomatic cases. In fact, 21 people initially presented as positive for the coronavirus and without symptoms, but ended up having symptoms. Many studies, testing patients only once, can confuse pre- and asymptomatic cases.
The main lesson is that the virus concentrations in asymptomatic patients were "similar to those in symptomatic patients , " the authors report. But finding residual viral particles in their nose, throat, or lungs doesn't necessarily mean these people were contagious. This is one of the big questions of the pandemic: to what extent are the many asymptomatic cases vectors of the virus? On the one hand they do not cough, but on the other hand they do not place themselves in isolation and are therefore in contact with other people. "It is important to emphasize that the detection of viral RNA is not synonymous with the presence of an infectious and transmissible virus", warn the authors of the study. Large epidemiological and experimental studies are needed to understand this.