Coronaviruses: establish when a patient stops being contagious

Studies carried out in the first group of those infected with the coronavirus in Germany have established the moment when it is no longer a risk for the population to discharge patients hospitalized for COVID-19, which would allow freeing up space in a situation of scarcity. of beds.

In a joint statement, the Charité clinics in Berlin and Schwabing in Munich, as well as the German Army Institute of Microbiology reveal that the patient is no longer contagious when tests extracted from the nasopharyngeal area and the fluids expelled when coughing show fewer than 100,000 copies of the virus genome.

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The results of the study, carried out in the group infected by the outbreak at the German automobile components company Webasto, indicate in most cases that the viral load in the pharynx had decreased markedly after the first week of illness, in the lung a little later.

Eight days after presenting the first symptoms, experts were no longer able to isolate infectious virus particles in patients despite still detecting copies of the virus genome in the pharynx and lung.

This discovery allows, according to Roman Wölfel, director of the Institute of Microbiology of the German army and one of the main authors of the study, to draw two conclusions. First, "the high viral load in the pharynx immediately with the first symptoms suggests that patients with COVID-19 are soon infectious, possibly even before they realize they are sick," he says.

"At the same time, the infectious capacity of COVID-19 patients appears to depend on the viral load in the pharynx or lung. This is an important factor in deciding when a patient can be discharged at the earliest of shortage of beds and the corresponding pressure of time, "he stresses.

According to these data, the authors of the study, whose results are published in the journal "Nature", estimate that patients infected with COVID-19 can be discharged and go to home quarantine if, ten days after becoming ill, they have in fluids expelled by coughing less than 100,000 copies of the virus genome.

The scientists also determined that SARS-VOC-2 likely multiplies in the gastrointestinal tract, although the presence of infectious viruses in the stool of patients could not be detected. Furthermore, the virus was not detected in the blood and urine of the patients. Furthermore, the blood sera of the patients were analyzed for antibodies against SARS-CoV-2.

Half of the group, which was analyzed for 28 days from the appearance of the first symptoms, had developed antibodies to the virus until the seventh day; two weeks later, all patients had produced antibodies. In turn, with the production of antibodies, the viral load was also slowly reduced.

Already in early February, scientists had revealed that some of the patients analyzed even had a mild symptomatology of the infectious virus in the nasopharyngeal area. "This means that the new coronavirus can multiply in the pharynx without reaching the lung and therefore is very easily transmissible," explains Christian Drosten, director of the Charité Institute of Virology and co-author of the study.

The group of scientists now plans, from this first group of patients but also from other infected patients, to analyze the long-term development of immunity against SARS-CoV-2, data that could contribute to the development of a vaccine.

Source: EFE