The study included patients who were admitted to hospital with COVID-19 with various complications at Chung Ang University Hospital in Seoul between February and June 2020. The infection was confirmed in patients by PCR testing. The average age of patients was 62 years, 71% were diagnosed with coronavirus pneumonia, more than a third of them needed oxygen support.
All patients were isolated from each other, every two days, doctors took nasopharyngeal swabs for PCR testing using the cycle threshold for the SARS-CoV-2 gene N. In total, the specialists received 156 samples.
“The period from the onset of symptoms to the disappearance of the virus averaged 7 days. The last positive test was obtained 12 days after the onset of symptoms in one of the patients. The rate of positive test results steadily decreased with the increase in the time period from the onset of symptoms, ”the authors reported.
The scientists noted that larger studies are needed to confirm these results, since they used a small sample of hospitalized patients in their work, among whom there were no cases of severe COVID-19. The largest review of 98 studies found that the average duration of coronavirus RNA isolation is 17 days from the onset of symptoms in the upper respiratory tract, 14.6 days in the lower respiratory tract. However, none of the studies detected live viruses in tissues or secretions 9 days after the onset of symptoms. Thus, the peak of the viral load occurs in the first week of the disease, scientists say.
In October, the Centers for Disease Control and Prevention (CDC) reported that viral replication was significantly reduced by the tenth day from the onset of symptoms. In patients with severe COVID-19, the virus can multiply for up to 20 days, but in 95% of cases, this process stops after 15 days.