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Discontinuation of isolation for persons with COVID-19: Is 10 days really safe?

Background. The detection of SARS-CoV-2 RNA by real-time polymerase chain reaction (PCR) in respiratory samples from COVID-19 patients is not a direct indication of the presence of viable viruses. The isolation of SARS-CoV-2 in cell culture system however, can acts as surrogate marker of infectiousness. Cell culture based studies performed mostly with hospitalized and moderate/severe COVID-19 claims that no replication competent virus is found after 9 days of the symptoms onset in respiratory samples. Therefore, it is now recommended 10 days isolation before patient discharge. Methods. We cell-cultured 29 SARS-COV-2 RT-PCR positive respiratory samples at the 10th day after the illness in Vero E6 cells. After two passages, cytopathic effect and cycle threshold (CT) lower than the obtained in the original sample were used to determine positivity. Findings. We found viable particles in (7/29) 24% of samples tested. The positivity in cell culture was strongly associated (p<0.0001) to the low cycle thresholds in clinical samples (Ct <21). Conclusion. This data adds important knowledge to the current protocols for de-isolation of patients with non-hospitalized mild COVID-19.