Correlation Between 3790 Quantitative Polymerase Chain Reaction - Positives Samples and Positive Cell Cultures, Including 1941 Severe Acute Respiratory Syndrome Coronavirus 2 Isolates

"The outbreak of the coronavirus disease 2019 (COVID-19) pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was declared a pandemic on 12 March 2020 by the World Health Organization. A major issue related to the outbreak has been to correlate viral RNA load obtained after reverse-transcription polymerase chain reaction (RT-PCR) and expressed as the cycle threshold (Ct) with contagiousness and therefore duration of eviction from contacts and discharge from specialized infectious disease wards. Several recent publications, based on more than 100 studies, have attempted to propose a cutoff Ct value and duration of eviction, with a consensus at approximately Ct >30 and at least 10 days, respectively. However, in an article published in Clinical Infectious Diseases, Bullard et al reported that patients could not be contagious with Ct >25 as the virus is not detected in culture above this value...

Since the beginning of the epidemic, we have performed in our institute 250,566 SARS-CoV-2 RT-PCR for 179,151 patients, of which 13,161 (7.3%) tested positive... It can be observed that at Ct=25, up to 70% of patients remain positive in culture and that at Ct=30 this value drops to 20%. At Ct=35, the value we used to report a positive result for PCR, < 3% of cultures are positive."