Piralla A, Ricchi M, Cusi MG, Prati P, Vicari N, Scarsi G, Gandolfo C, Anichini G, Terrosi C, Percivalle E, Nepita EV, Bergami F, Tallarita M, Di Martino R, Ferrari A, Rovida F, Lunghi G, Schiavo R, Baldanti F. Residual SARS-CoV-2 RNA in nasal swabs of convalescent COVID-19: is prolonged quarantine always justified? Int J Infect Dis. 2020 Oct 29:S1201-9712(20)32278-5. doi: 10.1016/j.ijid.2020.10.072. Epub ahead of print. PMID: 33130202.

Real-time RT-PCR is currently the most sensitive method to detect severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). Defining whether a patient could be contagious or not in the presence of residual SARS-CoV-2 RNA is of extreme importance in the context of public health. In this prospective multicenter study, virus isolation was prospectively attempted in 387 nasal swabs from clinically recovered patients yet showing low viral load (>30 quantification cycle). The median Cq value was 37.0 (range 30.0 to 39.4). Overall, cytopathic effect was detected in 9 samples corresponding to 2.3% (9/387) of culture positivity rate. Results of this study help to dissect between true virus replication and residual viral RNA detection in recovered patients.