Residual SARS-CoV-2 RNA in nasal swabs of convalescent COVID-19 patients: Is prolonged quarantine always justified?

A. Piralla, M. Ricchi, M.G. Cusi, P. Prati, N. Vicari, G. Scarsi, C. Gandolfo, G. Anichini, C. Terrosi, E. Percivalle, E. Vecchio Nepita, F. Bergami, M. Tallarita, R. Di Martino, A. Ferrari, F. Rovida, G. Lunghi, R. Schiavo, F. Baldanti

Research output: Contribution to journalArticlepeer-review


Real-time reverse transcription 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 contagious 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 showing low viral load (quantification cycle, Cq, value greater than 30). The median Cq value was 36.8 (range 30.0–39.4). Overall, a cytopathic effect was detected in nine samples, corresponding to a culture positivity rate of 2.3% (9/387). The results of this study help to dissect true virus replication and residual viral RNA detection in recovered patients.

Original languageEnglish
Pages (from-to)299-302
Number of pages4
JournalInternational Journal of Infectious Diseases
Publication statusPublished - 2021


  • COVID-19
  • Cq value
  • Infectivity
  • Real-time reverse transcription PCR
  • SARS-CoV-2
  • Virus isolation
  • virus RNA
  • convalescence
  • coronavirus disease 2019
  • cytopathogenic effect
  • human
  • immunofluorescence
  • limit of quantitation
  • major clinical study
  • multicenter study
  • nose smear
  • observational study
  • prospective study
  • quarantine
  • real time reverse transcription polymerase chain reaction
  • RNA sequencing
  • Severe acute respiratory syndrome coronavirus 2
  • Short Survey
  • virus detection
  • virus genome
  • virus isolation
  • virus load
  • virus pathogenesis
  • virus replication
  • adult
  • diagnosis
  • disease exacerbation
  • female
  • genetics
  • isolation and purification
  • male
  • middle aged
  • nose
  • physiology
  • real time polymerase chain reaction
  • time factor
  • virology
  • young adult
  • Adult
  • COVID-19 Testing
  • Disease Progression
  • Female
  • Humans
  • Male
  • Middle Aged
  • Nose
  • Prospective Studies
  • Quarantine
  • Real-Time Polymerase Chain Reaction
  • RNA, Viral
  • Time Factors
  • Viral Load
  • Young Adult


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