Understanding #COVID-19: what does viral RNA load really mean? - The Lancet Infectious Diseases
It is noteworthy that the presence of viral RNA in specimens does not always correlate with viral transmissibility.
In a ferret model of H1N1 infection, the loss of viral culture positivity but not the absence of viral RNA coincided with the end of the infectious period. In fact, real-time reverse transcriptase PCR results remained positive 6–8 days after the loss of transmissibility.
For SARS #coronavirus, viral RNA is detectable in the respiratory secretions and stools of some patients after onset of illness for more than 1 month, but live virus could not be detected by culture after week 3.11
The inability to differentiate between infective and non-infective (dead or antibody-neutralised) viruses remains a major limitation of nucleic acid detection. Despite this limitation, given the difficulties in culturing live virus from clinical specimens during a pandemic, using viral RNA load as a surrogate remains plausible for generating clinical hypotheses.