Earlier quoted context omitted.
No detectable virus means no transmissible virus.
To reiterate the question, why is that?
Infection requires virus particles to be physically present in transmission vectors (fluids, droplets, etc). There's generally also a dose-response effect where more particles means more chance of evading the immune system well enough to establish replication in the victim.
So a lack of anything to detect, means a lack of anything to spread an infection.