In Australia, hotel quarantine has caused one outbreak per 204 infected travellers. Purpose-built facilities are far better, but we only have one (Howard Springs, near Darwin) and the federal government has to date refused to build any more.
But no cases of infections slipping thru the testing, no?
Or another framing: The question is, how long is the time between being infected and then infecting someone else? And the answer might be smaller than the time before you show symptoms, but if it’s negative the virus is doing something involving time travel.
They seem to be referring to the serial interval between symptom onset. Which indeed can't be negative on average. But they write it was only negative in 21.6% of cases. And there is no rule stating there can't be cases where it's negative (as long as you have transmission before symptoms).
Or it has a higher viral load.