r RT PCR;
Uses chemical to strip out everything that might interfere. RT then changes target virus RNA into DNA since PCR only works with DNA.
PCR then thermal cycles this, doubling any DNA present each time, typically 35 times. 2^35 = 35 billion.
The reagents include a target marker which emits die on encoutering target DNA.
In real time RT PCR, this is checked each cycle and so you can stop when you have the confidence you need.
In non real time, you just wait till the end of the number of cycles, then check dye levels.
The test takes a long time to develop since you have to get the cleaner, the RT, the target, dye etc all 'correct'.
The amount and timing of the dye relates to quantitivity.
But how can you possibly say that someone who has the virus in them isnt 'infected'? The only way to do this is to set accurate infection load (by immune system response) or accurate symptom levels (coughs per minutes - again dependant on each individual sensitivity to cough response), or things as absolutely ridiculous as that.
Oh, and you would have to swab everyone absolutely the same despite different physical characteristics and fluid dynamics in their throat, nose and the rest.
We have a system and then the 'statistics' are relevant to that system, until we understand the systems better and can interpret them better.
The real question is; at what viral load does an asymptomatic person shed sufficient viruses, in which conditions, such that people of known sensitivity will receive sufficient viral load. And how does this change with incubation etc over time.
See how difficult this is?