My parents both had it back in August with mild symptoms. My mom tested positive again about 2 weeks ago and because it had been 94 days (4 days past some seemingly arbitrary 90 day timeframe), it was treated as a second case and she was told to quarantine a second time and forced to miss work. She had no symptoms this time around (though I know people can transmit without presenting symptoms). I wish there would have been some kind of transparency regarding the second positive test, like what's the "viral load" to trigger a positive test, was it lower than her "viral load" the first time? Is there even a threshold for that for people who tested positive before? I'm not too educated on how these tests work.
I'm all for taking this seriously, but there's still so much we don't know about it and so much that's hard to account for. Just don't assume that people won't test positive again just because they've had it once already as it seems to be an inexact science at this point.
The tests we have right now, at least none of the ones I've seen, have viral loads. Its a positive or negative. There are three types of tests we have right now:
1) PCR- basically it detects viral DNA. Theoretically we could figure out viral titers with this, but with a nasopharyngeal swab... but it would probably be a useless number. Viral titers are useful for blood stream infections (like HIV, HCV) but not so much for airway infections.
2) ELISA- Testing for viral proteins directly
The two above test for active (or "recent" infections. 90 days might be a relatively arbitrary time frame, but it could also be based on data that I haven't seen).
3) Antibody test- this is a test to see if you've developed an immune response. This does NOT necessarily mean you are immune. You probably are. But its not a gamble I would take at this stage.
94 days is a significant delay between positive tests, but it is seen. It could represent a second infection or it could represent residual viral particles from the prior infection. There have been a few proven 2nd infections, but its an arduous process to PROVE, and something thats only been done to add to the medical literature on the topic. But we have seen multiple cases of true 2nd infections in immunocompetent (healthy) people.
The unfortunate reality is that we know very, very little still. Even with all the gains we've made in the past year, each step we take is a totally new step forward.