I realize you don't make the rules. I also realize that the common sense you exhibit is not always present at checkpoints.

As you point out, a checkpoint is anything but sterile and cross-contamination can happen (it can also happen in a so-called 'sterile' environment - witness recent events in a quarantined government facility where a dangerous 'superbug' got loose).

IMHO, when a test is positive, it should be standard procedure to immediately rerun the test with explicit attention to the possibility of contamination - ie, TSO removes gloves, sanitizes hands, gets a new set of gloves from a different box/location, tests gloves in machine, if clear, swabs pax and re-tests.

This should, IMHO, be the first step after any 'positive'. It's the sort of 'first step' many professionals in other lines of work take when a test comes up positive. The 'first step' should not be to force the pax into a mandatory backroom unwitnessed, unphotographed frisk of body and belongings, accompanied by a report on the pax that becomes a permanent part of a that individual's government record.