On the occasions where I have had to be tested for TB the only contact I had with the infected person was from the podium at the front of an 80 seat lecture hall. Everyone signed up for the course was tested, whether they had attended the class or not. Of the 76 tested, 2 students showed positive on the TB skin test (about the average for the same number of people tested randomly for TB) but both were subsequently cleared by x-ray and blood tests. However, 5 persons in another class the original vector had been in tested positive on the skin test and 4 were confirmed to have TB. Those four were immediately placed in treatment and each became another vector for contact tracking. I was mildly inconvenienced by the test but relieved at the result. I ran into one of those who tested positive a year or so later and they were grateful they had been tested and gotten into treatment before any serious symptomology developed.

Contact tracking, intentionally spreads a wide net and with luck a high number of negative tests, and few positives. Some false positives are inevitable given the limits of testing. The worst possible testing outcome is a false negatives as that prevents the infected person getting into treatment and they continue to unwittingly spread the disease. Sadly some (many? most?)of the testing methodologies being used for COVID-19 are proving to be "unreliable" resulting in high levels of both false negatives and false positives.


If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein