tests). 1,570 of those tests were positive for SARS-CoV-2 (1.6%). The majority of people tested on
that day did not have SARS-CoV-2 (98.4% of tests are negative). When only a small proportion of
people being tested have the virus, the operational false positive rate becomes very important.
Clearly the false positive rate cannot exceed 1.6% on that day, and is likely to be much lower. If the
operational false positive rate was 0.4%, 400 of the 1,570 positive tests would be false positives.
That would represent 400 people being isolated when they are well, and much wasted effort in
contact tracing. It is possible that a proportion of infections that we currently view as asymptomatic
may in fact be due to these false positives.