In winter times we rely more frequently on test to find out about sickness. Covid-19 testing has proven pretty effective in this respect. Often it is preferable to test more persons positive if at the risk of having many false positives. False negative tests can have many fatal consequences. Hence we have to weigh the risks of both kinds of false tests. This applies to many other diseases and diagnoses as well. There is no certainty but only a probability of each of the test results. The true result may deviate from the observed or tested result. FF FT TF TT are the possible outcomes of (1) the underlying true or false outcomes, which can have test scores of true or false as well. Not much new here the rest is statistics or probabilities to be more precise.
The overall outcome of testing or true sickness for some only God may know. Cancellations of events may be the result of one or the other reasoning.