The tests are often not sensitive enough to detect the virus. For example, in Israel they isolated a guy who lived with a confirmed Covid19 patient. It was not until test #3 (on day 12 of isolation, I think) that he came up positive. Testing of asymptotic patients https://twitter.com/jsiwat/status/1247875435595210756

only makes sense in three circumstances: 1) To keep medical staff healthy; 2) To "poll" large populations, to find out in what locales you have an epidemic, in order to move resources there in time to make a difference; and 3) To properly treat at-risk patients. If you are a

doctor, and you have a person from an at-risk category (underlying conditions, etc.) and you realize that a positive test would significantly change the treatment/drugs you would deliver to the patient, then you should test the patient. In any other circumstances, testing

asymptomatic patients is (1) a waste of a precious resource (the test); and (2) a waste of the time of the staff administering and processing the test. We need to be strategic about this.