In Taiwan we didn’t practice mass testing because among 395 cases, only 55 were locally transmitted, and the infection source could not be traced in only ten cases. If many cases have no known infection sources then you have to do mass testing. But it is sometimes neither efficient nor cost effective. You have to test [patients’] close contacts as a first priority, then high-risk groups – healthcare workers, supermarket cashiers, taxi and public transport drivers. If they aren’t infected then others won’t be.