Contact tracing and testing. A very sick person is tested and hospitalized and then they test everyone they have been in contact with... and some of them come up positive but they no or very weak symptoms.
Thank you!
Correct, and at least 2 important factors should be noted:
1) S. Korea has done a lot of this testing, tracing, and more testing, and exceptionally effectively because they have the most astounding, and scary, surveillance and tracing of civilians that one could ever hope to never come here. It's Orwellian on steroids, enhanced by technology Orwell could have scarcely imagined.
2) S. Korea's sample set is by now large in numbers, quality, and covers several weeks time. Extensive follow ups can determine if asymptomatic persons ever develop symptoms, and whether they still manage to infect others such as relatives, despite precautions.