How do we determine incubation period if the infection can be transmitted asymptomatically?

Question

How do we know that Person B was infected by Person A, unless Person B went into quarantine directly after interacting with Person A? If they don’t go into quarantine, how do we know that a random Person C didn’t interact with them and cause the infection?

And for the vast majority of infections that can’t be contact traced like the example above, how do we determine the date they were actually infected if the disease can be transmitted asymptomatically?

In: Biology

Answer 1

Also, there have been at least two incidents now where one person (accidentally) infected a lot of people at once, so in those cases it was pretty obvious.