That is legitimately frustrating... but all it takes is one person traveling through or coming home, then going to work/church/store/whatever, and now it's in your community, and will continue to spread until everyone stays apart.

By the time a test is positive or they end up in the hospital, it's been spreading for a week or two, and now those people are spreading it.

Until we have a vaccine, the best way to fight it is to avoid catching it.