[Fishbreeder]

An exposed fish or survivor can be detected in some cases as far as four months post exposure. After that it can still be an asymptomatic carrier that tests negative.

If a facility is tested repeatedly each month for a complete cycle (one year) then you might be able to make some kind of statement about it being unlikely to be infected as long as no new fish or unsterilized water has entered the facility. Still, birds, frogs, turtles, etc. can carriy contaminated water, fish eggs, and even fish from infected rivers, infected farms, infected hobby ponds, etc. back to the koi production facility.

Everybody had best go and copy down Ray's post, memorize it and take it straight to heart.