Unfortuantly, it struck the Magic. It is probably just that one or two people came down with the illness (remember, anyone anyplace can come down with it) and since it passes so easily, spread to more which gave it to more who gave it to more until it got out of control (ok, spread to about 5% of the passengers and crew). It does its damage - passengers get off - new passengers get on - but the virus is still in the air and repeats itself.
Now, the Carnival ship has been struck - and that was a 3-day cruise. Just must really be brought on by one or two sick people. Odds are - it will happen again. Odds are - it will happen elsewhere because Carnival, Holland America, and all have many, many more ships.
Odds are - it won't happen to Disney for a long time to come.