to get the factual information about norovirus. Note that it is a common thing and the failure by passengers and crew to use basic personal hygiene is the reason it spreads. Since the crew is typically more driven to wash their hands frequently, it is reasonable to blame most outbreaks on the passengers - including those who are sick and still insist on boarding the ship. Those who fail to wash after using the toilet and then rush to the buffet and grab the ladles, etc.
Once it spreads it is hard to kill because of the small enclosed environment of a ship.