Norovirus on cruise ships

There is always lots of negativity about virus’s on cruise ships, more so than any other hotel or holiday accommodation.
Recently I had to look into this on behalf of a customer who was very apprehensive about booking an excellent deal we had offered them on an Oceania cruise.
What I was told was that the reason why certain ships are often reported as having the virus is because by law cruise lines have to declare it if a certain percentage of passengers on board are taken ill.
Therefore the larger ships often do not have to declare anything because the ratio of passengers on board are much higher so they never reach the percentage that they need to declare.
Unfortunately smaller ships like Oriana, Fred Olsen and Oceania Marina who carry smaller numbers so often have to declare it which makes it look like they have a continual problem on board when in fact they don’t..
This seems very misleading and very unfair to these smaller ships who I am sure follow all of the same regulations as the larger vessels.
Unfortunately it is usually the passengers who bring the virus on boards. We often see people visiting the buffets and restaurants without sanitising their hands.
I am pleased to say that this did put my customers minds at rest and I am sure they are now looking forward to a wonderful 5* luxury cruise.