We recently cruised on the Veendam - 22 days - there was norovirus onboard for most of the cruise. We picked up passengers in San Diego, Seattle and of course a whole shipfull in Vancouver - these passengers were not notified that there was noro onboard and given the choice whether to cruise or not.
My brother-in-law was a captain and he feels that the ships are not performing proper sanitation procedures. he said that it is costly but necessary to avoid things like noro. He never had noro on any of the ships that he sailed with.
By the way, when my husband had noro they called it food poisoning and we were not given any compensation even though he voluntarily quarantined himself until 24 hours after the symptoms disappeared.