I know two people who were on this cruise; one took ill, and the other's spouse took ill.
One of them noted that she saw another passenger drop a set of tongs on the floor at the buffet and attempt to put it back into the food. She didn't succeed, as other pax stopped her. Just one example of how customers are often to blame for unsanitary conditions, and how this can happen anywhere. This is one reason I avoid buffets whenever possible, or limit my choices to only those served by crew members.
Handwashing is the best defense, but must be done regularly.