I take RCCL cruises often. Almost always have a good experience. There was one time in 1987 (my honeymoon) where my bride and I got violently sick for a 2-3 day period. I'm pretty sure it was the raw fish we had during a midnight buffet. But we'll never know for sure. And we had no idea if others got sick too. But the crew of the ship were phenomenal during that time. They felt bad we got ill and were always checking on us and bringing us food to our cabin. When we felt better, they slipped us an envelope of gift certificates to use at the next port of call.
We never complained and ended up becoming loyal customers of the line as a result of how great they handled the situation.
Probably was the raw fish. As a rule, when away from home, I will avoid any uncooked food. There was a recent episode of several people getting sick from eating raspberries in a high end restaurant.
Raw fish can cause more harm than just vomiting/diarrhea for a few days. I saw on reality TV, one man ate sushi and got infected with parasites which made a home in his eye, causing all sorts of problems.