Sick on board

We recenlty returned from a cruise. We were asked NOT to board if we had a cough. If you started coughing on board, see the ship's doctor. There were hand sanitizers everywhere. Staff were at every restaurant, directing you to use them. Staff cleaned and polished railings and handrails continuously. Yet, on cruise message boards, I note that people who caught the flu blame it (somehow) "on the ship", not the passengers. Fascinating!