Infection with diseases spread by poor handwashing, especially by fecal-borne illness, is extremely common on cruise ships. After my first cruise, when I spent my vacation chilling with high fever and suffering from severe diarrhea, a pharmacist in Miami explained that the crew on foreign-registered ships are mostly from 3rd world countries where concepts like asepsis and handwashing are mostly unheard of. They are cheap labor and willing to spend weeks cooped up on board before a break.
When these 3rd-worlders get together for months on a cruise line, they spread this stuff like wild fire. The unusual part of this story is that it actually reached the press; most do not.
After that first cruise, I have heard this story repeated over and over. I would NEVER go on another cruise with a line that is not subject to U.S. sanitation regulations, as the foreign lines are NOT. If you have gone on a cruise with a foreign-registered boat and not gotten ill, it's because you are very lucky or because you have an exceptional immune system.
Hopefully Carnival Cruise Lines has higher standards for employee health practices.
One wonders if this might have been sabatoge by a disgruntal Haitian employee?