Last year, there were 16 outbreaks on cruise ships, from norovirus, salmonella, E. coli or other unidentified pathogens that cause gastrointestinal symptoms such as diarrhea or vomiting. That's the largest number of cruise ship outbreaks in 12 years.

Centers for Disease Control and Prevention. The majority of these outbreaks were a result of the highly contagious norovirus, the data said, which is spread through direct contact with an infected person,