Outbreaks at sea are one of the oldest problems in public health. From medieval plague quarantines to modern times, they have repeatedly tested the ability to control infectious disease – and have played a key role in shaping the international public health framework in place today.

Buffets and shared spaces help make cruise ships ideal places for viruses to flourish, disease experts say. Still, Americans are booking cruises in record numbers.

Are they unique hotbeds of illness? Let’s look at the research.