"You're never going to get rid of them," Dr. Frederick Southwick, chief of infectious diseases at the University of Florida College of Medicine, says of such outbreaks. He calls a ship the "perfect vehicle" for transmitting the so-called Norwalk-like virus, suspected in the most recent cases.
"You've got a large number of people in a small environment," he says. The virus spreads rapidly by person-to-person contact. Typically, you get infected when you touch an infected surface, then your mouth. Just one ill person on board can infect many other passengers, he says. [end quote] Source.