WSU Virology

wipe with a wet cloth, and then disinfect with chlorine.

Household bleach, says Duizer, is an average about 5 percent chlorine when new (concentration declines with age), or 50,000 PPM, and thus, can be diluted 50-fold to achieve the 1,000 ppm.

Norovirus is apparently no more resistant to cleaning and disinfection than other pathogens, says Duizer. The virus’ efficiency in causing outbreaks “is more likely due to their extremely low infectious dose

The industrial-size servings of food on a cruise ship with hundreds of passengers can be particularly worrisome, since once the virus enters the food it can spread rapidly. Food can also get more easily contaminated with the virus if it sits out for several hours, as is often the case with buffet-style meals.

And so many people being in one place eases the virus's spread. "In close quarters it doesn't get away, everything's concentrated," Zimring says.

The best defense against gastrointestinal disease, Zimring says, is to wash and sanitize your hands constantly

Over the past five years, an average of about 14 cruise ships a year have had outbreaks of diarrheal illness, and the culprit is almost always norovirus

The best way to avoid it is prevention, and the best prevention is hand washing.

The problem, he said, is passengers. “If Grandma is sick when she gets on, she’s going on the cruise anyway,” Dr. Vinjé said. “And that’s how the virus gets onboard. Then it lands on handrails and doorknobs, and the transmission continues.”