You can earn some credibility holding back a woman’s hair while she vomits; you can lose credibility when a 2-year-old vomits all over the car seat, and then while attempting to clean it up, you vomit in response, like in Stand By Me (see below).

I’ve done both.

Researchers from the U.S. Centers for Disease Control investigated a 2009 outbreak on a cruise ship and concluded infected passengers were significantly more likely to have an ill cabin mate, and to have resided or dined on the deck level where a vomiting incident had occurred during boarding.

That’s right: someone barfed while passengers were boarding the ship and just watching and trying to contain that little bit of throw-up that just happened in your mouth was a statistically significant risk factor.

Questionnaires about when people did or did not seek medical care, hygiene practices, and possible norovirus exposure were placed in every cabin after the outbreak began. The ship had 1,842 passengers on board, and 83 percent returned the questionnaires. Of the 15 percent of respondents who met the case definition for acute gastroenteritis, only 60 percent had sought medical care on the ship.

Less than 1 per cent of the crew reported illness, and their low attack rate may have been due to the few crew members who had direct contact with passengers. This included separate sleeping and dining areas and alternate passages for boarding and exiting the ship.

"Cruise line personnel should discourage ill passengers from boarding their ships," according to study author Mary Wikswo, MPH, of the Centers for Disease Control and Prevention. "Once on board, passengers and crew who become ill should report to the ship’s medical center as soon as possible. These quick actions are crucial in preventing the introduction and spread of norovirus on cruise ships and allow ship personnel to take immediate steps to prevent the spread of illness."

What I conclude, based on this and other studies, including our own, is that telling people to wash their hands has almost no effect — and that the best way to control the spread of norovirus – on cruise ships, in restaurants, in schools – is to break the infection cycle because these noroviruses are crazy infective: stay home, isolate yourself, tie your hair in a bun, and barf away.