During a cruise, shaking hands with the captain is a small honor — the shipboard equivalent of shaking hands with the President of the United States. 

Funny thing is, there may come a day when it’s easier to get a handshake from a U.S. President than a cruise ship captain. That’s because on some cruise ships, passengers have been banned from shaking the captain’s hand at formal events.

Writing in Spectator magazine, Charles Moore — the official biographer of the late British Prime Minister Margaret Thatcher — recounts his trip aboard Crystal Cruises’ Serenity. Moore writes that a cruise bulletin informed passengers that shaking hands with the captain at an upcoming passenger/crew meet-and-greet was a big no-no.

"Approximately 80 percent of infections diseases, including norovirus, can be spread via traditional palm-to-palm handshake."

- Dr. John Bradberry

“While the captain is pleased to meet you,“ read the notice, according to Moore, "he and the other staff receiving you refrain from shaking hands in order to provide the most effective preventative sanitary measure.”

This wasn’t the policy of an overly germaphobic captain. Crystal Cruises confirms to Yahoo Travel, it’s the cruise line’s official policy.

"The safety and health of our guests and crew is paramount at Crystal Cruises,” says Crystal spokesman Paul Garcia. He points out the cruise line maintains extensive sanitation measures in accordance with Centers for Disease Control and Prevention (CDC) recommendations. “While the captain is very pleased to meet all our guests,” Garcia says, “he refrains from shaking hands as an additional preventive measure.”

So why all hand-wringing over hand-shaking? You can thank the hysteria over norovirus, that nasty gastrointestinal illness that’s created a nauseauting image problem for cruise lines. Norovirus cases on cruise ships are relatively rare; according to the CDC, there were nine cruise ship outbreaks last year that sickened roughly 1,600 passengers. That’s less than 1 percent of North America’s 11 million cruise ship passengers in 2014, and an even smaller fraction of the 20 million norovirus cases recorded in the U.S. each year.

Still, whenever norovirus does strike a cruise, it makes international headlines, reignites health fears about the safety of cruising and scares past and potential future passengers from stepping foot aboard a ship. As a result, cruise lines spend millions per year to prevent norovirus and the adverse effects the illness has on their bottom lines. In this environment, some cruise lines see anti-handshaking policies as yet another ounce of norovirus prevention that could help avert a ton of negative coverage.

“Approximately 80 percent of infections diseases, including norovirus, can be spread via traditional palm-to-palm handshake,” says Atlanta-area physician John Bradberry, former medical director for Carnival Cruise Lines and supporter of Crystal’s handshake ban. “It’s a sound policy that makes good practical sense from a public health standpoint,” he says. “Policy will not prevent noro, but will significantly reduce the risk.”

Dr. Bradberry points out that a ship’s captain can shake hands with hundreds of passengers at a given formal night or receiving line. If a passenger with norovirus shakes that captain’s hand, Dr. Bradberry says, that risks contaminating not only the captain, but every guest with whom the captain shakes hands — and, subsequently, anyone else those guests touch — throughout the evening.

“The end result is the equivalent of hundreds or more passengers indirectly touching the contaminated hands of hundreds or more fellow passengers,” says Dr. Bradberry. “Avoiding the mass handshakes with the captain is not only for the protection and well-being of the captain, but for the passenger as well.”

Crystal’s not alone in its hand-shaking policy. U.K.-based Fred. Olsen Cruise Lines reportedly also discourages captains from shaking hands during Formal Nights. As for the world’s largest cruise line, Carnival, a spokesperson tells Yahoo Travel it doesn’t ban hand-shaking outright. But “we will instruct our officers to cease hand-shaking at special events (during which they would normally be shaking multiple guests’ hands) if the medical team advises that we are seeing an elevated number of guests with gastrointestinal illness symptoms.”

But there may be some good news for habitual handshakers: other cruise lines don’t seem quite ready to embrace such draconian hands-off policies. A spokesperson for another cruise line tells Yahoo Travel her line has no such policy. She then added, “That’s one I’ve never been asked before.”

Regardless of whether your chosen cruise line bans passenger-captain handshakes outright, when there are outbreak fears, or not at all, experts recommend a better-safe-than sorry approach while on cruise ships — and, yes, that includes handshakes. Dr. Bradberry suggests replacing handshakes with fist bumps. “A fist-to-fist ‘handshake’ is less risky,” he says.

If you’re really afraid of norovirus, you’re probably better off not obsessing over things like handshakes and, instead, paying more attention to the most effective way to stay healthy on a cruise: frequently washing your hands with soap and water (hand sanitizers are less effective but better than nothing). Especially if you plan on shaking the hands of the captain, or anyone else, on the cruise.

“If all people washed their hands promptly after completing a handshake, and especially after a series of handshakes, there would be little to no infectious illness transmission issues,” says Dr. Bradberry. But he adds, “100 percent compliance is simply not going to happen.”

That’s why cruise line are looking at all possible ways to prevent norovirus outbreaks, handshake bans. We can probably expect other eyebrow-raising measures, too, as cruise lines find that media-driven norovirus hysteria is very hard to shake. 

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