A cruise ship has been quarantined on the Caribbean island of St. Lucia due to a confirmed case of the measles, but NYU medical professor Dr. Marc Siegel said the best thing the passengers can do is keep their cool.

The quarantine of nearly 300 passengers aboard the ship has taken place among a nationwide outbreak of measles, as nearly 700 cases have been reported across the United States.

There has only been one case confirmed on the ship, named "Freewinds," but the disease is highly contagious and can spread quickly among those unvaccinated. The infected person aboard is reportedly in stable condition.

During an appearance on "America's Newsroom" on Friday, Dr. Siegel said that it's not uncommon for infections to break out on cruise ships, because they hold a large number of people in close quarters and are often not adequately disinfected.

DR. MARC SIEGEL: MEASLES QUARANTINE ON A CRUISE SHIP - WHAT ARE CHALLENGES FOR PASSENGERS?

Although the measles outbreak and quarantine in St. Lucia is cause for alarm, Dr. Siegel, who authored the book "False Alarm," said that most people diagnosed with the virus end up being fine.

"This isn't the time I'm going to go on TV and warn about those rare complications of the measles or warn about hospitalization," he told host Bill Hemmer.

In this case, he says, those on the ship would do well to have some "diversionary activity" to take their minds off of the stress, such as exercising in an area that is measles-free.

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"If you are on the boat the best thing you can do is realize that the vast majority of the time if you've got measles, you would recover uneventfully. And also go out on the balcony, look out on the ocean," he added.