Royal Caribbean is one company going beyond the CLIA guidelines and denying boarding to any passenger who has come within six feet of anyone who has been in mainland China, Hong Kong, Macau, Iran, South Korea or Italy within the last 15 days. The company will be relying on passengers to be truthful about any close encounters.

To comply with these regulations, passengers are filling out health and travel questionnaires before they board. “Cruise companies always screened passengers for health, but the questions are more specific now to the virus,” said Ms. Shelton.

Preboarding temperature checks are also becoming more common.

After a meeting in Florida on Saturday with executives from top American cruise lines, Vice President Mike Pence said that he has asked the cruise industry to work closely with the Department of Homeland Security, the Coast Guard, and the Centers for Disease Control on a cruise industry-led effort enhance entry and exit screenings for passengers and crew members on cruise ships and to establish shipboard testing for the coronavirus over the next 72 hours.

“New quarantining standards will be coordinated with the CDC for all ships and we also will be working with the industry as they develop a plan to move any patients who contract the coronavirus or otherwise become seriously ill to land-based facilities,” Mr. Pence said.

The vice president added that he expected the cruise industry and the administration to announce progress made in these efforts early next week.

What about changing itineraries?

Companies have been canceling some sailings, adjusting the itineraries of others, and in some cases moving to their next scheduled part of the globe a bit early. Seabourn, for example, canceled one cruise departing from Singapore, and replaced another ship’s Asian ports of call with Australian ones. Alaska cruises are expected to start up a bit earlier than usual for Viking and some other lines.

Cruise companies have always reserved the right to change their schedules based on local circumstances. A letter posted Feb. 12 on the Celebrity Cruise company website states that a March 17 cruise will embark from Dubai instead of Singapore, replace the stop in Thailand with a day at sea, and extend days in India. The letter states that “normal cancellation penalties will apply.” For a passenger two to four weeks from departure, the penalty is 75 percent of the trip cost.