A group of American cruise ship passengers returned to their home port Sunday after being contaminated with the deadly coronavirus.

Fifty American citizens from 11 different cruise lines were exposed to the virus when they disembarked at Halifax, Nova Scotia, with a Royal Caribbean Cruise Line ship that returned from a six-day cruise through the Caribbean, according to the Centers for Disease Control and Prevention.

Most of the passengers are the ill after having been exposed to a Norwegian Cruise Line crew member infected with the coronavirus.

Royal Caribbean spokesman Owen Torres said 10 of the 50 passengers are ill, with a total of 14 having contracted the virus.

Only one crew member is believed to have become infected, according to a report by the Fort Lauderdale Sun Sentinel.

That crew member was being treated in a hospital in Halifax, where the World Health Organization said Friday that it is working with the Canadian government to prevent further outbreaks.

The WHO is helping Canada and local health officials trace the cruise passengers and others who were on the ship, WHO spokesman Tarik Jasarevic said.

His agency and the Canadian government are prepared to consider additional protective measures if needed, the Sun Sentinel reported.

Coronaviruses cause respiratory problems, cold-like symptoms and fatal pneumonia, the CDC says. They’re present in birds, especially in poultry, although the cause of the virus is unknown. A sharp increase in cases worldwide has caused the WHO to declare this year a public health emergency.

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Since October, 90 people from 21 countries have been infected with coronavirus. Six have died.

Among the victims were travelers who had close contact with sick people in Saudi Arabia, where the current outbreak originated. The other 45, according to WHO, were infected at hospitals where patients had been treated or developed at least three of the symptoms of the virus: fever, shortness of breath, muscle aches and headaches.

Cal State Fullerton health science professor Lisa McCarthy said she is still concerned about the increasing virus cases.

"The spike in cases was certainly one thing that concerned me, as was the fact that it was finding new places where it could emerge," McCarthy said. "Certainly the door is open for more disease to become global."

The CDC has issued health-risk guidelines for the cruise ship passengers. Those include washing hands with soap and water for 20 seconds, staying away from sick people and wearing surgical masks.

That's pretty much the same advice the CDC gives when people are traveling with someone who has a contagious disease, said medical epidemiologist DeWayne Pitts of the CDC.

"We are so concerned with what's going on in the U.S. that I don't know what to make of the idea that we might start making some common sense suggestions for what we do when we go on vacation," he said.

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