PHNOM PENH (NYTIMES) - The cruise ship had been shunned at port after port for fear it might carry the coronavirus, but when the Westerdam arrived in Cambodia last Thursday (Feb 13), the Prime Minister greeted its passengers with flowers.

Amid assurances that the ship was disease-free, hundreds of elated passengers disembarked. Some went sightseeing, visiting beaches and restaurants and getting massages. Others travelled on to destinations around the world.

One, however, did not make it much farther than the thermal scanners at Kuala Lumpur airport in Malaysia. The passenger, an American, was stopped last Saturday, and later tested positive for the coronavirus.

On Sunday, with passengers already headed for destinations on at least three continents, health officials were scrambling to determine how a big a problem they now have - and how to stop it from getting bigger.

"We anticipated glitches, but I have to tell you I didn't anticipate one of this magnitude," said Dr William Schaffner, an infectious disease specialist at Vanderbilt University Medical Centre.

With more than 1,000 passengers from the Westerdam headed for home, Dr Schaffner said, it may be harder than ever to keep the coronavirus outbreak contained to China.

"This could be a turning point," he said.

It is unclear how well the passengers were screened before they were allowed off the ship. But the best approach to containing a broader spread of the virus from the Westerdam would be to track down all of the passengers and quarantine them for two weeks, experts said.

It won't be easy.

Dr Peter Rabinowitz, co-director of the MetaCenter for Pandemic Preparedness and Global Health Security at University of Washington, said the episode would test the limits of contact tracing, the method used to track down people exposed to infection.

"It's really daunting to control a situation like this now that people have gone all over the world," Dr Rabinowitz said.

More than 140 passengers from the ship flew to Malaysia, and all but the US woman who tested positive and her husband were eventually allowed to continue on to their destinations, including the United States, the Netherlands and Australia, officials said.

More 1,000 other passengers took charter flights to Phnom Penh, the capital of Cambodia, and were in various stages of transit home, the cruise line said.

When the Westerdam set sail from Hong Kong on Feb 1 for a 14-day cruise, the Holland America Line cruise ship was carrying 1,455 passengers and 802 crew members.

TROUBLED WATERS

It docked in Kaohsiung, Taiwan, on Feb 4, but then soon ran into trouble.

With the eyes of the world on Yokohama, Japan, where the virus was spreading among passengers and crew members trapped on another cruise ship, the Diamond Princess, ports on the Westerdam's itinerary began denying it entry.

Taipei said no. So did ports in Japan, the Philippines, Thailand and the US territory of Guam, according to local news reports and passengers on board.

Last Thursday, with Holland America insisting that no one on the Westerdam was infected, Cambodia agreed to let it dock.

In Cambodia, the cruise line found a country whose leader, closely allied with Chinese officials, has cast doubts on the seriousness of the coronavirus outbreak, which has infected some 68,000 people and killed more than 1,600 in China.

"Is there any Cambodian or foreigner in Cambodia who has died of the disease?" Prime Minister Hun Sen said earlier this month. "The real disease happening in Cambodia right now is the disease of fear."

And last Friday, US President Donald Trump tweeted his thanks to Cambodia for allowing the ship, carrying more than 600 American passengers, to dock.

But by opening his arms to Westerdam, Mr Hun Sen may have put his own citizens at risk.

As of Sunday, 233 passengers and 747 crew members were still on the ship docked at Sihanoukville, Cambodia, Holland America said. After Malaysia's announcement that a passenger was infected, the remaining passengers and crew members were restricted to the ship, and buses that had been scheduled to transport them remained parked nearby.

It was unclear whether Cambodia would seek to quarantine passengers who are still in the country, or whether those who had left by plane would face quarantine in their own countries when they arrived.

On Sunday, Malaysia's Deputy Prime Minister Wan Azizah Wan Ismail said at a news conference that the American woman confirmed to be infected after she left the ship had tested positive twice for the virus.

The woman, 83, and her husband, 85, also a US citizen, were both hospitalised and in isolation. The husband has also been tested twice for the virus, and the results were negative both times. But he has pneumonia, which is often a sign of the virus that appears before it can be identified through testing.

DIFFERING STANDARDS

The global fight against the coronavirus is complicated by the fact that different countries may have different levels of disease surveillance and prevention measures.

While the World Health Organisation provides guidance, it is up to each country to enforce these standards, including whether to quarantine people who may have been exposed or to stop them from travelling.

The Cambodian government said passengers and crew members on the Westerdam had been screened using protocols from the WHO and the US Centres for Disease Control and Prevention before being allowed to disembark.

One passenger said Cambodian health officials had taken everyone's temperature.

About 20 people who had reported being sick during the trip were also tested for the coronavirus, according to a statement issued on Sunday by the US Embassy in Cambodia. All of them tested negative.

The American woman was not among them. She did not visit the ship's medical centre during the cruise to report any symptoms of illness, Holland America said in a statement on Sunday.

Dr Schaffner, the infectious disease expert, said it might have been wiser to test each disembarking passenger instead of a select group because other screening methods - like travel questionnaires and taking temperatures - are fallible.

People eager to get off a ship may not respond entirely truthfully to questioning, and sick people's temperatures vary during the day, he said, generally being lower in the morning.

When the American passenger first tested positive, both Holland America and Cambodia questioned the result, and requested further testing and confirmation. Malaysia carried out a second round of testing, and said on Sunday that it had confirmed that the woman was infected. It remains unclear, however, when she was infected, where or by whom.

Datuk Seri Wan Azizah said that the country would not accept any more passengers from the Westerdam.

Coordination between Malaysia and Cambodia appears to have been minimal. In a letter seeking more information from his Malaysian counterpart on Sunday, the health minister of Cambodia, Mr Mam Bunheng, said he had learned through the news media that the first test of the American woman had been positive.

Attempts to contact Cambodian officials for comment were not immediately successful.

Holland America said in its statement on Sunday that no other passengers or crew members had reported any symptoms and that passengers who had returned home would be contacted by their local health departments.

The company defended the health screening it had conducted during the cruise and on arrival in Cambodia. But it did not respond to a question on whether it had been appropriate to let Westerdam passengers travel to many parts of the world without putting them in quarantine first.