TOKYO (Reuters) - Two elderly American passengers, quarantined in Japan with the new coronavirus, learned on Wednesday they were still carrying the virus even after their expected quarantine period had ended.

Their reaction: a shrug and grin.

Clyde and Renee Smith, both 80, were separated from their grandsons and taken off the Diamond Princess cruise ship in the port of Yokohama and hospitalised after testing positive for the virus on Feb. 3.

They told Reuters they did not have thoughts harsher than surprise when they learned they are still stuck in quarantine because they are on a U.S. no-fly list until they are virus-free.

“We are very happy here,” Clyde said from the couple’s hospital room in western Tokyo. “They’re taking excellent care of us. This is the newest, fanciest hospital I’ve ever seen,” he said, adding that the doctors and nurses “are the friendliest and nicest I could imagine.”

Public health officials have said the incubation period for the virus was 14 days, but the Smiths were still positive in a test taken on Monday, two weeks after their initial test.

Otherwise healthy carriers can harbour and transmit a virus without experiencing symptoms. Such carriers have played a role in spreading typhoid, influenza and HIV.

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Scientists have been closely watching for such cases among patients with the new coronavirus. On Tuesday, the U.S. Centers for Disease Control and Prevention (CDC) cited the high rate of infections among patients without symptoms as a reason for ordering an additional 14 days of quarantine for all passengers and crew removed from the cruise ship before they can travel to the United States.

The Smiths will be tested every 48 hours and must get two negative results before they can leave quarantine.

The news that they were still testing positive was “a little bit unnerving,” Renee said, but only because they have things they want to tend to back in Atlanta.

The Smiths said their vital signs have been normal throughout and they have shown no symptoms of the disease, called COVID-19, which has killed over 2,000 people - the vast majority in the region of central China around the epicentre in the city of Wuhan.

Japan’s public-health response to the outbreak aboard the Diamond Princess - the biggest outside China - has been heavily criticised.

The CDC, headquartered in the Smiths’ hometown, said Tokyo’s quarantine may not have been sufficient, while a Japanese infectious-disease specialist who had visited the ship as a volunteer doctor said the quarantine was run by “bureaucrats” who stoked the crisis by failing to follow basic protocols.

But the Smiths supported Japan’s response and understood the need for them to remain in quarantine until they are free of the virus.

“This is so new and unprecedented that I don’t think the medical community has any current, firm knowledge of what’s going on there,” Clyde said, adding that Japan was doing its best “to prevent a real pandemic worldwide.”

Renee, with a broad smile, added, “so we’re being unwilling guinea pigs.”