By Friday, nearly 1,000 passengers who had tested negative for the COVID-19 virus had disembarked from the Diamond Princess cruise ship after a quarantine period came to a close.

But rather than representing a positive turning point in the two-week saga, a growing number of questions are now being raised over the government’s decision not to isolate the passengers allowed to leave the ship and its failure to test some others during the quarantine period.

News emerged Saturday that a Japanese woman who was allowed to leave the cruise ship last week was confirmed to have been infected after returning to her home in Tochigi Prefecture despite an initial negative test result, according to local officials.

The central government is separately under fire for failing to test 23 passengers — 19 Japanese and four foreign nationals — during the two-week quarantine period.

“I deeply regret our mistake. We will do our utmost not to repeat a similar mistake,” health minister Katsunobu Kato told reporters Saturday.

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The Tochigi woman was the first person found to have been infected with the pneumonia-causing virus out of a total of 969 people who disembarked from the ship over the three days through Friday. During a two-week monitoring period through Wednesday, she had tested negative for the illness.

After leaving the vessel docked in Yokohama with her husband on Wednesday, the woman traveled home using public transport. She wore a surgical mask while traveling, according to the prefectural government.

But the Tochigi woman wasn’t the only one who returned home unsupervised. There were others who, like her, used public transport to return to their homes or go to hotels.

Japan’s handling of the situation contrasts sharply with the more stringent isolation measures taken by other countries. As many as 800 non-Japanese nationals flew back home via state-chartered flights, but American travelers, for example, were later placed under an additional two weeks of quarantine in military facilities to eliminate the risk of further infections.

In fact, some countries, such as Australia and the U.S., saw a few of those who were repatriated develop the COVID-19 infection, including those who had tested negative before disembarking the ship. Kato said the health ministry has confirmed that 25 foreign passengers — 18 Americans, six Australians and one Israeli — were infected with the virus.

Before the Tochigi woman’s case surfaced, Koji Wada, a public health studies professor at the International University of Health and Welfare, was already sounding an alarm over the possibility that some of the infected could slip through the cracks, even after testing.

“Testing on the ship isn’t perfect. There is no guarantee that it (the tests) can detect every single one of those infected,” said Wada. “It’s possible that some of those who disembarked the ship could develop the infection in Japan, too,” he added.

Health minister Kato, for his part, explained Friday that the decision to let passengers disembark was a “tough judgment call.” Although he was aware of the risk that some may develop infections after leaving the ship, the minister said he also had to take into account the growing criticism — both at home and abroad — over the long confinement of the passengers.

The government gave the passengers who tested negative for the virus a document confirming their cleared status. It also asked them to refrain from going outside for “nonessential” purposes and to monitor their temperatures on a daily basis.

Also at issue is what to do with the nearly 1,000 crew members still on board the Diamond Princess.

A National Institute of Infectious Diseases study has shown that the virus was able to spread among crew members because they were not quarantined under the same strict conditions as the passengers, even after they were told to stay in their rooms. The government is requesting that the crew members undergo a two-week monitoring period.

But it is widely seen as difficult to transport the crew members to shore-based facilities or order them to stay in their rooms because they are needed to operate the Diamond Princess.

Kato said the ministry is “making arrangements with the ship operator” regarding what to do with the crew members.

There are also passengers still remaining on board, the vast majority of whom are non-Japanese awaiting the arrival of government-chartered flights from their home countries to bring them back.

Atsuo Hamada, a professor of travel medicine studies at Tokyo Medical University, said he, for one, agrees with the government’s decision to disembark the passengers.

“Now that infections have started to spread across the nation, there is no point in further quarantining those on the ship,” Hamada said.

What is now needed at this stage of the crisis is to “direct more manpower and resources to efforts to prevent the further spread of the virus nationwide and develop better medical infrastructure,” he said.

RELATED PHOTOS A passenger heads for a temperature check after disembarking from the Diamond Princess cruise ship in Yokohama on Friday. | AFP-JIJI

Katsunobu Kato | KYODO