This article is more than 6 months old

This article is more than 6 months old

Japan has confirmed that a woman who tested negative and left the coronavirus-hit Diamond Princess cruise ship later tested positive, raising more questions about the effectiveness of quarantine measures.

The health minister, Katsunobu Kato, apologised after 23 passengers were allowed to leave the ship without being properly tested and vowed to have people retested.

The woman in her 60s returned home to the Tochigi prefecture north of Tokyo by train on Wednesday, but she had a fever on Friday and tested positive on Saturday, a local official said.

She was the first passenger to have tested positive in Japan after having been cleared to disembark.

Infectious disease experts and local officials have questioned how effective the quarantine period on the vessel was.

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“There has been a judgment that those who disembarked after testing negative had no problem, but it has now become clear that those people can turn positive,” Tochigi’s governor, Tomokazu Fukuda, said on Saturday.

“We call on the government to take additional measures.”

Health minister Katsunobu Kato told a news conference in Tokyo on Saturday that the ministry was trying to reach the 23 passengers for retesting. “We deeply apologise for the situation caused by our oversight,” Kato said. “We will take all necessary measures, like double checks, to prevent a recurrence.”

Japanese authorities said they decided to allow passengers who tested negative during the quarantine period to disembark as they had taken measures to prevent the virus spreading: passengers were confined to their cabins, except for brief outings on open deck when they had to wear gloves and masks and keep their distance from fellow passengers.

However, an infectious diseases specialist from Kobe University, Prof Kentaro Iwata, has said the situation on the ship was “completely chaotic” and violated quarantine procedures, in blunt criticism rarely seen in Japanese officialdom.

He later said he had heard from a colleague on board that quarantine procedures had improved, but he still recommended that all those disembarking should be monitored for at least 14 days and should avoid contact with others.

Since Wednesday about 970 passengers – who tested negative after the government put the ship under quarantine on 5 February – have disembarked, local media reported.

On Saturday about 100 more passengers who had reportedly been in close contact with infected people on board were allowed to get off.

They included the last group of Japanese passengers, while some foreign passengers were still waiting on board for their governments to send chartered aircraft.

With the latest disembarkation, a 14-day quarantine is expected to start for more than 1,000 crew still on board.

Many of them were not placed in isolation as they were needed to prepare food and deliver meals to cabins.

Critics have said that they were inadvertently spreading the virus throughout the ship, which had more than 600 cases of the potentially deadly Covid-19 disease.

Kato defended Japan’s on-board quarantine on Saturday saying there was no medical facility large enough to admit more than 3,000 people at once.