A South Korean citizen who tested positive for Covid-19 after travelling from New Zealand spent more than 14 hours in an airport transit lounge.

Health authorities in South Korea believe the person was likely infected during transit at Singapore’s Changi Airport after leaving Christchurch on July 21, according to the Ministry of Health.

They arrived in South Korea on July 22, and returned a positive result for Covid-19 after being tested on arrival. They were not showing symptoms at the time.

Health Minister Chris Hipkins and director-general of health Dr Ashley Bloomfield both said on Tuesday that health authorities here were basing their response on a “worst-case scenario” – that the person was infectious while in New Zealand.

They were taking this approach out of an “abundance of caution”, Hipkins said, as there was no evidence of community transmission in the country.

Five people who lived with the person in Auckland were all well, but were self-isolating. They will be tested on Tuesday.

They have been interviewed for contact tracing purposes, but New Zealand health authorities are yet to speak to the person in South Korea.

Before leaving New Zealand, the person travelled from Auckland to Christchurch on July 20 on flight NZ0555. They stayed in accommodation in Christchurch for a night before taking the international flight.

People in the two rows immediately around the person on the domestic flight are being treated as close contacts and being asked to self-isolate and be tested.

Bloomfield said 170 contacts had so far been identified, including those on the flight. Health workers had attempted to contact all of them, and had already had conversations with the “vast majority”.

Of the close contacts on the domestic flight, Bloomfield said all but one had been spoken to.

The person left Christchurch on Tuesday July 21 on Singapore Airlines flight SQ298, a spokesman for the airline confirmed. The flight departed at 10.57am and arrived in Singapore at 17.01pm local time.

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They left Singapore on Wednesday July 22 on Singapore Airlines flight SQ600. The flight departed at 8.10am and arrived at Incheon International Airport, near Seoul, at 14.44pm local time.

Singapore Airlines was working closely with health authorities in Singapore, South Korea and New Zealand to assist with contact tracing, the airline spokesman said.

Crew on the flights who worked in the cabin area where the customer was seated had been placed on leave and were monitoring their health for 14 days.

“The aircraft that operated these flights have been fogged and have undergone a deep clean, including air filter and seat cover changes.”

A Christchurch Airport spokeswoman said voluntary coronavirus tests had been offered to airport staff on duty when the flight departed.

A ministry spokeswoman confirmed the person was tested on arrival at their final destination in South Korea. The ministry was formally notified of the test result on Saturday.

“South Korean authorities have informed us that based on their initial investigations they suspect the traveller was infected during the transit in Singapore airport,” the ministry said in a statement on Monday.

“A false positive is extremely unusual, but sample collection and laboratory error can occur, and cross contamination is always possible,” he said.

Stuff has approached the Embassy of the Republic of Korea to New Zealand for comment about South Korea’s testing protocols.

Hipkins said on Monday the Government had requested a second test be done on the person to make sure the result was correct.

“We’re working with South Korea to obtain the information we need to do other contact tracing in New Zealand, simply as a precaution,” he said.

University of Otago, Wellington professor of public health Michael Baker said the incubation period for the virus had a wide range but was typically four to five days.

“The lower end of the range is probably very short. It’s usually quoted as two days, but that could be as little as 25 to 48 hours.”

Baker said it was appropriate a second test be done.

“A false positive is extremely unusual, but sample collection and laboratory error can occur, and cross contamination is always possible,” he said.

Given the absence of any evidence of community transmission in New Zealand, Baker said: “The possibility of being infected in New Zealand must be extremely small.”

There were three alternatives, he said.

The traveller had arrived in New Zealand after spending time in the United States on March 18, Bloomfield said at the press conference. They were in the country on a visitor visa.

Baker said if someone had been infected with the virus causing Covid-19, residual bits of the virus could still show up in tests months later, although that was more common if the person had been seriously ill.

The other possibility was the traveller had been infected in transit, and the virus was detected after a short incubation period.

The final alternative to infection in New Zealand, Baker said, was testing error.