Air New Zealand says it's possible a crew member who tested positive for Covid-19 in Shanghai may have contracted it while in the Chinese city a week earlier.
The cabin crew member tested positive in during screening at Shanghai's Pudong Airport on November 22 after testing negative in a pre-flight test in this country four days earlier.
The positive test was confirmed on their return to New Zealand, but the infection can't be linked to any case in this country.
The airline's chief medical officer Ben Johnston said Auckland Regional Public Health and the Ministry of Health were leading the investigation.
"They are looking towards a previous trip the crew member had made to Shanghai," he said.
Earlier this week, two positive cases among cargo workers at Pudong reportedly threw the airport into chaos when it was put in a lockdown as 18,000 staff were tested.
Johnston said requirements for air crew were very strict in Shanghai, where Air New Zealand is maintaining a skeleton service.
Staff are escorted off the aircraft, given a Covid test and then taken to a state-run quarantine hotel where they are kept in their rooms. Food is delivered to their doors. He said they were followed by health staff, who sprayed disinfectant where they had been.
"We're aware of some cases in the cargo operations around Shanghai airport but not in areas our air crew would have been to. That is an open line of investigation."
China is not considered a "higher-risk" country for the airline, where stringent rules apply to returning crew.
The United States is gazetted as higher risk and Air New Zealand flies to Los Angeles and San Francisco. The airline said today the Covid-positive crew member hadn't flown there recently.
Johnston said it was possible the source of the infection might never be known, as in the case of the August cluster that stemmed from cases at Americold in Auckland.
"Sometimes this happens."
There were some passengers on the flight, but he did not know how many.
He said Air New Zealand crew had been free of Covid for seven and a half months, which showed how "incredibly" careful staff had been.
He said no other Air New Zealand crew in quarantine or in managed isolation or isolating at home had tested positive for Covid since the positive test early this week.
The airline and health authorities were reviewing prevention measures while on flights and layovers overseas as well any restrictions when crew return. Johnston said the crew member had followed all the rules.
All crew were doing well, he said.
Crew could get pre-flight tested at GPs, community testing centres and at an airline facility at Auckland Airport where testing is done according to public health guidelines and sent to the same labs that all others are.
The Ministry of Health has said while genome sequencing had showed they likely caught the virus overseas, it was still not known when or where.
Today it said 17 close contacts of the crew member had now been identified. Eleven had tested negative, and the results of six people's tests were pending.
The ministry requires New Zealand-based air crew overseas to follow a long list of conditions including:
• Wearing personal protective equipment at all times (to the greatest extent practicable) while working in a role involving direct interaction with aircraft passengers or while in any place other than on an aircraft or in their room (or a fellow crew member's room) at the accommodation where the aircrew member is staying.
• Maintain physical distancing of 2m or more from all people (to the greatest extent practicable) other than people on an aircraft on which the crew member is working or fellow crew members.
• Travel as directly to any accommodation at which they are staying.
• Meet the self-isolation standards at accommodation until they are required to travel from it.
• Meet the overseas airside condition after arriving in a country outside New Zealand including if not staying in any accommodation before departing the country or staying in any accommodation on the airside of an airport before departing the country.
New rules for returning crew were put in place last month including the requirement for those returning from high-risk locations (the US) were required to self-isolate for at least 48 hours after they return and until they have received a negative test.
Extra weekly surveillance testing for some lower-risk New Zealand-based international air crew was also introduced.