The Ministry of Health is investigating a suspected historical case of COVID-19 in a crew member who is docked at the Port of Tauranga.
The person returned a weak positive test with a high CT value, which the ministry says "indicated an old infection".
"It appears most likely that this crew member had COVID-19 some time ago and is no longer infectious. The IVS Merlion arrived into New Zealand waters on October 15 after departing Indonesia on September 24," the Ministry of Health said.
The ship is still docked in Tauranga.
"This infection has not been passed on to any other crew member - they have all tested negative and have been on board the vessel for three weeks."
It adds no crew members have come ashore, so there is a "very low risk" of transmission to New Zealanders.
"As a precautionary approach, the case under investigation has been isolated and has had a repeat COVID-19 test as well as a blood test. The results of these tests will confirm whether they are a historic case."
All crew members are being treated as close contacts until the case investigation is complete. No crew are allowed to leave the vessel until this investigation has finished.
"The health staff and other port staff, who had minimal contact with the crew, have all been informed and no further action is deemed necessary," the Ministry of Health said.
It follows an employee of a company that works on-board vessels at the Ports of Auckland, but is not a Ports of Auckland staffer or contractor, testing positive for COVID-19 during the weekend.
Earlier on Monday, during the daily COVID-19 announcement, Director-General of Health Dr Ashley Bloomfield said it was "particularly pleasing" there were no new cases in the community following this port worker's confirmed infection.
Genome sequencing revealed the man's infection is not of a type that's yet been seen in New Zealand, confirming it's not linked to the country's recent second outbreak.
The source of the man's infection is still being investigated, but Dr Bloomfield said the ministry believes he was likely infected while working on a ship in Auckland called the Sofrana Surville on October 12 and 13.
The nature of his work means he boards ships that have travelled from overseas and have international crew members.
The Sofrana Surville had travelled from Brisbane, Australia to Tauranga and then on to Auckland. Upon docking in Auckland, eight crew from the Philippines came onboard on October 13, while four others crew members left and flew home.
The Sofrana Surville has since been to Nouméa, New Caledonia and is now en route back to Brisbane. The ministry is in contact with health authorities across the Tasman and will be notified of test results once the ship docks in Australia.
As part of its investigation, the ministry is now carrying out testing on crew members of another ship that the case worked on prior to his time on the Sofrana Surville.
The ministry does not believe this ship is the source of the infection, as it only operates in New Zealand, but is undertaking testing as a precaution.
