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The Ministry of Health earlier today said the person's case was under investigation, but serology tests run today have shown the presence of antibodies that further confirm this is a historical infection.
A PCR test conducted today had also returned a negative result.
The person arrived from the US and went through 14 days in an Auckland managed isolation facility - where they returned two negative tests and were asymptomatic - before leaving on 21 September.
This week, the person sought medical care after feeling unwell and a subsquent test for Covid-19 returned a weak positive result.
An acute non-Covid-19 respiratory illness can sometimes create a situation where residual Covid-19 virus particles are detected when a sample is taken.
However, the ministry says there is no risk to the public and international research shows people with a historical Covid-19 infection are not infectious.
As a result, the ministry says no further management of close or casual contacts is required.
The ministry today also revealed there are four new cases of Covid-19 in managed isolation.
The first imported case arrived from the Philippines via Hong Kong on October 3 and was taken to a managed isolation facility in Auckland.
They tested positive as part of routine day 12 testing and have been transferred to the Auckland quarantine facility.
The second imported case arrived from Peru via Mexico and the USA on October 10 and was taken to a managed isolation facility in Christchurch.
They tested positive as part of routine day 3 testing.
The third and fourth imported cases both arrived from Hong Kong on October 11 and were taken to a managed isolation facility in Auckland. They tested positive as part of routine day 3 testing and have been transferred to the Auckland quarantine facility.
The total number of active cases was 46 – all imported cases. There were no active community cases of Covid-19.
Further details about the suspected historical case under investigation are expected to be released later today.
Yesterday laboratories processed 5078 tests, bringing the total number of tests completed to date to 1,021,931.
- additional reporting NZ Herald