There are no new cases of Covid-19 in New Zealand today, the Ministry of Health has confirmed.
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Three people are in hospital with Covid-19, one each in Middle, North Shore and Auckland City hospitals.
There are 39 people isolating in the Auckland quarantine facility from the community, which includes 18 people who have tested positive for the virus and their household contacts.
One previously reported case is now considered to have recovered, bringing the total number of active cases to 61; of those, 29 are imported cases in managed isolation and quarantine facilities, and 32 are community cases.
The total number of confirmed cases remains at 1464.
There have now been a total of 917,699 Covid-19 tests processed.
Director-General of Health Ashley Bloomfield says it's important we all remain vigilant, monitoring our health and not going out if symptoms appear.
There have been instances of people who have recovered from Covid-19, but with later test results coming back positive with a high CT (cycle threshold) count - which is considered to be a weak positive result, he says.
Dr Bloomfield says these historical cases are not infectious.
He says sometimes people with historical infections seek a test because they have a respiratory illness and it seems an acute non-Covid respiratory illness then creates the conditions where if there's residual Covid-19 virus or viral fragments inside someone's nasopharynx then that is detected and the results come back positive.
Over the past two months, the ministry has seen this cover four groups of people, including those who tested positive overseas after departing from New Zealand.
The second group are people who arrive into New Zealand and who return a positive test in managed isolation - or subsequent to leaving managed isolation after testing negative during their period there - without acute symptoms.
A third group are people who have been in the country throughout the pandemic who return a positive PCR result and who had a documented infection earlier in the year, and are already in the case count.
The last group is of also of people who have been here throughout the pandemic and returned a positive PCR result, but did not have a documented infection earlier in the year, so they are not in the case count.
"These people have a clear history of a previous acute illness consistent with Covid-19 but were not tested at the time, and follow-up serology testing confirms that they (and possibly other members of their family) have been infected in the past with Covid-19," the ministry said in a statement.
Dr Bloomfield says the ministry is developing a protocol and setting up a panel to standardise how these cases are managed and reported.
He says the key thing about the testing plan is that anyone anywhere in the country with symptoms should be tested.
The panel and protocol will help ensure a consistent approach to cases that are effectively borderline cases and that are being further investigated, he says.
The panel will confirm whether the infection is historical or recent and to guide public health measures, especially regarding contact tracing and management.
The ministry says historic cases under investigation will be included in the total number of cases in the future, if it is confirmed that they were infected and were not added to the tally.
Update on returnee's case and flight
The person who tested positive after leaving an isolation facility in Christchurch and who travelled via a plane to Auckland, had 85 close contacts on the charter flight.
So far 29 have been tested - the people in the front nine rows of the plane. All but one have returned a negative test. The remaining person returned a positive test with a high CT value yesterday - suggesting an old infection.
The person returned a negative test this morning and has not had symptoms since their arrival into the country.
Serology testing is also being undertaken, Dr Bloomfield says.
The person returned negative day 3 and 12 tests in isolation. This case remains under investigation, with the ministry wanting to confirm whether this is an historic case, and whether it has already been reported as a case in India.
Meanwhile, a precautionary approach is being taken and the person has been transferred to the Auckland quarantine facility.
Dr Bloomfield says mobile testing sites will be used to test non-symptomatic people in high-risk industries like hospitality workers who may come in contact with Aucklanders.
He says his team is looking at whether to test people after they've left managed isolation.
It's rare for an incubation period to be longer than 14 days, but it's not unheard of, he says.
Auckland has operated at tailor-made "alert level 2.5" since 31 August. The city will move down to level 2, with eased restrictions on gatherings, at 11.59pm on Wednesday.
That level will be in place for 14 days, with Cabinet set to review those settings again on 5 October.
The rest of the country has moved down to alert level 1 today but there is still a risk of Covid-19 returning to the community, according to the Ministry of Health.