Key data guiding critical decision-making on Covid-19 is filled with gaps and even inaccuracies, with detailed information held only at a local level by regional health units.
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It has also emerged there is no central database recording the length of time between a test being taken and the return of a test result.
It means the daily updates of New Zealand's coronavirus cases - 89 yesterday - could be days old with people who have been tested telling the Herald they waited almost a week to get results.
The Herald has been questioning the gaps in information for two weeks and it was only on Friday the Ministry of Health responded, explaining data collection was handled by the 12 regional Public Health Units.
Data management has been an issue in other countries wrestling with the virus with concern in the United Kingdom over inconsistent data and warnings gaps in information may undermine faith in government's response.
The "current cases" list published on the Ministry of Health's website records the date a confirmed or probable case of Covid-19 has been logged, the gender and age group of the individual with the disease, the DHB in which they are located and details of their international travel.
As of Saturday, of the 950 confirmed and probable cases, there were 146 that carry no information as to whether there was international travel. On previous days, a number of those have been listed as "unknown" while others were left blank.
It's not just new cases where information has yet to be obtained. Those without information on whether they travelled overseas - the main route for infection in New Zealand - include two cases from February 28.
Of the 448 cases where it is known there was international travel, only 420 list the country the individual was in before returning to New Zealand.
Other information missing included flight details - just 302 cases of the 448 involving international travel include a flight number.
However, many of the flight numbers listed are not the international flights taken to get to New Zealand but only domestic flights taken after arriving in the country.
Examples include a man aged 20-29 who flew back to New Zealand from Indonesia on March 19 whose only flight details are his journey from Auckland to Palmerston North. In that case, the man's departure date for his journey is listed as April 19 2020 - two weeks in the future. His case is dated April 1.
Other examples include a women aged 40-49 who returned to New Zealand from Egypt on March 9. Her only flight details are her onward journey from Auckland to New Plymouth.
Some flight numbers - such as Beka76 - don't appear to match flight designation numbers for any airline. This was the flight listed alongside a Waikato man aged 50-59 who flew back to New Zealand from United Arab Emirates in mid-March.
Director of Public Health Dr Caroline McElnay said the Ministry of Health information came from the National Notifiable Diseases database, EpiSurv, that held information about confirmed and probable cases of Covid-19, and those under investigation.
It was updated by public health staff in regional public health units in line with notifiable disease law, she said.
"Detailed reporting information can sometimes lag as we need to ensure the accuracy of detail around individual cases.
"Information reported in our stand ups is current - confirmed cases are required to be notified to the Medical Officer of Health at the Public Health Unit and are typically notified with 24 hours of confirmatory testing.
"Details such as flight numbers may be known by the public health units, but not input into EpiSurv."
A spokeswoman for the Ministry of Health - in an earlier statement - said: "Public health units may store other information elsewhere for case management, which is why there may be missing data."
She said the"extensive case interviewing process" can involve more than one interview and could lead to delays inputting information.
The spokeswoman confirmed it did not hold data about the period of time between when an individual was tested and when the test was returned as positive.
"This is managed at a local level."
The Herald has interviewed people who have waited as long as a week for a test result to come back, although it is understood lab work is prioritised towards those most likely to produce a positive result.
It means it is unknown whether the numbers of confirmed and probable cases announced at the daily 1pm emergency briefings are from tests taken inside the last 24 hours or much longer.
The Ministry of Health has listed 81 per cent of cases as linked to international travel or contact with someone who has travelled and 17 per cent as "under investigation". Only 1 per cent of cases are listed as through community transmission.
Professor Shaun Hendy, director of University of Auckland-based research centre Te Pūnaha Matatini, said the quality and timeliness of data had been an issue for his team in its work statistically modelling the behaviour and direction of the virus for the government.
He said the modelling work was intended to give health and political leaders information to assist planning. Good quality, fast data was needed to inform that, he said.
"It has improved this week. A system that wasn't really designed to run at this speed is under stress. It's a big lesson for the health sector in how it manages data."
Hendy said an exercise that incorporated data management and modelling would have helped. And while New Zealand's fragmented health board system hadn't helped in accessing data, he believed a single large bureaucracy would also have struggled.
"We ought to be seeing better data coming through soon. It will give our political leaders better information to make their decisions and for our health system to work more efficiently."
If - as was hoped - the rise in case numbers had reached a plateau, it would help put in place systems to provide even better information. Hendy said Statistics NZ had joined the modelling effort and had been "fantastic".
Health Minister David Clark said the outcome of data collection was contact tracing, which had been successful and was increasing.
"My expectation is that data collection and input is done in a way to achieve what it is supposed to and is refined where necessary."
• Covid19.govt.nz: The Government's official Covid-19 advisory website
They allege the Crown ignored Treaty obligations by not engaging with them.