Covid 19 Omicron outbreak: Analysis - Covid death reporting explained

In July Dr Ashley Bloomfield announced the focus of New Zealand's Covid-19 death reporting was moving to deaths from Covid-19. Photo / Mark Mitchell

ANALYSIS:

The NZME newsroom's head of data Chris Knox, who recently returned to NZME after working in the Ministry of Health's Covid-19 data team, explains Covid-19 death reporting.

Covid-19 has become a leading cause of death in New Zealand, but the seemingly simple question "How many people have died of Covid-19?" doesn't have a simple answer.

''What the numbers mean, where they come from and why there can't be just one total?'' are regularly asked questions, and they're good questions. This explainer will help answer some of them.

Under normal circumstances, 'cause of death' is determined soon after death and recorded on a death certificate. However, that record isn't suitable for counting deaths until it is translated into the World Health Organisation's International Statistical Classification of Diseases (ICD-10) coding. This usually happens within a few months.

When a death is referred to the coroner – around 10 per cent of the time – an official cause of death decision may take a few years.

Waiting months or years for information on Covid-19 deaths is clearly unacceptable – there would be no way to know in the short term what the situation looks like.

So New Zealand reports Covid-19 deaths using two separate but overlapping categories: the number of people who have died with Covid-19 and the number of people who have died of Covid-19.

Deaths of Covid-19 is the key number, but "deaths with" is valuable either when cause-of-death data is very incomplete or as an estimate of how incomplete cause of death data is.

Deaths with Covid-19 can be readily identified without clinical input, so these can be reported on quickly and relatively easily.

New Zealand, following the UK, defines a death with Covid-19 as any death that occurs within 28 days of being reported as a Covid-19 case.

Other countries, like the US, do not report on deaths with Covid-19 at all.

A hypothetical unlucky individual who was struck by lightning and killed right after reporting their positive RAT test would be reported as a death with Covid-19.

All deaths are included in the deaths with Covid-19 count regardless of the cause of death – even if they are our unlucky lightning victim – because adding any requirement to understand cause of death before reporting on deaths with Covid-19 would slow the reporting process.

Interestingly, while in New Zealand deaths with Covid-19 is a larger number than deaths from Covid-19, in the UK more deaths from Covid-19 have been identified than deaths with.

Initially, our reporting focused on deaths with Covid-19 as cause of death data was very incomplete.

The Ministry of Health created an expedited system to code the cause of death of most deaths with Covid-19 within a few days – much faster than the usual process that generally took a few months.

And in the early stages of the omicron outbreak, individual Covid-19 deaths were reported and acknowledged more quickly than any cause-of-death classification process could ever actually allow.

In July the focus of New Zealand's Covid-19 death reporting moved to deaths from Covid-19.

New Zealand, following both the UK and the US, defines deaths from Covid-19 as deaths where Covid-19 is listed as a cause of death on the death certificate – the Ministry of Health refers to this as 'Covid-19 attributed deaths'.

The number of Covid-19 attributed deaths - 1815 as of August 19 - is now the primary Covid-19 deaths statistic New Zealand reports.

This still is not a complete accounting of Covid-19 deaths. At the time of writing, 258 deaths of people who died with Covid-19 have not been classified. Many of these deaths have been referred to the coroner and may not be resolved for a year or two.

Covid-19 attributed deaths (deaths from) contains two more detailed categories: deaths where Covid-19 was the underlying (or primary) cause of death and deaths where Covid-19 was a contributory cause of death. Sixty-five per cent of Covid-19 attributed deaths had Covid-19 as the underlying cause.

An example of a death where Covid-19 was a contributory cause of death would be someone who died of cancer but Covid-19 caused them to die more quickly than if they hadn't caught Covid-19.

Once all Covid-19 deaths have been classified – for current deaths this will not be until the end of either 2024 or 2025 – counting deaths with Covid-19 no longer serves a purpose and we will finally have only one total: Covid-19 attributed deaths.

Although "Deaths from" is now the primary number used, when the Ministry announces the number of deaths reported in the last 24 hours these deaths are deaths with Covid-19 as 24 hours isn't enough time for cause of death classification to be completed – especially during the weekend.

The number of deaths with Covid-19 that have been classified as 'Not Covid' is also reported. This would include our hypothetical unlucky lightning victim and lets us know how much of an over count 'deaths with' reporting was. Currently, 21 per cent of reported deaths with Covid-19 had nothing to do with Covid-19.