Why new sub-cluster has officials on orange alert

Analysis: The discovery of a sub-cluster of infections related to a "bereavement event" could extend the long tail of the Auckland cold store cluster, Marc Daalder reports

Director-General of Health Ashley Bloomfield has said officials are on "orange" alert after the discovery of a new "sub-cluster" of Covid-19 cases in Auckland.

The new grouping of cases has been traced back to a "bereavement event" attended by someone in the Mount Roskill church mini-cluster and a subsequent funeral and is associated 14 cases. Among these are a student at St Dominic's Catholic College and a bus driver on the Northern Expressway route.

What does this new sub-cluster of a mini-cluster mean for our response?

To begin with, it's the first time we've seen more than a handful of community cases spreading in a Level 2 environment. While the health system has prepared for this scenario by boosting contact tracing and testing capabilities, this will put those to the real-life test.

"The two fundamental parts of that will be the testing - and we know our system's got good capacity to test. Wide testing, wider than we might otherwise do," Bloomfield said. This includes the testing of casual contacts - those who might have briefly shared a bus or a shop space with a confirmed case but didn't meet the rather strict criteria (being within 1.5 meters of someone for more than 15 minutes) to be classified as a close contact. Earlier in the pandemic, only close contacts were tested.

"Secondly, having that contact tracing capacity stood up and that ability to bring in the Public Health Unit people from around the country. The mainstay will continue to be testing, isolation, support for isolation including the use of managed isolation facilities and the quarantine facility in Auckland, and of course the rapid isolation contact tracing."

What officials will be looking to do is make sure that the newest small outbreak has been ring-fenced, with all cases and close contacts identified and isolated. The sub-cluster has been caught much earlier than its parent church cluster, which could make this easier.

Although the first potential infection event in the Mount Roskill church cluster occurred on August 7, officials didn't identify it until nearly three weeks later. This time, the index event was a September 2 visit by members of the church cluster to the home of a bereaved person. The virus was then transmitted through a funeral and outwards to infect a total of 14 people by 9am on Wednesday.

Still, that it was announced just a week after the originating event indicates officials have a solid chance to stop further transmission. The incubation period for Covid-19 - the time between being infected and being able to infect others - is thought to be between five and six days on average. That means there's a good chance the people infected on September 2 have infected others, but that second generation is less likely to have transmitted the virus any further.

All 108 close contacts of the 14 cases have been contacted and are self-isolating, Bloomfield said. If officials are quick enough, they can identify any other instances of transmission and isolate those too, stopping the sub-cluster from swelling in size like the church cluster has. Out of the 171 community cases in the second outbreak, at least 43 of them have been linked to that church cluster.

If the sub-cluster isn't isolated quickly enough, however, we could see a repeat of the church cluster. Of the 22 community cases reported over the past week, just three have been linked to the main cold store cluster, meaning that has largely been isolated. But the long delay between the start of the church cluster and its identification has meant the virus was able to transmit over several incubation periods and officials are still finding new cases.

One of these new cases was a close contact of another case. They had been tested but went to the household of the bereaved person and kicked off this sub-cluster. The hope is that the same won't have been repeated by members of this new sub-cluster at other social or work events, unaware that they had been infected at the funeral.

If it has been, that could extend the much discussed "long tail" of the outbreak a little longer and further delay a move down the alert levels for Auckland or even the rest of the country.

Bloomfield was candid when asked what colour his metaphorical dashboard was, admitting the sub-cluster was "raising some flags".

"It's flashing orange and it won't flash or go steady green until we're really confident we've got this outbreak well-circled. I should say that this grouping here that's appeared around this bereavement is the only additional tentacle out from the Mount Roskill grouping and there are no other ones that have emerged either over the last week or so," he said.

The hope is that it stays that way.

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