Covid-19: What is an “unlinked subcluster”? Need to worry about them?

explainer: As the number of daily Covid-19 cases in the community continues to decline, 11 new cases announced on Friday – The focus is on when Auckland will break out of the alert level 4 blockade.

The case number is the protagonist of the show. But there are other important means of tracking.

The occurrence does not have to be zero to control the occurrence.

For example, a positive Covid-19 test can infect other people in the family. Their positive test results are irrelevant to public health authorities if all of us are quarantined while infected.

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But if someone in town is positive on the test and they aren’t in contact with anyone in my family, that’s a problem. Contact tracers try to plot the route of infection and identify other potential cases in the process.

I’ve heard a little So-called mystery case.. These are cases that are not yet epidemiologically associated with the current outbreak. On Friday, there were 29 such cases still under investigation.

I have also heard about Linked subcluster, Or a group of cases involved in the outbreak.

But on Sunday, there was a new number given as part of the Ministry of Health’s daily update: the number of epidemiologically unlinked subclusters. There were six of these. By Tuesday, there were nine people.

Like mystery cases, these are group Percentage of people who test positive for Covid-19 and are not yet associated with a widespread epidemic.

The ministry told me that all unlinked subclusters have contained infections in the last two weeks. A total of 101 cases are related.

How do you connect people with the Covid-19 epidemic?

In January 2020, scientists published the genome of SARS-CoV-2, the virus that causes Covid-19. NS genome A complete set of biological genetic material.

All viruses are constantly evolving and changing.. Especially when they are as mobile as the coronavirus. Currently, there are thousands of unique SARS-CoV-2 genomes.

We can witness this evolution thanks to gene sequencing technology that analyzes virus samples from positive cases and compares them to other cases.

Genomics tells us that the two cases are linked, but we don’t know how they are linked.Layering Genome findings In addition to other epidemiological information, public health authorities can know if a new patient has caught the virus from a known source and can work to identify the point of infection.

In a situation where one person, perhaps called a “superspreader,” infects many others, the genomic data for all positive cases are very similar.

On the other hand, if the virus jumps from person to person and from person to person, the strain is more likely to mutate. It’s like gossip – The more the story spreads, the more mistakes sneak up on the story.

Therefore, a cluster is a group of people who are likely to get sick with each other.

Outbreaks, clusters, and subclusters

The outbreak in Auckland is related to a New Zealander border incident that returned from Sydney on a controlled Red Zone flight and was tested positive for the delta variant of the virus on August 9.

On August 17, at the age of 58, living on Auckland’s North Shore, later called Case A, a positive virus test triggered a national alert level 4 blockade.

It is not yet known how the virus spread to the community. However, we know that community cases so far have been associated with returnees in Sydney. This means that as of Friday, 879 outbreaks are in a single cluster.

Within that cluster, the Ministry of Health has identified sub-clusters. Eight are linked and nine are unlinked.

The largest linked sub-cluster with 374 cases is associated with the divine rally of the Samoa Church in Manguere, South Auckland. This service, a joint rally of more than 500 people, took place on August 15, involving several other churches.

The second largest is the Birkdale Social Group, which has 76 cases. This group includes Case A and other nose shore contacts.

Both of these sub-clusters have not grown significantly since last week, suggesting that the virus has spread throughout the connected households and no further.

The other six linked subclusters are not named by the ministry for privacy reasons and therefore appear as subclusters C, D, E, F, G, and H in the graphic. We know that one of these subclusters has the following link: Auckland University of Technology (AUT), and another university, was formerly known as “Massie’s Home and Workplace.”

What do you know about the nine unlinked subclusters?

“We know that they are genomically related to the development of the current community, but these clusters are not yet associated with known exposure events or cases,” a ministry spokesman said. Told me.

A subcluster can contain up to two people. Currently, the smallest subcluster contains four linked cases. Most unlinked subclusters contain less than 20 people.

Professor Michael Planck of Mathematics states that unlinked subclusters represent missing links somewhere in the transmission chain, and that there may be cases that have not yet been discovered. Suggests.

“The fact that the subclusters are small isn’t really reassuring in this regard, because what’s more worrisome than what we know is the cases that may have been overlooked.”

Shaun Hendy, a Covid-19 modeler and professor of physics, states that genomics provides an indication of how these subclusters relate to other subclusters.

“But ideally, we need to be able to track epidemiological links and eliminate the possibility of other undiscovered clusters that may have been generated by that link.”

This is why it is so important to have a test if you have symptoms, he adds.

What does all this uncertainty mean for alert levels?

Unfortunately, unlinked subclusters and mystery cases prevent the government from confidently lowering alert levels without compromising the goal of removing Covid-19 from the community.

Expert agrees The lack of links could mean the difference between Auckland remaining a Level 4 blockade and moving to Level 3 next week.

University of Otago epidemiologist Michael Baker Advise government on Covid-19Said that we need days with no unlinked cases Before the area leaves the blockade.

“As long as there are people out there who can infect others, that’s a problem.”

On Friday, Health Director Ashley Bloomfield told reporters over the past four days that an average of 9,000 people were tested for Covid-19 per day.

He said essential workers and surveillance tests on pop-up sites would hopefully find cases that were missed.

“We now have a case [outbreak’s] The tail, and we must work to detect if they are further undetected flags for community communication. “

The Cabinet will consider pandemic regulation in Auckland on Monday.