The Wellington SCL laboratory at Wellington Regional Hospital. Photo by Elias Rodriguez/Getty Images
The Wellington SCL laboratory at Wellington Regional Hospital. Photo by Elias Rodriguez/Getty Images

SocietyJune 25, 2020

Siouxsie Wiles: Why I’m confident there is no community transmission in NZ

The Wellington SCL laboratory at Wellington Regional Hospital. Photo by Elias Rodriguez/Getty Images
The Wellington SCL laboratory at Wellington Regional Hospital. Photo by Elias Rodriguez/Getty Images

Mistakes in the testing regime for people departing managed isolation have prompted alarm about the possibility the virus has been seeded locally. Dr Siouxsie Wiles offers a dose of perspective, and explains why the critical line of defence remains the isolation and quarantine process.

Both the leader of the opposition Todd Muller and University of Auckland Professor Des Gorman have gone on the record as saying they suspect Covid-19 is spreading in the community in New Zealand once again. Let me explain why I don’t agree with them.

As best I can tell there are two reasons Muller and Gorman have jumped to the conclusion they have. The first is that we’ve been told that more than 2,000 people may have left their 14 days of managed isolation between June 9 and 16 without being tested for Covid-19 as they should have been. The second is that over that same period more than 50 people left managed isolation before their 14 days were up on a compassionate exemption. Again, mostly without being first tested.

Before I get into the nitty-gritty, it’s worth noting that we’ve had more than 20,000 people go through managed isolation since the beginning of April. Almost all of those would have left without being tested. There is no evidence any of those people have transmitted the virus to anyone in the wider New Zealand community. On top of that, in the last week or so more than 45,000 tests have been processed and the only positives have come from people in managed isolation facilities at the border.

Fourteen days in managed isolation is our first line of border defence, not testing

Because of what we now know about how this virus infects people, lots of countries have settled on 14 days as the time at which if someone doesn’t show symptoms of Covid-19 then it is highly unlikely they will have the virus and be infectious. In other words, they are at very low risk of transmitting the virus to others or “seeding” the virus back into the community. We have been using this 14-day isolation period for several months. This is our first line of defence.

We also have two different types of isolation here. Managed isolation and quarantine. Quarantine is for those people who either have symptoms when they arrive in New Zealand or who develop symptoms/test positive during their fortnight of isolation. Everyone else is in managed isolation. This is a very sensible precaution as it keeps people who are at a higher risk of being infectious separate from those who may not be infected at all.

Until June 9 we weren’t routinely testing people in managed isolation for Covid-19 unless they developed symptoms. We weren’t the only country who took this approach. Now we’ve added two tests: one around day three and the other around day 12 as an extra precaution. More about those tests shortly.

As for the more than 2,000 people who left managed isolation between June 9 and 16 without being tested as they should have been? They left after their 14-day isolation just as people were doing before June 9. Yes, we don’t have that extra layer of precaution of a negative test result, but they had completed their two-week isolation. That is the most important thing.

Compassionate exemptions

Of higher risk to us are those people who were given an exemption to leave managed isolation on compassionate grounds before their 14 days were up. Between June 9 and 16 there were 54 people who did this. It’s worth noting that there were strict rules around their being able to leave. They were going to either self-isolate at home or with family, or had permission to visit a dying relative, attend a funeral, or grieve with family before returning to managed isolation. They were under strict instructions not to go to supermarkets or shops and were supposed to wear PPE – personal protective equipment – in case they were infectious.

The risk of transmission from these people is obviously higher because they were within the 14-day window and so could have been infectious. But the risk was to the people they were spending large amounts of time in close contact with. That’s why they were required to wear PPE – to minimise that risk as much as possible.

What does a positive or negative Covid-19 test actually mean?

The test we use here in New Zealand detects the presence of the virus’s genetic material.

A positive test means that the virus has been detected. It doesn’t tell us whether the virus detected is viable and infectious or whether it has been destroyed by our immune system. There is plenty of good evidence that people can test positive for the virus several weeks after they have recovered from the infection and are no longer infectious. We also know that some people can test positive for the virus and never have any symptoms. These people are often referred to as asymptomatic and there is very little evidence that they are very infectious. One really excellent study from Taiwan found no onward transmission of the virus from the asymptomatic people they followed. I wrote about that – and why we need more studies like this – here.

A negative test can also mean one of several things. It can mean what we want it to mean – that the person doesn’t have the virus – but it can also mean the swab didn’t get enough virus to detect. That’s why we’ve taken a very conservative approach when dealing with symptomatic people who tested negative but had all the other signs that they could have Covid-19 – we counted them as probable cases. A negative test could also mean someone is in the incubation period. That’s why having two tests is useful. It’ll give us a better chance of picking any false-negatives from failed swabs or any people who were incubating the virus when they were first tested. It’s also why testing at day three of isolation is more useful to us than testing people when they first arrive in New Zealand.

So, what will the day three and day 12 tests tell us? Well, the main thing they will do is allow us to pick up people who we would have missed before because they didn’t have symptoms. That could be because they are infected but asymptomatic or because they had had an infection in the weeks before they arrived but since recovered. There is a real lack of data on people who are truly asymptomatic so the fact we will now be capturing them too will be very useful in helping our understanding of this virus.

What about the small number of people who won’t be tested?

The Ministry of Health recently said that there are 11 people who have left managed isolation who they won’t be trying to test. They said that is either on the basis of health, because they are a child, or because they have left the country.

That statement made an important point. Yes, the rule is that everyone will need to be tested before they leave managed isolation, but the reality is that a small number of people won’t be, and that’s not because they’re “slipping through the net”. It’s because there may be a genuine health reason why it’s not a good idea to test them, or because they are children.

Depending on the age of the child, getting a test can be quite distressing. It can also be tricky to get a useful sample from a child who doesn’t want a swab stuck up their nose. Does that mean that an infectious child is going to sneak past our defences? No. I’ve written before about the enigma of children and Covid-19. All the evidence to date points to children being less likely to be the source of infection, including a new study of primary school children in France. They found children mainly caught the virus from their parents and that there was no onward transmission from those children to others in their schools.

We’re in this for the long haul

We need to remember that we are in this for the long haul. We’re approaching 10 million confirmed cases of Covid-19 around the world. That number is only going to rise. New Zealand is one of a few countries around the world where it is safe to see friends and family, go to work, and go to the shops or a restaurant. New Zealanders have every right to come home, provided they do their 14 days of managed isolation.

But people are people and mistakes can happen. That’s why the rest of us need to keep calm and stay vigilant. If you have any symptoms that could be Covid-19, call Healthline or contact your GP immediately. Unfortunately, our lockdown didn’t eliminate the common cold so it’s likely many of us will need a test as winter drags on. But while the controls at the border are our first line of defence, the testing the rest of us is our second line of defence. Together, with all the improvements to our contact tracing system, these measures will keep us safe.

Keep going!