The number of Covid-19 testing stations across New Zealand has increased to 120 as the Government continues to ramp up its daily test count. By the end of the week, Health Minister David Clark said he expects New Zealand to have completed 60,000 Covid-19 tests. That's up from nearly 47,000 tests carried out so far. Epidemiologists are optimistic that New Zealand's case rates are tracking where they should be at this stage of the lockdown, but what comes next for our testing regime – and is it possible we're still missing a large number of carriers? Science reporter Jamie Morton asked Dr Amanda Kvalsvig, a senior research fellow at Otago University's Department of Public Health.
How is our testing regime going?
In just a few weeks, Covid-19 surveillance has had to sprint from a standing start to a point where thousands of tests are being done every day.
The information we get from testing is vital. Each positive test is an opportunity to stop onward spread of the virus by isolating the case and tracing their contacts.
And by putting together test results around the country, we can track the progress of the pandemic and direct action to where it's needed.
But Covid-19 surveillance is about much more than counting cases. To make a safe decision about when to exit lockdown, we need to know not just who is being counted, but who isn't.
We need a pandemic response that uses common-sense approaches, such as ensuring that community-based assessment centres are accessible for anyone who needs them.
We also need a cohesive and innovative 21st century approach to tracking Covid-19.
This means developing a system that collates multiple available data sources to pick up signals about illness in communities, physical distancing and other indicators of outbreak risk.
This information must be used sensitively and appropriately to guide critical decisions for public health.
Is it possible we could still be missing a large number of silent carriers who are not asymptomatic - or who, for some other reason, aren't being tested or can't access testing?
No system could capture every single case, but we don't have to identify 100 per cent of cases to stop the pandemic.
The key point is being able to identify enough cases to find and stop transmission chains.
By definition we don't know how many unknown cases there are, but there are statistical and epidemiological methods we can use to make an estimate.
Those calculations will be helpful for making decisions about appropriate testing strategy, including how to find more of these missed cases, and how many tests are needed for a safe level of pandemic control.
In a recent blog, yourself and Otago colleagues suggest testing of symptomatic people could be expanded in a "step-wise manner" to help toward the goal of elimination. How could this happen?
Expanded testing will need to be systematic, prioritising approaches that can find the most cases and then working down the list.
A major deciding factor will be knowledge about our populations and who might be most at risk, but the practicalities of testing in different settings will also be an important consideration.
Whatever the approach, it has to work on the ground.
What potential insights could expanding testing give us about factors like demographics or symptom profiles?
The known symptom profile of a disease is strongly shaped by how and where cases are identified.
Expanded testing for Covid-19 in community settings will tend to identify cases with milder symptoms, but the profile will still be strongly influenced by the guidelines about who gets tested.
Only when we have a test of immunity after infection - and apply it widely in the population - will we be able to look back and see the full spectrum.
That spectrum might include many people who were unaware of being unwell at the time, and we might also get a better idea of unusual symptoms that aren't being recognised at the moment.
You and colleagues also suggested we could be updating our aggregated daily testing results as Iceland does. How does that country's system work and why might it be a good model for us?
Our Ministry of Health is providing daily results on their website, but Iceland's dashboard approach is a particularly good example of health communication - it's user-friendly and clear.
Everyone in Aotearoa New Zealand has a role to play in stopping the pandemic, so good quality, timely communication is vital.
A third stage could be testing people who are have no symptoms, but have a higher level of risk - like those working in supermarkets, for instance. What are the benefits here?
We're seeing conflicting results from other countries about the risk of viral spread from people without symptoms, either because they're in an early stage of infection, or because they have the infection but never feel unwell.
In time, this aspect will become better understood but the evidence so far suggests that to stop the pandemic, our testing efforts and resources are better focused on people with symptoms.
However if that evidence changes, people who have high levels of contact with the general public would certainly be a good place to start that type of testing.
There's also a suggestion of "mop-up" testing to ensure that elimination has been achieved. What might this like and how might be achieved, and at what scale? What part might testing wastewater play here?
With infectious diseases testing there is always a trade-off between public health resources and public health benefit.
The balance is delicate and it shifts depending on how common the disease is in the population.
We're testing widely for active infection at this intense phase of elimination. Once the numbers go down the approach will change.
In some ways it's likely to be more focused, for example to ensure that no new infections are arriving at our borders.
In other ways it could become more broadly population-based, such as testing randomly selected people for immunity to the virus once a test becomes available.
Testing wastewater is a very interesting possibility because it's relatively low-cost and and doesn't require people to present themselves for testing.
It could be a useful way of monitoring Covid-19 in the long term – and it is clear that there will be a long term. This virus will be with us for a long time yet.