Updated April 25, 2020 17:10:08

Photo: Broader testing is part of the Government's three-part strategy. (ABC News: Haidarr Jones)

There's a new testing buzzword in Australia and it might sound slightly ominous — sentinel surveillance or sentinel testing.

As our COVID-19 case rates slow, it's part of the next step to staying on top of infection rates in the community and, potentially, easing restrictions.

So does it mean just testing in hot spots? Or targeting at-risk groups?

Here's what the Government is looking at now.

So what is sentinel testing?

If you had a sore throat or fever and went in to get tested, that's passive surveillance (even though it sounds like the opposite).

That's when people possibly sick with COVID-19 go straight to health authorities.

But that misses people who aren't as diligent at monitoring their health or are asymptomatic, which is not great for making sure infection rates stay under control.

Enter more "active" testing, where front-line workers or vulnerable populations might be tested, even without symptoms.

But sentinel testing is more random, as it's trying to see where a virus is moving in the community.

Breaking down the latest news and research to understand how the world is living through an epidemic, this is the ABC's Coronacast podcast.

On Friday, Australia's Chief Medical Officer Brendan Murphy said the Government is still examining exactly what this might look like during the coronavirus pandemic.

He said sentinel situations are "where we sample the population".

But what does this mean?

In regular times (say, when authorities are monitoring influenza), sentinel testing gauges how often a disease is showing up in a community, according to medical virologist Dominic Dwyer, a director at NSW Health Pathology and Westmead Hospital's Institute of Clinical Pathology and Medical Research.

"You try and get an idea of how many people you've tested have the disease," Professor Dwyer said.

"So let's test one in five, or one day a week, just to see what's happening."

But he said exactly what the phrase would mean in relation to COVID-19, or how it would work, is less clear. He said we really want to focus on capturing everyone with symptoms first, so that means making testing even easier to get at pop-up clinics and drive-through testing.

"To me, that's where the money really is."

Photo: Sentinel situations are "where we sample the population", Australia's CMO said. But what might that look like during a pandemic? (Reuters: Vasily Fedosenko)

Prime Minister Scott Morrison told 7.30 last week that sentinel testing "is another level beyond where we are now".

"It's basically trying to work out where outbreaks may occur. And that's how you stay on top of it," he said.

But it will be part of the Government's strategy before Australia potentially eases restrictions: broaden testing, improve tracing and make sure the response is ready if an outbreak happens.

Couldn't we just test hot spots?

Focussing testing in a hot spot, like the Bondi Beach cluster, makes obvious sense and it's certainly what's happening now.

But more random sampling (if and when we can) is important as well, and NHMRC Clinical Trials Centre biostatistics professor Ian Marschner said it's a long-standing statistical technique.

"You don't want to be biased towards testing just in hot spots, you want to spread that out over a range of different geographical areas," he said.

As Australians see more days with low (or even no) new coronavirus cases in each state, keeping an eye on early infections is going to be crucial.

Find out more

Professor Marschner said that infection data is made up of both the incidence (the rate of new infections) and prevalence (how many there are in the community).

"Both of those measures are important in an epidemic," he said.

"Having tools in place that allow us to very quickly monitor changes in infection rates and infection prevalence is really what we need at the moment.

"If we do start to wind back the restrictions, then we're in a place to respond very quickly if there is a resurgence in infections."

And he said getting a handle on infection rates is important.

"It's not actually the trends in cases that are the important thing, it's the trends in infection rates," he said.

That's because infections come first, sometimes days or weeks before a case is formally identified.

He said even though infection rates are harder to pin down: "We should be trying to do analytical techniques that at least allow us to investigate what's going on."

Can more testing all around help ease restrictions?

Good social distancing has helped to keep Australia's coronavirus curve in OK shape.

But Mr Morrison and the National Cabinet have been clear that, before restrictions are lifted, the right tools to jump on any outbreaks must be ready.

Infographic: Growth in known cases in key countries, on a logarithmic scale

This chart uses a logarithmic scale to highlight coronavirus growth rates. Read our explainer to understand what that means — and what we can learn from countries that have slowed the spread.

On Friday, the PM said Australia was now in the "third wave" of the virus — the community transmission phase — where the origin of cases is sometimes harder to pin down.

"That requires particularly different tools, building on the ones that we already have in place. And that is the testing, that is the tracing, and that is the rapid response," he said.

"We should be aware, as a community right across the country, that when we take further steps to ease restrictions, of course, we will continue to see outbreaks.

"What matters is being able to move on them quickly."

And on Friday, testing criteria was expanded across Australia to all people with mild symptoms, indicating more testing generally is on the cards.

"Anybody with acute respiratory symptoms — cough, sore throat, runny nose, cold symptoms, flu-like symptoms — can get tested," Professor Murphy said.

"This will significantly expand the population of people tested."

Topics: covid-19, respiratory-diseases, epidemics-and-pandemics, australia

First posted April 25, 2020 17:08:22