So does the official COVID-19 count represent the actual number of cases in Australia? No, said UNSW Professor Raina MacIntyre, the head of the Biosecurity Program at Kirby Institute. “I am absolutely certain there are undocumented cases in the community, some who might think they have a cold, some with no symptoms, who are out there spreading infection,” Professor MacIntyre said. Professor MacIntrye said we could now be in the silent growth phase of an epidemic that would be realised only when the health system was overloaded. She said this was what happened in the United States, where it was likely that asymptomatic spread of COVID-19 drove the silent growth phase in that country.

“Ample research shows anywhere between 34 to 50 per cent of all infections are asymptomatic,” Professor MacIntyre said. Loading Replay Replay video Play video Play video Who are we testing now in Australia? Paul Komesaroff, a Professor of Medicine at Monash University, said the World Health Organisation had often repeated that the answer to the COVID-19 epidemic was “testing, testing, testing”. The Australian government Department of Health’s website, however, said you would be tested only if:

You have returned from overseas in the past 14 days and you develop respiratory illness with or without fever

You have been in close contact with a confirmed COVID-19 case in the past 14 days and you develop respiratory illness with or without fever

You have severe community-acquired pneumonia and there is no clear cause

You are a healthcare worker who works directly with patients and you have a respiratory illness and a fever “There is a global shortage of the test kits that pathologists use to diagnose COVID-19,” the website said. “This is why we are doing targeted testing instead of widespread testing.” But Professor Komesaroff said: “The short answer is we should be testing more.” Who else should we be testing? Professor Komesaroff said that at the very least doctors should be able to refer patients whom they suspected might have COVID-19 for testing, even if they did not meet the criteria.

“The reason for the relatively rigid guidelines has obviously been a shortage of availability of testing kits, with demand placed on them very early by people who were well. That was a waste of resources but that doesn’t mean the criteria should be dogmatically applied and tests restricted to a very limited number of people.” Professor Komesaroff said the need for doctors to have the ability to order tests was amplified by the fact an increasing number of cases were locally transmitted. “If we just focus on people known to be at risk who have come from overseas, we are not testing people in the community.” Professor MacIntyre said if we could not procure or make enough tests, we could ask South Korea for help, as the US was doing. Loading Replay Replay video Play video Play video

Should we also be testing people without symptoms? Professor MacIntrye said we should also be testing people without symptoms who were in high-risk groups. These included close contacts of people with COVID-19, evacuees from cruise ships and people in closed outbreak settings, such as aged care centres, prisons, boarding schools, Indigenous communities or a military base. Professor MacIntrye said that when the Diamond Princess was quarantined in Yokohama for two weeks, Japanese authorities tested everyone on board.

“They found about one-third of passengers were infected and about half of those didn’t have symptoms,” she said. Meanwhile, earlier this month 2700 passengers were infamously allowed to disembark from the Ruby Princess cruise ship in Sydney, despite several people on board being tested for coronavirus. Hundreds of cases have now been linked to the ship. Professor MacIntyre said there were probably people who were on the ship but had been asymptomatic spreading the virus without realising. “Unless there is testing of high risk asymptomatic people you will never trace those people who will be continuing to transmit in the community,” she said. But Professor Stephen Turner, the head of the department of microbiology at Monash University, said that at present under 2 per cent of the coronavirus tests in Australia were coming back positive.

He questioned whether there was much value in testing people without symptoms until the level of transmission had grown. Sign up to our Coronavirus Update newsletter Get our Coronavirus Update newsletter for the day's crucial developments at a glance, the numbers you need to know and what our readers are saying. Sign up to The Sydney Morning Herald's newsletter here and The Age's here. What about the future? Professor Turner said it was going to become important to understand who had been exposed to the coronavirus and recovered. He said the swab tests, which were currently used, only identified those who were infectious.

However, blood tests that should be available soon - known as serological testing - identified those who had developed immunity. “That’s when we get to have an idea about the level of exposure. Depending on how widespread it is we might be able to look at winding back some of the restrictions in due course.”