People who become sick with COVID-19 are not retested before leaving isolation because the vast majority of transmission to others occurs at the beginning of the illness says the state's Public Health director.
Public Health director Mark Veitch said, as in all viral infections, people with COVID-19 were most infectious around the time they first become sick.
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"For a day or so before they become sick, when they become unwell on that first day and for a couple of days afterwards," Dr Veitch said.
"They feel rotten because they have got a virus circulating through their body and they are most infectious at that stage.
"That's when most of the transmission of a virus will occur. It can also continue for a few days onward as people have symptoms.
"People with most viral infections recover from those infections over the course of a few days or a week or two. As they recover the amount of virus in their body progressively declines."
Dr Veitch said it was the case with many infections a person who had recovered from their illness could, if tested, be found to carry evidence of the virus.
"Being able to find it doesn't mean they are infectious to other people," he said.
"We know, for example with HIV infection or hepatitis B infection, we can pick up those chronic infections in people for years but those viruses can be present in the blood and body fluids at a level where it can't be transmitted to people.
"It's not quite the same analogy with a respiratory infection such as coronavirus infection but my point here is, we know from our experience this year, if you test people who have recovered from the infection one, two, three or even four weeks out you can pick up evidence [of the virus] with the very sensitive tests we are able to use.
"Our current guidelines are based around the time from someone's illness onset, and we say from when 10 days have passed from your illness onset and a further three days from when your symptoms are finished you can be released to circulate in the general public and adopt, as everyone should, social distancing measures."
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Dr Veitch said testing of members of the general public recovering from COVID-19 was not done because there was no evidence the virus had been transmitted to other people this way.
"We have taken a more cautious approach in relation to health care workers. The national guidance is to require people who are health care workers or aged care workers to have two swabs done to make sure that there's no virus in their respiratory tract when they go back to work," Dr Veitch said.
"Even saying that, we don't have evidence of convalescent health care workers creating problems with infections in their health care settings."
Premier Peter Gutwein said health authorities' position on this was sound.
"There has been vigorous debate on this and I don't mind saying I've questioned Public Health extensively in regards to this," Mr Gutwein said.
"On face value, it seems like something that should occur or could occur, but the public health arguments are quite firm.
"Obviously, guidelines change over time but at the moment Public Health's view is that that should not occur."