Queensland has 42 untraceable cases of coronavirus which authorities cannot find an epidemiological link to. So what are the complexities of tracing the virus and could Queensland ever rid itself of it?

Queenslanders are being warned not to assume we have beaten coronavirus and āit is unlikely that we will, everā despite a large drop in cases.
Chief Health Officer Dr Jeannette Young said 42 Queensland cases of COVID-19 have no traceable source, including an infected nurse working at a Rockhampton aged care facility.
āThese are the cases that worry me,ā Young said.
āThis is why we cannot assume we have beaten this virus ā we havenāt.
āIt is unlikely that we will, ever.
āWeāll have to find ways of managing it and the hope of course is for a vaccine to assist us in that.ā
Queensland has moved to stage one relaxation of restrictions with small groups of people allowed to dine at restaurants, cafes or pubs.
Young said the infected nurse was the only case in the past two weeks where an epidemiological link had not been established.
āWe know we are getting cases out there in the community,ā she said.
āWe had more cases earlier on, when we were having those 60 cases a day where [we] couldnāt find epi links.ā
Young warned people not to become complacent.
āIf you have respiratory symptoms thereās every chance it is more likely due to COVID-19 than it is due to anything else,ā she said.
āWe do know that people can have asymptomatic disease ā no symptoms at all ā and can spread the virus.
āTownsvilleās not had a case for quite a while [so] donāt think āI live in Townsville, therefore I donāt have to worry that that sore throat and that cough [means] that Iāve got COVIDā, it could very easily be COVID.
āIn actual fact, we have possibly got more respiratory disease in our state at the moment due to COVID-19 than we do due to flu.ā
Authorities have urged anyone in the state to get tested for even the mildest symptoms of cold or flu.
University of Melbourne epidemiologist and public health medicine specialist, Professor Tony Blakely said an epidemiological link was tracing how someone contracted the virus.
āAn epi link in the context of COVID is whereby if a case occurs you can track back from that case to where they got the infection from,ā Blakely said.
āIn contrast to that, a non-linked one, or one that just occurs, you canāt find out where they got the virus from.ā
The Australian Department of Health says an epidemiological link can be established when two factors are at play.
The first is contact between two people when one of them is likely to be infectious and the other has an illness that started within the incubation period after this contact.
The second factor is when at least one case in the chain of epidemiologically linked cases (which may involve many cases) is laboratory confirmed.
Blakely said going back through confirmed coronavirus cases to establish an epi link was a complex process.
āOn average it takes about five or seven days for somebody to incubate the virus, so the further back in time [you go], the more steps you have to go back,ā he said.
āBut thatās an average ā some people may take up to two weeks to incubate the virus, for example.
āIt depends on the number of people theyāve seen, because the fewer theyāve seen the easier it is to contact trace.
āIt really is a moving feast.ā
Blakely said Queensland was not in a bad position if it only had one untraceable case of COVID-19 in the past fortnight.
āItās a concern but itās nowhere near as bad as some other places with more of those cases occurring in the last two weeks,ā he said.
āIt is still possible if Queensland keeps its borders really locked, and goes really hard on contact tracing that maybe theyāll get rid of all the community transmission.
āWhat you can say with some confidence is in places where youāve still got community transmission and youāre opening up, youāre going out more, youāve got bigger group size meetings, [the] chance of that community transmission taking off is real.
āWhat happens in Queensland, only time will tell.ā
Queensland Premier Annastacia Palaszczuk said the stateās border with New South Wales could remain closed until at least September.
ā ABC / Kerrin Binnie and Rachel Riga
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