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‘Fifty-fifty chance’ NSW will see surge in cases as clusters grow

“All of us have the concern that when you have even a couple of unknown sources of a virus, that can have tragic consequences if you don’t focus your energies on tracing down each and every case and making sure you’ve ring-fenced every known cluster,” she said.

Epidemiologist and lecturer in international health at the University of NSW Abrar Ahmad Chughtai said NSW ran a “fifty-fifty chance we’ll see a surge in cases” like that of Victoria.

“We still need to be really careful,” Dr Chughtai said.

The time it takes to identify cases, the speed of contact tracing and the number of asymptomatic cases determine the likelihood of each cluster becoming a “super spreader” event.


“It’s a chain of transmission, if I pick up the virus at a hotel and then infect four people, they’ll go in four different directions, one could go to the gym, one could go shopping, and they’ll spread the infection further,” he said.

“You can’t predict that, if you have some cases who spread the infection more, the cluster will be very large. In other cases, if someone is infected and isolates straight away, it’ll be much smaller.”

The number of cases linked to the Potts Point cluster and a separate cluster of funerals in Sydney’s west are still rising, nearly three weeks after the first associated events in mid-July.

On the other hand, the number of new cases linked to the Crossroads Hotel cluster slowed to nearly zero about three weeks after July 3 – the date which the infection is believed to have spread initially.

Dr Chughtai said NSW is facing a different challenge to Victoria, with a small but steady number of new cases being reported every day.

“How large epidemics start is you see a seeding of cases,” he said.

“When there’s enough seeding in the community, you start to see large outbreaks. Due to breaches in quarantine in Victoria, they weren’t aware of the seeding until it was too difficult to control.”

People in NSW learnt from this Victorian experience and came forward to get tested early “so we don’t have the seeding to the same extent, but [the risk] is still there”, Dr Chughtai said.

Health authorities identified mystery cases with no known source and no links to clusters as one of the biggest concerns.

There continue to be a handful of these cases of unknown origin every week in Sydney.


On Wednesday, NSW Chief Health Officer Dr Kerry Chant implored people to come forward for testing in south-west and western Sydney, specifically in Cumberland, Parramatta, Fairfield, Bankstown, Liverpool and Campbelltown.

“I would urge those communities in those local government areas to particularly with the most minimal of symptoms please come forward and get tested,” Dr Chant said.

“It is essential that we find any as yet undetected chains of transmission and break them. The earlier we find these chains of transmission the earlier we can stop it.”

She asked the public to “redouble your efforts” on testing to ensure health authorities could contain the spread of the virus.

Health authorities are often eventually able to detect the chains of transmission for mystery cases with no known source after contact tracers reinterview those infected and find they had forgotten that they had visited a venue implicated in a known cluster.

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