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How one man's beers with a few workmates dragged us all deeper into pandemic

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Health authorities say a man from Melbourne is “likely” to have sparked Sydney hotel cluster as Victoria records worst day so far with another 317 infections.

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The man, who works for a freight company but is not a truck driver, travelled to Sydney on June 30 and is thought to have infected several colleagues at his workplace.

The group went to a function at the Crossroads Hotel on July 3.

“We’ve made these links with extensive interviews over multiple public health units,” NSW Health’s Jennie Musto said.

“The man from Melbourne didn’t think he was particularly unwell and didn’t think he was sick with COVID.

“He’s been in New South Wales for a while, and it wasn’t until we interviewed him and his colleagues with more detail that we made the link that they were all at the Crossroads on the third of July.”

So far, 34 COVID-19 infections have been linked to the pub.

The man, and up to three others, were believed to be infectious when they attended the pub.

NSW chief health officer Kerry Chant said genomic testing had confirmed the COVID strain was the same one being spread in areas of Melbourne.

Victorian Premier Daniel Andrews said that of the record daily increase in cases, 28 were connected to known outbreaks and 289 were under investigation.

“One of the key challenges board the fact this is wildly infectious and you come infectious and only have very mild symptoms, the life cycle of this virus means that actions you take today, the impacts of which are not clear or well known or understood or reflected in data for at least a week, and to be safe, really, two weeks’ time,” Andrews said.

NSW Health Minister Brad Hazzard said people should not blame Victoria for the resurgence of the virus in Sydney.

“Our focus is to make sure that our community is kept safe,” he said.

The Crossroads outbreak prompted Queensland to tighten its border restrictions. Deputy Premier and Health Minister Steven Miles said 19 people found to have visited the hotel before entering Queensland had so far tested negative.

Amid continued traffic delays at the border, where around 1100 vehicles have been refused entry since Friday, Miles said it was important that Queenslanders remained vigilant.

“The most difficult thing to manage now is complacency,” Miles said, after another day with no new diagnoses and with Queensland still having just four active cases.

Health authorities in NSW on Wednesday confirmed four new coronavirus infections linked to a cluster of cases at the Crossroads Hotel.

The case highlights the speed and terrifying efficiency with which the virus can be transmitted by so-called “super-spreaders”.

A Melbourne man visits a busy pub in south-west Sydney with several workmates on July 3, and 12 days later 34 COVID-19 infections have been linked to the Crossroads Hotel.

A woman with no symptoms returns to China from the US and is self-quarantining at home, but after using the lift in her building alone sparks a cluster of 71 cases.

A choir practice in the US leads to 52 people being infected with the virus and two of the singers dying.

These are all examples of coronavirus superspreader events, where one or a few infected people spread the virus to many others.

But how do such events occur? Let’s unpack what being a superspreader means.

While it’s easy to imagine people infected with COVID-19 have equal chance of transmitting the virus to others, it turns out that’s not what happens most of the time.

In fact, the pandemic sweeping the globe seems to follow a pattern seen in many other infectious diseases, where it’s been observed that only a small proportion of those infected control the bulk of transmission events.

This has sometimes been dubbed the 80/20 rule because about 20 per cent of people control about 80 per cent of the infection spread.

The rest of the time —  the majority of the time — the virus doesn’t spread from an infected person to anyone else at all, but rather the transmission just peters out.

Such individuals who infect a disproportionate number of others have been called superspreaders.

People can be superspreaders for a variety of reasons.

These might be biological (they might have particular genes that make them more infectious), behavioural (they might socialise widely, creating more opportunities for infection spread) or simply a random event (they might have been in a crowded room at just the time when they were most infectious).

Some experts argue superspreading events are of greater interest than superspreaders themselves.

This is because often there is nothing unusual or unique about the person involved, but rather they were in the right place in the right time to trigger a large chain of infections.

Labelling someone a superspreader may unfairly stigmatise them.

There is also the chance some transmissions that were in fact due to other people were missed, making someone look like more of a superspreader than they really were.

Any individual could be a superspreader given the right circumstances, which is why measures like physical distancing, hand hygiene and getting tested and self-isolating if you have symptoms are crucial for everyone.

Identifying superspreaders can be useful though because efforts targeted at them could offer more ‘bang for buck’ in containing outbreaks.

For instance, contact tracing — which aims to identify other people who an infected person might have passed the virus onto — is often very labour intensive.

But the effort is more worthwhile for a superspreader than for someone who doesn’t pass the virus onto anyone else.

As well as the Crossroads Hotel event mentioned above, Professor Marylouise McLaws from UNSW Sydney said the recent explosion in transmission in Victoria stemmed from a number of clusters which could be considered superspreading events.

The clusters involved security guards at quarantine hotels connected to large family gatherings.

Another cluster emerged in a public housing tower where a combination of the physical environment (communal spaces, cramped living conditions and even ventilation) and employment patterns (many of the residents worked in essential jobs that exposed them to many potentially infectious people) may have created a ‘perfect storm’ for superspreading.

At the Newmarch House nursing home in western Sydney, one infected staff member led to the deaths of 19 residents, and 37 residents and 34 staff testing positive for the virus.

Speaking on the Coronacast podcast today, the ABC’s Dr Norman Swan said people need to be careful in pubs, restaurants, gyms and even their own homes.

“Pubs are potentially superspreading environments,” Swan said.

“In a pub you speak more loudly because you’ve got to be heard … and you are drinking therefore you’re disinhibited and you’re more likely to be laughing, chatting to your mates.

“It’s just the environment where if you’ve got the virus, it’s coming out and it’s going significant distances.”

-ABC/ Cathy Johnson and science reporter Suzannah Lyons

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