How to read Victoria’s latest coronavirus data

On July 31 there were 5743 active cases statewide. That translates to about one in every 1000 Victorians, but the true rate is likely higher because of all the people out there with coronavirus who are asymptomatic, who haven’t been tested, or who are soon to receive the unfortunate news they have tested positive.

If your postcode is showing up as light grey on the map, it means there are no known active cases in your area. If it is a light shade of red then it means you live in an area that has a lower rate than most parts of the state.

If you’re having trouble finding your area, you can use the zoom settings on the side of the map. You can also drag the map view so that it shifts to the area you want to know more about. Alternatively, I have published a searchable table of all this information in this article.

Deakin University epidemiology chair Catherine Bennett warns people against being too optimistic if their postcode has a low number of active cases.

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“Three cases (in a postcode) doesn’t signal there are only three cases in a postcode. There could well be more you don’t know about,” Professor Bennett said.

“To suppress local transmission, masks just make that bit of difference. But it has to be Melbourne-wide or we will get another flare-up.”

The data shows that the highest infection rates are in the state’s north-west corridor, something which has been apparent long before the data was broken down by postcode.

The darkest spot on the map is the tiny 3022 postcode that takes in the suburbs of Ardeer and Deer Park, in Melbourne’s west, where there are 20 cases per 1000 people – that’s about 20 times higher than the rest of the state.

This area had 64 active cases as of July 31, which translates to about one in every 50 residents. But this postcode is where Estia Aged Care facility is located, the centre of an outbreak linked with 104 cases.

The data is broken down according to a person’s registered place of residence, not where they were infected or where they are currently living. It’s possible that some of the Estia staff live in 3022, but others likely live in nearby postcodes.

Many of the postcodes that have high rates of infection house large outbreaks, or adjoin areas that do.

Little River, between Melbourne and Geelong, currently has a rate of almost seven active cases per 1000 residents.

But keep in mind this area has nine active cases and a relatively small population of 1319, which means one or two additional cases there can have a sizeable impact on its infection rate.

I deliberately excluded areas with fewer than 1000 residents from the map for this very reason.

Also, the most recent population estimates we have for postcodes are from 2016, so if any area has grown substantially since then it means its infection rate on the map may be overstating the true extent of the virus’ spread to some degree.

Here’s a slightly different way of looking at the data on infection rates across Victorian postcodes. I’ve arranged the state’s postcodes with more than 1000 residents in a line from lowest known active case rate to highest:

All the greyed out areas are places where there aren’t any active cases right now, mostly ones in rural or regional Victoria. The red areas are places where there is at least one known active case.

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Those 10 narrow black bands at the end correspond to the 10 postcodes that were locked down in late June because of what Premier Daniel Andrews, at the time, called an “unacceptably high” rate of community transmission (that is, infections that cannot be traced to an existing case or outbreak).

These 10 postcodes are almost two weeks further into lockdown than the rest of Greater Melbourne and Mitchell shire, but as you can see from the graphic most still have amongst the highest rates of active cases.

Collectively there were 140 active cases in these areas on July 3; four weeks later that number had increased to 875.

But these are just two data points – we don’t know if those numbers have been going up and up in that time, or if they peaked some time ago and are now on the way down.

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Professor Bennett said community transmission had driven outbreaks in aged care facilities and workplaces in many areas with high infection rates, which was now, in turn, generating further community transmission.

“There are all these internal dynamics in epidemics you need to take into account,” she said.

“It’s the nature of the beast. The more community transmission, the more likely there is someone positive to take it into an aged care home. Then you’ve suddenly got a large number of cases, some of which is fed back into the community as well.

“It’s a cycle.”

During Saturday’s daily coronavirus update, Premier Daniel Andrews said public health officials were working their way through the data on community transmission numbers to decide on the state’s next step.

“You can’t be certain there isn’t even further community transmission, even more mystery cases out there,” he said.

“That is in some respects our biggest challenge.

“Nobody wants to see large numbers reported in any context, but if you can track back where the origin was then they are in a wholly different category to community transmission or mystery cases,” he said.

Since the start of the pandemic, there have been 1841 coronavirus cases in Victoria where community transmission is the suspected infection source, but the true number is higher because of the amount of time it takes to carry out these investigations.

“[Coronavirus] is a stubborn thing. There is no doubt about that it is a wicked enemy. You need compliance, that people are doing the right thing,” the Premier said.


Victoria’s coronavirus state of play: July


If you have any questions about the data, please leave a comment on this article or send me an email ([email protected]), and I will do my best to respond.

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