These charts show the vast scale of Sydney's current flu outbreak, the biggest in years

Australia’s biggest city is in the grip of a huge flu outbreak.

Hospitalisations for flu have spiked across Sydney and more than 8000 cases were laboratory confirmed in a single week at the start of August.

More than 50 outbreaks in institutions were recorded, almost all of them in aged care facilities.

This chart, taken from the NSW state government flu surveillance report for the week ending August 6, shows the number of lab-tested cases confirmed as flu. What’s unusual is that there are high numbers of both influenza type A and B.

Here’s another way of looking at that data, showing the rates of diagnosis with more historical context. Again you can see both type A and B surging at the same time. The A rate is not especially unusual, but the combination of both main strains is:

NSW Health

The number of patient samples testing positive for flu exploded from just 5.5% at the beginning of July to more than 30% at the start of August.

This next chart shows the number of emergency department presentations for flu-like symptoms. The black line is this year, showing the dramatic comparison between this year and what doctors would normally be expected to be dealing with.

NSW Health

It’s not just people showing up at emergency departments — a huge number of people are being fully admitted to hospital for treatment. Here’s the admissions chart, showing hundreds of people are so sick they need to stay in hospital for treatment.

NSW Health

The data shows that the outbreak has spread around the city, with almost all local health districts reporting increases. It appears to be particularly intense in the city’s north and west, however, however, with the rate per 100,000 people exploding from an average of 53 over the previous four weeks to 126. The rate in the Blue Mountains area rose from 57 per 100,000 to 129, while in western Sydney the rate spiked from 67 to 106.

Northern Sydney saw its number of official flu notifications spike from an average of 482 over the previous month to 1154.

These numbers are only the cases the have been laboratory confirmed. People suffering with the flu who tackle it with over-the-counter medicines and don’t visit a doctor, or are never tested, are not included, so the number of infections is likely to be far higher.

Experts have been warning that Australia could be witnessing its biggest ever flu outbreak. “It’s in everyone’s interest to get a flu shot, there’s still time.”

Professor Paul Van Buynder from Gold Coast Health and the Immunisation Coalition said last month: “It looks like we will again get the greatest number of notified cases in Australia we’ve ever seen.

He said he was “confident that this is not just the biggest recorded year in our data but it’s also the largest flu outbreak that we’ve seen for quite some time.”

Vaccinations are still effective for people who have not caught the virus yet.

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