Do I have COVID, flu or something else?

After two years with virtually no cases of influenza in Australia, cases and hospitalisations are now ticking up – and we’ve now got COVID-19 to deal with as well. So what do we need to know about this year’s flu season, and what questions still remain to be answered?

Catch up on Part 1 in this series: How bad is the ’22 flu?

How do you know whether you have COVID or flu?

It’s clear that there are plenty of winter lurgies of one kind or another going around at the moment – so if you’re feeling unwell, how can you tell which disagreeable respiratory disease has struck you down?

While COVID-19 and flu can both cause more severe disease than something like a common cold, there’s no good way to tell what you have based on symptoms alone. A runny nose, sore throat, cough or sneeze are common to all three diseases. Both COVID-19 and influenza are also known to cause fevers, head and body aches or pains, and diarrhoea or vomiting.

The only way to know for sure if you have COVID or flu, experts say, is through PCR testing. Such tests, which target a specific part of each virus’ genome, are able to confirm or rule out both SARS-CoV-2 and influenza infections. Like COVID tests, flu tests are generally performed on a nasal or sometimes throat swab.

How does flu testing work?

While seeking a PCR test for COVID-19 may now feel almost routine, a PCR test for influenza generally needs to be ordered by a doctor.

Adrian Esterman, an epidemiologist and professor of biostatistics at the University of South Australia, suggests asking a GP about the likelihood of influenza if you have cold or flu symptoms and a negative PCR result for COVID-19.

“There are a number of sentinel GP practices around Australia, and if you go to see your GP and you’ve got upper respiratory symptoms, then the GP would actually send the sample off for flu [testing],” he explains.

Confirmed flu samples may be further analysed to track which influenza strains are circulating – which feeds into the vaccine development for the following year.

Covid or flu concept a young woman having her nose swabbed for a pcr test
A PCR test is a reliable way to diagnose whether you have COVID-19 or influenza. Credit: Luis Alvarez / DigitalVision / Getty Images.

As we move forward, it’s possible that COVID-19’s very emergence will make influenza more difficult to track.

“A lot of our estimations of flu come from what we call ‘influenza-like illness’,” explains Daniel Layton, an immunologist at CSIRO. This categorisation is based mainly on patient symptoms, which can be very similar for COVID-19 and flu.

“It’s quite possible that the presence of COVID now will make it harder to track influenza – being diagnosed with something like a PCR test may actually become more important,” he says.

Can I get a RAT for influenza?

Rapid antigen tests for influenza do exist, but they’re not widely available.

“Prior to COVID, there wasn’t necessarily a public appetite for them,” says Kirsty Short, an NHMRC research fellow specialising in influenza and COVID-19 at the University of Queensland. “I do suspect that as we move on, probably what you’ll have is at-home respiratory virus RATs, where you can quickly diagnose which respiratory virus you have.”

Such RATs might be able to test for SARS-CoV-2, influenza and respiratory syncytial virus (RSV) all at the same time, Short says.

Read the next article in this series about the flu and COVID-19: How is having COVID around changing the flu season? or catch up on Part 1: How bad is the ’22 flu?

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