Health authorities are warning influenza is not the only illness to be concerned about this winter.

Key points: Cases of croup have increased by about 15 per cent this year in Queensland public hospitals and Sydney's Children's Hospital at Westmead

Cases of croup have increased by about 15 per cent this year in Queensland public hospitals and Sydney's Children's Hospital at Westmead Cases of pneumonia have also increased this year

Cases of pneumonia have also increased this year Doctors believe both increases are linked to this year's bad flu season

There has been a spike in hospital presentations of both pneumonia and the childhood condition croup in recent months.

"It's a busy year for respiratory presentations," Geoff Pearce, a senior medical officer in the emergency department at the Queensland Children's Hospital, said.

"Every night we would see half a dozen cases of croup."

Croup is an inflammation of the air passages, is usually caused by a specific virus called para-influenza, and is more common in cooler weather.

Data analysed by 7.30 shows croup presentations have increased by about 15 per cent at Queensland public hospitals and the Children's Hospital at Westmead in Sydney this year, compared to similar periods during the past three years.

Professor Robert Booy, from the National Centre for Immunisation Research and Surveillance, said this spike might be because of the influenza virus, which was more widespread than usual this winter.

"So maybe both viruses [para-influenza and influenza] are leading to croup," he said.

"And to a smaller extent, the surge of 15 per cent to 20 per cent can be put down to a second virus causing trouble."

'It was quite terrifying'

Brisbane parents Kylie and John Kirkegaard are feeling nervous about this winter.

Their toddler, James, first caught croup in the summer and has had five attacks since then, but medication does keep it under control.

"We're keeping a very close eye on him … we just need to be prepared," Ms Kirkegaard said.

James's father vividly recalls the first time his son had croup.

"It just sounded like this really seal-type barking cough, it was quite terrifying," Mr Kirkegaard said.

Dr Geoff Pearce says he is seeing half a dozen cases of croup of every night in the emergency department at Queensland Children's Hospital. ( ABC News: Chis Gillette )

Dr Pearce said croup could be "extremely worrying for parents".

"It's something they usually haven't heard before in their child," he said.

"Anyone having difficulty breathing is very scared and it's natural for their kids to be very scared.

"The best thing you can do as a parent and care-giver … is to stay as calm as possible."

People 'need to know' about pneumonia vaccination

Meredith Lores had pneumonia in March. ( ABC News: Chis Gillette )

The increase in pneumonia presentations this year is almost certainly linked to the bad flu season, according to Professor Booy.

"Influenza and pneumonia go hand in hand," he said.

People aged over 65 or with a pre-existing lung problem are most at risk.

"Colleagues of mine here in Australia have shown that if you're admitted to hospital for pneumonia over the age of 65, you've got a 10 per cent risk of coming out in a coffin," Professor Booy said.

The good news is that there is a vaccine for pneumonia.

Meredith Lores caught pneumonia in March, and has since been vaccinated because she has a history of lung complaints.

"The flu vaccine, everyone knows about. The pneumonia one, people don't know about it, so that's something they have to know and get sorted," she said.

Professor Booy said the lack of awareness about the pneumonia vaccination was "a real concern".

"So many people could be protected, but they're not. They need to know," he said.

"[There is] a very safe and effective vaccine that prevents the complications of pneumonia, that reduces the risk of hospitalisation, and reduces the risk of dying from pneumonia."