Nathan Brown was on life support at the John Hunter Hospital, where his family and friends had been keeping a bedside vigil for the past month as he battled acute pneumonia, a staph infection, collapsed lungs, kidney failure, and fluid on his heart.

His uncle, Peter Brown, told the Herald that Nathan had lost his battle on Friday morning.

Mr Brown said the distraught family had been praying their “very sick young man” would pull through it all for a positive outcome.

“It just goes to show that this flu can attack anybody,” Mr Brown said earlier in the week.

“It really can hit you no matter what age you are. If a very fit and healthy 19 year old can be struck down as badly as him … It has come as a big shock to everybody.”

A 38-year-old man is also in a critical condition at John Hunter Hospital, suffering complications from influenza.

Cases of influenza have quadrupled in the region since the same time last year, with Hunter New England Health confirming cases to date had risen from 2491 in 2016, to 9822 in 2017.

“It has certainly been a big influenza season,” Hunter New England Health physician Dr David Durrheim said.

“The tests that are available now do make confirmation of influenza much easier. But that does not fully explain all of the increase.

“These are only the confirmed cases, too. The majority of cases go through GPs, and the GP knows that a having a confirmed diagnosis is not going to change their advice. So these are just the ones where a swab has been taken to confirm flu.”

Dr Durrheim said people had “gotten used to the fact” flu could be catastrophic for the very old, and the very young.

“But we have seen it in Victoria this season as well, that people, previously considered very healthy, unfortunately get a really severe dose of influenza, and they get secondary complications and they just don’t do well at all.

“Influenza is no joke.”

He said approximately 20,000 hospitalisations across Australia were caused by flu and its complications.

“The national influenza specialist group estimates that every average year in Australia there are probably about 3500 deaths caused by flu,” Dr Durrheim said.

Mr Brown said his nephew – a keen fisherman and talented artist – had been working casually as a builder’s labourer before becoming ill about four weeks ago.

“On the Monday he was feeling unwell, and he ended up at Belmont Hospital, and then they transferred him to John Hunter Hospital,” Mr Brown said.

“Then on Wednesday he went downhill very quickly. By that time he was put into an induced coma.

“It has been a very stressful time for his family and his friends.”

The family initiated a GoFundMe campaign, which had been widely shared on social media and had raised close to $11,000.

It was set up in the hope it would support Nathan in his rehabilitation and recovery.

Mr Brown said the people who had donated had been “fantastic,” and their comments of support had been “very humbling” for the family.

Mr Brown urged people to be “vigilant” and seek a second opinion if their flu symptoms did not improve, or if they felt something was “not quite right.”

He said the doctors and nurses at the John Hunter had been “absolutely amazing,” doing everything they could to help the former Belmont High student.

To contribute to the fundraising campaign, visit gofundme.com/2mnzmg-support-for-nathan.

Dr Durrheim said there had been some concern that one of the strains covered in this year’s flu vaccine was not as good of a match to the viruses affecting people this season.

He said a lab in Melbourne was currently analysing the flu strains that had been circulating in Australia to find out “definitively” whether that was the case.

“They will know something within the next week or two,” he said.

“The northern hemisphere will be looking very closely at those results, because they have incorporated very similar strains in the vaccine they are using now in preparation for their winter season as well.

“Even though the vaccine is not a perfect vaccine, it is always worth protecting yourself, particularly those that we know are more vulnerable.”