FIVE people have died and four nursing homes quarantined after an outbreak of flu in the NSW Hunter Valley.

Cases of influenza A, which this month claimed 10 lives at Newcastle´s Bethel Aged Care Facility, had been confirmed at three nursing homes, Hunter Health´s Dr Tony Merritt said.

But it has not been confirmed whether the deadly flu was responsible for five deaths since Saturday at the fourth home.

Dr Merritt said the five residents, aged 70 to 93, were among a number of residents at the unnamed home who showed symptoms of a flu-like respiratory illness over the past week.

"While each of the five residents had some signs of respiratory illness before they died, at this stage influenza has not been conclusively linked to their deaths," Dr Merritt said.

"Initial testing at the facility has been negative for influenza, but further testing is under way."

Dr Merritt said about 80 residents across the four privately owned facilities were suffering from respiratory illness.

Influenza A had been confirmed in seven residents at three homes, he said.

All the homes, which Dr Merritt would not name, have been quarantined since Friday, closing their doors to new residents and non-essential visitors.

Hunter Health has recommended that residents at the three facilities where influenza has been confirmed, and who have not yet been infected, take a preventative course of anti-viral medicine.

Dr Merritt said that after the flu outbreak at Bethel, Hunter Health contacted all aged-care facilities in the Hunter, urging them to implement measures to contain the spread of the illness.

Frail, older people ?particularly those in residential care facilities ?as well as those with underlying health issues, were most at risk of developing a serious infection, Dr Merritt said.

There was also an increased level of flu in the Hunter community, he said.