Two people are dead and more than a dozen are sick after a suspected norovirus outbreak.
The outbreak has shut part of an Auckland rest home where more than 180 elderly people live.
The clinical director of the Auckland Regional Public Health Service, Dr Julia Peters, said last night that everything was being done to contain the spread of the highly contagious illness.
Outbreaks of norovirus were not unusual, but deaths were uncommon, Dr Peters said.
The Institute of Environmental Science and Research says 10 people died from the virus last year.
Those hit by the latest outbreak all live at St Andrew's Village, a 14ha retirement centre in Glendowie which offers services from specialist hospital care to rentalcottages.
The hospital section of the centre has been closed to visitors after an outbreak of gastroenteritis, which the Public Health Service said was probably caused by norovirus.
The two people who died were in hospital with other illnesses so it could not be said for sure that norovirus had killed them, Dr Peters said.
"But if elderly people are debilitated and already hospitalised, they are hit harder than a healthy person, who can shake it off."
Another 13 people were struck down with the symptoms of vomiting and/or diarrhoea, but Dr Peters said about half were showing signs of recovery.
St Andrew's Village management was not available for comment last night.
Although there have been larger outbreaks of norovirus, this is understood to be one of the most deadly.
Dr Peters said steps taken to manage the outbreak included isolating affected patients, making sure hand hygiene was thorough, and extra cleaning of surfaces likely to becontaminated.
"It is all being done by the book - they are doing everything they can."
Dr Peters said norovirus was not uncommon in institutions and was very contagious.
Samples had been sent for laboratory testing, and results were due back early next week.
Dr Peters said it was not always possible to determine the cause of an outbreak.
"It could arise from a range of possible internal or external contacts with patients. Unfortunately this is not unusual and there is a higher tendency towards outbreaks of this type in elderly institutions."
There were understood to be 180 elderly people living in the village, which included the hospital, a rest home and independent accommodation.
Last month, Dunedin Hospital returned to business as usual after waves of norovirus outbreaks, which resulted in a lockdown at the hospital towards the end of August.
More than 170 staff and patients were affected, but no one died.
At least 2300 procedures, outpatient visits and planned admissions were postponed as hospital staff fought to control the spread of the virus.
There have been other reported outbreaks of norovirus in rest homes this year, including at Greymouth and Whangarei.
Symptoms include abdominal pains, fever and headache, and usually begin between 10 and 50 hours after the virus enters the body.
They usually last for 12 to 72 hours.
* Highly contagious cause of gastroenteritis.
* Easily spread when people eat or drink contaminated food and fluids.
* Symptoms, including nausea, vomiting, abdominal pain and diarrhoea, usually occur 10 to 50 hours after consumption of the virus. Headache, fever and chills may also occur.
* Attacks usually last 12 to 72 hours, but some people may be unwell for longer.
* There is no specific treatment - the immune system eventually overcomes the virus.
* Last year, 206 outbreaks affected 5902 people, killing 10.