The first sign the hospital was dealing with the contagion came on Thursday and a full Infection Control outbreak response was activated, he said.
It is not easy to contain a virus as infectious as norovirus. "But it has been our experience at Northland DHB, if we act early and decisively, then we can usually contain an outbreak within a few days."
The fast-spreading noroviruses are a group of gastrointestinal viruses that lead to vomiting and diarrhoea.
For most people it is not a serious illness and they recover after a couple of days, but the elderly, very young and sick are particularly vulnerable.
"It tends to come and go but we are currently seeing a lot of cases in the community. Although it is referred to as the 'winter vomiting bug' in the Northern Hemisphere, it usually seems to strike New Zealand in the summer season. This year 'summer' appears to have arrived early," Dr Hammer said.
"Norovirus symptoms include vomiting, diarrhoea, stomach pains and feeling like throwing up."
A man who asked not to be named as his wife is in Ward 1 said soon after he had visited her on Thursday evening, she called to say staff were advising patients to tell visitors to stay away. She is one of the patients in isolation.
"My wife is in the more vulnerable group. She's got two bone infections and now she's got this. That's three infections, and she's very weak," he said. "It's no-one's fault and staff are doing everything they possibly can."
People with norovirus are usually sick for two days but can be infectious for three days after the symptoms stop. They should drink plenty of fluids to avoid becoming dehydrated.
Good hand hygiene is critical. Norovirus spreads via contaminated food or drinks, touching contaminated surfaces, direct contact with an infected person and through contaminated particles in the air.
