Three of the 11 Rangitoto College group, who travelled to Mexico, have tested positive for swine flu - enough evidence to confirm all 11 cases as the virus.
In a press conference just after 9pm on Tuesday, Minister of Health Tony Ryall announced that four of the Rangitoto group's samples had been tested by the WHO lab in Melbourne and three of those have returned positive results for swine flu.
"Officials have advised me this evening that is sufficient to indicate that swine flu is the cause of the illness experienced by the Rangitoto group.
"Their symptoms were mild and they all are recovering, this is the pattern seen outside of Mexico," says Ryall.
He says it can now be confirmed that there are 11 cases of swine flu in New Zealand and 43 suspected cases.
"We took a cautious and appropriate approach by treating all of these affected travellers as probably positive while we were awaiting the test results," Ryall says.
Following the results Ryall says the time period covering the public advisory has been changed. Anyone who has been in the United States or Mexico in the last seven days and is displaying flu like symptoms should contact their GP.
Ryall says there's no need to be alarmed, but it's a time to be cautious.
Director-General of Health Stephen McKiernan says they're managing to contain the spread of swine flu.
He says they're fortunate that they were able to act early, and so the provision of Tamiflu to family contacts and to the rest of those on the plane was with containment in mind.
There are 43 other suspected cases around the country.
No deaths outside Mexico
The swine flu death toll in Mexico is at 149, but foreigners who've contracted it have become only mildly ill and there have been no deaths outside Mexico.
More than 50 infected people have been found in the United States, six in Canada and three across the Atlantic in Spain and Scotland. Possible cases are also being tested in Norway and South Korea.
The Rangitoto College group returned to New Zealand on Anzac Day at 5am on Air New Zealand flight NZ1.
Initially 10 of the Rangitoto College group tested positive for influenza A, the swine flu parent virus, but it emerged on Tuesday that another person from the group also has influenza A and will now be tested for swine flu.
Three students from Northcote College, who had also been to Mexico, returned negative results for influenza A.
Symptoms of swine flu in people are similar to those of seasonal influenza - sudden onset of fever, coughing, muscle aches and extreme tiredness. Swine flu appears to cause more diarrhoea and vomiting than normal flu.
While there is no treatment specifically targeted at the virus the Tamiflu anti-viral drug has proved successful in treating it so far.
From Friday, Tamiflu will be available over the counter in pharmacies.
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