Ten Rangitoto College pupils have tonight tested positive for influenza with health officials saying they consider it "likely" they have swine flu.
Swine flu is believed to have killed more than 80 people in Mexico and over 1300 are sick as a result of catching the virus which has also hit parts of the United States.
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Health officials said tonight there were also three other high schools at risk with pupils from Northcote College having recently returned from Mexico, while Pinehurst and Westlake Girls High also had pupils in the United States and South America.
Health Minister Tony Ryall said most of the flu-affected pupils from Rangitoto College were on the "road to recovery", but other pupils had since come down with flu-like symptoms. Twenty-two pupils and three teachers were on the trip with 14 showing flu-like symptoms.
The affected pupils were being kept in isolation at home along with their family members.
One pupil was taken to hospital on Saturday, but was not in a serious condition.
Dr Darren Hunt, deputy director of public health, said it could take days till they knew whether the influenza was H1N1 swine flu - a subset of Influenza A.
Melbourne health authorities were being contacted and would carry out the tests.
Until results were known, health officials are treating the situation as if the victims had swine flu and have upgraded the country’s health alert status to "code yellow".
"I think it is important to recognise the concern that we have and [that] the deaths that have been reported from Mexico.
"At the same time the cases that have been reported from the United States seem to be relatively mild and there haven't been any deaths reported from the US," Dr Hunt said.
While it was a new flu strain, patients that had been treated with Tamiflu had responded, he said.
At this stage health officials had no plans to order more Tamiflu as pharmacies still had "quite a bit in stock," Health Ministry pandemic planning co-ordinator Steve Brazier said.
Officials stressed however, that anyone with flu symptoms should visit their doctor and not treat themselves.
Doctors and nurses would also be stationed at Auckland International Airport from early tomorrow to screen for possible symptoms from travellers landing from North and Central America.
Officials would also seek fellow passengers onboard Air New Zealand's NZ1 Los Angeles flight that landed early yesterday and carried the affected Rangitoto College pupils for testing.
They could not say whether it was likely that other passengers onboard the Air NZ flight could have contracted the virus, but it was of concern.
"These people on the plane… may have been infected," Dr Hunt said.
Anyone who had gone to Mexico or North America should urgently contact their doctors if they felt unwell, he said.
Air New Zealand said tonight that 364 passengers were onboard the NZ1 flight.
The airline said it was is in close contact with the Auckland district health board and the Health Ministry and reiterated advice that passengers onboard should consult with their GP or other health professionals if they developed flu-like symptoms.
"Air New Zealand is supplying that same information to its crew through its medical team," it said in a statement.
Middlemore Hospital had released Tamiflu to the Auckland Regional Public Health Service to treat the patients and people who had been in contact with them.
The Ministry was in contact with the World Health Organisation and was liaising with Australia in terms of their response.
The Ministry was also working closely with Auckland Regional Public Health, district health boards and other Government agencies including MAF, Customs and the Ministry of Education.
It would keep New Zealanders informed of developments, Mr Ryall said.
- with NZPA