The Rangitoto College group at the centre of a swine flu alert originally thought they might be having a bad reaction to Mexican food.
Nine students and one teacher in the 25-strong party which arrived back in Auckland on Saturday morning after three weeks in Mexico have tested positive for influenza A.
Health officials believe it is likely they have swine flu, a deadly new strain of influenza A, which Mexican Health Minister Jose Angel Cordova says has now claimed 103 lives in Mexico.
Samples from the students who tested positive for influenza A are being sent to the World Health Organisation laboratory in Melbourne to ascertain whether it is the subset H1N1 swine influenza. The results should be back in a number of days.
Further measures, including greater surveillance, would be implemented if the influenza was confirmed as swine flu.
The Rangitoto school teacher stayed in North Shore Hospital overnight due to the symptoms of the disease, but she was expected to be discharged later today. A student was admitted on Saturday but has since been discharged.
All the infected students and their families have been quarantined at their homes.
The other students and teachers on the trip stayed home today as a precaution, while five students who played soccer with one of the returning students - who had no symptoms - were also sent home today as a precaution.
Click here for the Ministry of Health's influenza pandemic action plan.
In brief:
* Swine flu is a subset of the influenza A virus known as H1N1
* The virus has killed 103 people in Mexico and infected over 1600
* Twenty cases have been confirmed in the US, six in Canada
* There are suspected cases in France, New Zealand, Spain, Israel and Brazil
* Northcote and Rangitoto College groups returned from Mexico on Saturday
* Ten Rangitoto students have tested positive for influenza A and the group is being kept in home isolation
* Three Northcote College students and two Waikato residents are also being tested for influenza A
* Passengers arriving in NZ on North American flights are being screened and given information on the flu virus
* The potential influenza epidemic status has been upgraded to yellow
Three students from Northcote College who went on a separate trip and arrived back on a separate flight were also awaiting test results today.
Rangitoto College principal David Hodge said most of those believed to have the disease were responding well to doses of the anti-influenza drug, Tamiflu.
Mr Hodge has been constantly in touch with parents, health authorities and media since discovering the students may have contracted the disease on a three-week trip to Mexico.
"I became aware on Saturday that the kids had arrived home safely but aware that there had been illness on the trip," he told NZPA.
"Originally it was put down to Mexican food, which seemed like a good guess at the time."
The group were Spanish language students having three weeks in Mexico to give them language and cultural experience.
The group arrived in Mexico City and did a loop around the central part of the country before spending their last three days back in Mexico City, where the outbreak had centred.
"We are not overly concerned about the state of health of any of the students," he said.
"We were a bit concerned about the teacher because she remained in hospital overnight, but she is being well looked after. "
With all those who went on the trip being kept at home on public health advice, along with those closely connected to them and those involved in the Saturday soccer match, it had been business as usual at the school today.
"We have had a fair share of concern from parents wanting information, which is absolutely understandable," he said.
"What we don't want is for fear to take over."
Northcote College Principal Vicki Barrie said all of a 15-strong party which went to Mexico were contacted yesterday, and of them two students and a parent reported a mild sore throat. They had since been tested and were awaiting results.
Northcote College students were not due to return to school until tomorrow due to a previously scheduled teacher-only day.
Unlike the Rangitoto College group, most of the Northcote group spent little time in Mexico City.
"They arrived in Mexico City and then travelled through Mexico and they left from Cancun," Ms Barrie said.
"They came home on a different flight than the Rangitoto College party and arrived home at a different time on Saturday morning."
Meanwhile, Waikato District Health Board is investigating two possible cases of swine flu.
Waikato DHB spokesperson Amy Thomsen said the Waikato residents and those they had been in close contact with were being tested for influenza A after developing symptoms of the virus upon their return from the United States.
Both patients had returned to New Zealand within the past two weeks.
"Currently, as per Ministry of Health guidelines, Tamiflu will be prescribed for probable and confirmed cases and their household contacts (as appropriate)," said Waikato DHB medical officer of health Dr Anita Bell.
"So if these two test results come back as being positive, they will then be administered with the medication."
Dr Bell said the Waikato DHB was keeping in regular contact with the Ministry of Health.
Notification
A GP and North Shore Hospital physician notified the public health service of the possibility of influenza A infections on Saturday after treating the Rangitoto students.
"The advice from officials is that we should consider it probable it is swine flu," Health Minister Mr Ryall said.
Mr Ryall said the primary contact with passengers on both flights NZ5 had been through saturation media coverage.
Director of Public Health Mark Jacobs this morning told a media conference that the same process for travellers on board flight NZ5 would be followed as for NZ1 if the three Northcote students tested positive for influenza A.
Symptoms of swine flu take two to four days to present after infection and passengers on flight NZ1 or NZ5 who feel unwell should talk to their GPs.
Passengers who felt unwell would be offered Tamiflu, Dr Jacobs said.
But he stressed that New Zealand was entering influenza season and that travellers could experience flu-like symptoms that were not necessarily influenza A or swine flu.
"Many of you would know from experience how common it is to get symptoms of a cold after having spent a long time on a plane," he told media.
"People need to be reassured that what we're really talking about today is about a particular group of people that have been recently in Mexico or the US. The great majority of people in NZ that might be developing symptoms like this, they've just got a flu or a cold."
Dr Jacobs reiterated cases of influenza A on flight NZ5 had not been confirmed.
"At this stage there's nothing about NZ5 that makes it any different to any other group of people coming back from the US and Mexico, because we don't have confirmed cases of influenza A on that flight."
Dr Jacobs said he was happy with the way the suspected swine flu cases had been handled.
"Until late yesterday afternoon we didn't even know for sure these people had influenza.
"What they had was mild upper respiratory infection, so it could just have easily been a cold," he said.
"It could turn out to be one of the many other forms of influenza A."
Dr Jacobs said health officials had been reacting to information as it became available.
He said that only a small group of people would have had contact with the students and of the students themselves, very few were feeling unwell.
He said New Zealand was in quite a different situation to Mexico where there were potentially many infections but only a small number of tests for the virus had been carried out.
"The great, great majority of potential cases in Mexico still haven't been confirmed as linked to this particular swine flu," he said.
"It's still early days in terms of what we know but there's no indication it's any more infectious than any other strain of influenza."
Flight NZ1
Dr Jacobs told this morning's media conference it was "unlikely" the virus could have spread throughout Air NZ flight NZ1, which had 364 passengers on board.
He said those most at risk were people sitting beside an infected passenger, though influenza A could also be spread if someone coughed or sneezed on a surface later touched by someone who put their hands in contact with their mouth.
"In theory it's possible for it to spread through going to the airplane toilets and things like that. But the less direct contact someone's had with somebody with influenza on a plane, the lower risk they have."
Visitors to New Zealand could be harder to track down as they would not have given permanent contact details in New Zealand.
Clinical director of the Auckland Regional Public Health Service, Julia Peters, said while the weekend focus was on managing the sick school students, her staff would today be following up with other passengers.
"Now that we know that this is an influenza A virus, possibly the swine flu virus, our attention will definitely be turning to all the contact tracing.'
Dr Peters said the sick had respiratory illness symptoms including blocked nose, cough, fever, aching muscles, headache, loss of appetite, sneezing and watery eyes.
The sick and the well had agreed to stay in "home isolation" until the preliminary test results were known.
"Where there are non-symptomatic people, we have said other household members can go about their normal business," she said. "If the preliminary results are all clear it is likely we would be allowing people who are well to go to school and work [today]."
Passengers arriving in NZ
All passengers arriving in New Zealand from North America are being screened and given information about the flu.
They are also completing passenger locator cards so they can easily be contacted if required.
Mr Ryall has upgraded the alert level to code yellow - one below the highest code red. "[That means] increased surveillance and people arriving on North American flights will be told that if they have flu-like symptoms they should be in touch with their doctor or other health authorities."
Sick people should use tissues to cover sneezes and coughs; avoid contact with others and stay at home; wash and dry hands often; and avoid touching their eyes, nose and mouth.
Global spread
Canada today became the third country to confirm human cases of swine flu with public health officials reporting six people falling ill in Nova Scotia and British Columbia.
In the US, health officials said 20 swine flu cases had been reported so far in New York, Ohio, Kansas, Texas and California. There are also suspected cases in France, Israel, Brazil and Spain.
On Saturday, the World Health Organisation activated stage three of its six-stage global influenza plan. Stage three puts nations on "pandemic alert", urging them to intensify surveillance for unusual outbreaks of influenza-like illness and severe pneumonia, but is less serious than the declaration a pandemic is under way.
- With NZPA, AP
Anyone who has travelled to Mexico or North America in the last fortnight should contact Healthline (0800 611 116) for information. They should seek medical advice if they are displaying flu-like symptoms.
