Australia reports four new cases of swine flu

The three boys, aged 9, 10 and 12, tested positive to the H1N1 virus on Wednesday, a week after they returned from a family holiday in Los Angeles.

The youngest boy was the first identified with the virus.

The latest cases raise the overall number of confirmed infections to five

Health authorities immediately rushed to contain any spread of the virus, quarantining the boy, his family and 26 classmates at Clifton Hill Primary school in Melbourne's inner north.

All are being treated with anti-viral drugs Tamiflu and Relenza. Later on Wednesday, Victorian Health Minister Daniel Andrews announced the boy's older brothers also have the illness but are at home because they are not ill enough to require hospital treatment.

Victoria's chief health officer, Dr Rosemary Lester, said the 10-year-old's Grade 5 class would now also be quarantined and treated with anti-viral drugs.

But the 12-year-old, who attends a secondary college in Melbourne's north, "has not been at school long enough during his infectious stage" to warrant quarantine or anti-viral medication for his classmates.

Parents of students at the secondary school should consult their GP if they are concerned about their children's health, while Department of Human Services officers would be on hand at school to offer more information.

Confirmation of the new cases came after NSW Health Minister John Della Bosca said a NSW woman had also been infected with the potentially deadly H1N1 virus while travelling in the US earlier this month.

The woman has recovered from the illness, and was not considered to be infectious when she returned to Australia last week. There have now been five reported cases of swine flu in Australia.

The country's first case of swine flu was a 28-year-old NSW woman who flew into Brisbane from Los Angeles on May 7.

In the Victorian case, the schoolboy was diagnosed with swine flu after being taken to his GP on Tuesday with symptoms.

Dr Lester said the boy would have been contagious when he was at school on Monday and up to seven days afterwards.

The boy has been quarantined at home with his family, who have shown symptoms and are undergoing tests.

His grade three classmates, a teacher and teacher's aide will be quarantined at home for five days and authorities are working to contact anyone else who may have come into close contact with the boy.

"They're (the families) being level-headed and sensible about it, but of course they are concerned as you would expect," Clifton Hill Primary School principal Geoff Warren said.

Kathryn O'Connell, whose eight-year-old son Josh is in the nine-year-old's class, said the school had reacted well.

"It is mildly alarming, but everything that the school can do is being done so we are not overly concerned," Ms O'Connell said.

"Obviously, we've heard and read a lot about the worldwide flu scare. (I'm) not sure how much is a media beat-up but I believe the school and the authorities are doing all they can at the moment."

Dr Lester said there was "virtually no chance" any fellow passengers were infected because the boy flew home six days before he became sick.

However, passengers sitting close to the family on flight QF94 from Los Angeles to Melbourne on May 12 will be contacted and urged to look out for symptoms.

Federal Health Minister Nicola Roxon said there was still no "live" transmission of the virus in Australia, but added the situation could develop very quickly.

"I need to reiterate to the community that we are very well placed to deal with any outbreak of swine flu here in Australia," she said.

Prime Minister Kevin Rudd said Ms Roxon and the nation's chief medical officer had warned some weeks ago that given the global nature of the outbreak, Australia could expect cases.

"The question practically for the health authorities is to deal with it efficiently, competently," he told reporters in Perth.