Australia on Saturday reported its first case of swine flu, after a woman tested positive for the disease as she returned from a trip to the United States, the government said.
"We have a person who had contracted the disease overseas and has fully recovered by the time they returned to Australia," Health Minister Nicola Roxon said.
"This person identified themselves to a border nurse... to explain that she had been ill. It is understood that the person contracted and recovered from the disease while overseas and recovered by the time she flew back into Australia."
As a precaution, Roxon said authorities were contacting other passengers who were on the 28-year-old's flight from Los Angeles, which arrived in Australia on Thursday.
The woman was likely no longer infectious when she was in transit and had tested "weakly" positive, with the flu strain detected at a very low count, Roxon said.
It had been more than a week since the woman was first ill and she was not displaying any symptoms, but presented herself to medical staff at Brisbane airport for a swab, Roxon said.
She had been travelling through the US by herself and began experiencing "typical flu-like symptoms" on April 27, said Jeanette Young, Queensland state's chief health officer.
"She has fully recovered and the experts believe that she was not infectious on that flight travelling from LA through to Brisbane," Young said.
A total of 567 Australians have been tested for the disease, and 18 are awaiting results, Roxon said, adding that despite the confirmed case, the government has decided not to elevate its pandemic threat level to the containment phase.
"This is clearly a serious development but we are in a situation where the best medical advice seems to be indicating that this person would not have been infectious," she said.
"Because at this stage there is no evidence of any live infection in Australia the advice currently is for us not to change that alert level."
Mexico has been at the epicentre of the global A(H1N1) flu epidemic, with most deaths recorded there, but the United States on Friday became the country with the highest number of patients, confirming 1,639 cases in 43 states.
The World Health Organization (WHO) meanwhile said that 2,500 people in 26 countries had tested positive for the virus.