Health authorities in Queensland are checking people who may have had contact with a man who suffered a flu-like illness in Mexico recently.
The state's chief health officer Dr Jeanette Young on Thursday stressed there were no confirmed cases of swine flu, although nine "suspect" cases were being tested.
Dr Young said as a result of increased public awareness, Queensland Health identified a man who had returned a positive blood test for influenza A.
"This individual became sick while in Mexico on April 13 and returned on the 19th," Dr Young said.
"He went to his local emergency department on April 27 as a precaution although he had recovered.
"He was swabbed and because he was no longer experiencing symptoms, a blood sample was also taken to allow extra testing.
"The swab, as expected, was negative for influenza A.
"The blood test showed suspected influenza A.
"This means he may have had this virus at some stage in the past."
Dr Young said the case did not meet the nationally agreed definition of swine flu.
"Because we are taking every precaution, Queensland Health is currently checking to make sure his close contacts have not had any illness," she said.
"We are also seeking further advice from the commonwealth today as to the need for any further action."
Meanwhile authorities in Queensland have tracked down the last two passengers who shared a flight with New Zealand schoolchildren who contracted swine flu.
They have been given antiviral medicine and are undergoing tests.
All seven Queensland passengers from the Air New Zealand flight, which was later found to have had on board three students who tested positive for swine flu, have now been located.
"All have been given Tamiflu and there's no indication there's any problem with any of them," a Department of Health spokesman told AAP.
Dr Young said while there had yet to be a
confirmed case in Australia, flu clinics would be established and schools would be closed in any community where there was an outbreak.
Health Minister Paul Lucas said the number of people being checked and cleared was changing by the hour.
Specialist nurses have been stationed at Brisbane, Gold Coast and Cairns international airports to assess at-risk people.
Hand-held scanners that can detect high body temperatures were in place at the airports and being turned on during Thursday evening.
New customs declaration forms identifying sick passengers were also being rolled out.
"You'll be breaching federal law if you make a false declaration," Mr Lucas said.
"This is a notifiable disease in Queensland - if someone has it and has tested positive then they must notify Queensland Health."
Queensland Health Director-General Mick Reid, who visited the state's north on Thursday, said the threat should not be underestimated.
"We've had avian flu with us for six years and in that six years people have contracted that flu from birds, but there has been no reported instance of human-to-human avian flu contact," he said.
"We've had swine flu for six weeks and in that six weeks we've had it extending from pigs to humans and now from human-to-human."
Airport checks were stepped up as the World Health Organisation (WHO) raised its flu alert level to phase five out of six, signalling that a pandemic was "imminent".
Premier Anna Bligh has cancelled a trade trip to the Middle East and Europe so she can coordinate Queensland's swine flu response.
"With the upgrading by the WHO to phase five, my priority is ensuring we are doing everything possible to prepare for this growing threat and to be a part of the national planning," Ms Bligh said.