Australian health officials on Friday revealed the country's first case of swine flu resistant to antiviral drug Tamiflu, but insisted the public was not at risk.
West Australian (WA) authorities said a 38-year-old Perth man initially responded to the drug but relapsed when the resistant strain developed and is now in critical condition.
Chief health officer Tarun Weeramanthri said the case was rare and isolated, and did not pose a risk to the public.
"There is no evidence that the virus has spread to other people, none of the patient's family or hospital staff caring for him have contracted the virus, and he has not been in contact with the wider community," he said.
"Experience from overseas shows us that these cases tend to be confined to individual patients and it is not uncommon for it to occur in people who have weakened immune systems."
WA Health said there have been 13 reported cases of Tamiflu-resistant swine flu around the world.
Australia, now emerging from the southern hemisphere winter, has been hard-hit by swine flu with 169 related deaths among nearly 36,000 cases.
The government has ordered 20 million shots, nearly one per person, of an under-development flu vaccine which is expected to be available by October.