Japan and Hong Kong reported on Friday that they have each found a patient with the type of swine flu that has proven resistance to Tamiflu - days after Denmark reported the first such case.
In Japan, a strain of swine flu resistant to Tamiflu, the leading pharmaceutical defence against the virus, was found in a patient in western Osaka in mid-May, said Health Ministry official Takeshi Enami.
He said the strain developed in a Japanese patient who was on the drug to prevent the illness, and it has not spread to others. The patient, whose age and gender were not released, has since recovered after taking Relenza - another effective influenza drug.
In Hong Kong, a Tamiflu-resistant strain of swine flu was found in a sample taken from a 16-year-old girl who tested positive to the flu upon her arrival from San Francisco last month, the territory's Department of Health said Friday.
She has since recovered without taking Tamiflu or Relenza. The virus, however, showed sensitivity to Relenza.
Scientists have been worried that the new swine flu could swap genes with seasonal or other types of flu and perhaps mutate into a more dangerous or more infectious form.
But Enami said genetic tests on the virus from the Japanese patient found no trace of such crossing.
Experts plan to conduct further tests on the virus at the National Institute of Infectious Diseases in Tokyo.
"We do not see it as an immediate threat to public health as long as the Tamiflu-resistant strain is not spreading from person to person," Enami said.
Until an effective vaccine is developed, the drugs Tamiflu and Relenza are considered the best available defence against the swine flu virus.
According to the latest report Wednesday from the UN's World Health Organisation, there have been 77,201 swine flu cases worldwide, and 332 deaths.
The WHO report said seven of those deaths have been in Australia, three in Thailand and one in the Philippines.
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