The World Health Organization says China and Singapore have joined the list of countries that have reported Tamiflu-resistant swine flu viruses.

Charles Penn, a scientist with the Geneva-based agency, says the WHO has also been alerted informally to the discovery of a small number of other Tamiflu-resistant viruses but he won't say where they were found.

The WHO has received formal notification of seven cases of Tamiflu resistance among people with the pandemic flu - three from Japan and one each from Canada, Denmark, Hong Kong and Singapore.

Chinese authorities haven't yet filed a formal report including information about its case but alerted the WHO of the initial laboratory finding through the Global Influenza Surveillance Network.

Penn says to date there is no evidence that Tamiflu-resistant viruses are spreading.

He says all the reported cases to date have been isolated, with no connections among them and no sign that the infected people passed resistant viruses to their contacts.

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