Epidemic experts say they are investigating the apparent spread of Tamiflu-resistant swine flu virus among four patients at Duke University Medical Center in Durham, N.C., and five in a hospital in Wales.

These clusters appear to be the first in which a virus resistant to the antiviral Tamiflu, a mainstay of flu treat, has spread from person to person, researchers said Friday. If Tamiflu-resistant virus spreads widely, swine flu will become tougher to treat and may cost more lives, says Duke's Daniel Sexton, who is leading the hospital's investigation.

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