Laboratory tests have confirmed that a 22-year old woman in Nigeria died from the virulent H5N1 strain of bird flu last month, the World Health Organisation said.

"The initial positive test findings from a laboratory in Nigeria were confirmed by the WHO Collaborating Centre for Reference and Research on influenza in London," the WHO said in a statement on its website.

The WHO said samples from all contacts of the woman, who died in the Nigerian city of Lagos on January 17, had tested negative and did not show any sign of transmission of bird flu among humans.

"Further investigations are under way to identify the source of the infection," the statement said.
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