GENEVA — The human death toll from the deadly H5N1 strain of bird flu reached 103 after five people died from the disease in Azerbaijan, the World Health Organization said Tuesday.

WHO said seven of 11 patients from Azerbaijan had tested positive for H5N1 in samples checked at a major laboratory in Britain. Five of those cases were fatal.

The sources of infection were still under investigation, but officials suspected a connection to the feathers of dead swans.

"The majority of cases have occurred in females between the ages of 15 and 20 years," WHO said. "In this community, the defeathering of birds is a task usually undertaken by adolescent girls and young women."

So far, there was no indication of direct exposure to dead or diseased poultry in some of the cases. That has been the usual source of exposure for humans who caught bird flu.

Health officials fear the virus could mutate into a version that could easily be transmitted between people, potentially triggering a global pandemic.

China agreed to give WHO samples from infected animals following complaints that Beijing was hampering vaccine research by withholding such samples, Dr. Julie Hall, an official of the WHO office in Beijing, said today.