(Agencies/Xinhua)
Updated: 2006-01-10 14:27

Hundreds to thousands of people may be infected with bird flu, but have mild symptoms and do not get admitted to hospital, thereby failing to appear in official figures, Swedish researchers reported Monday.

A survey of 45,478 people in FilaBavi, a Vietnamese demographic surveillance site with confirmed outbreaks of H5N1 in poulty during April to June 2004, found as many as 750 developed flu-like symptoms after contact with sick or dead birds, according to researchers at the Karolinska Institute in Stockholm.

More lab tests should be performed to determine if any of those identified in the survey had contracted bird flu, the researchers said.

"During the widespread Asian highy pathogenic avian influenza (HPAI) epidemic in poultry, the disease has been reportedly rare in humans. Our findings, however, suggest that in populations living in close contact with poultry, in areas endemic for HPAI, transmission to humans may be frequent," the scientists say in a report that appears in the latest edition of the U.S. journal Archives of Internal Medicine.

"The results suggest that the symptoms most often are relatively mild and that close contact is needed for transmission to humans," the researchers conclude.

The new finding adds fuel to an ongoing debate over the true number and severity of human infections with the highly pathogenic H5N1. There have been 146 laboratory-confirmed human cases of H5N1 flu reported to World Health Organization (WHO) as of Jan. 6. with 76 deaths.

Health officials worry the virus may mutate into a form that can spread among people, raising fears of a pandemic. A flu that jumped from birds to humans in 1918 killed as many as 50 million people worldwide.

Vietnam has been struggling with an outbreak of the avian influenza H5N1 strain in poultry since late 2003. Professor Peter Dunnill, an expert on vaccines for avian flu at University College London said rural communities in Vietnam have been living with bird flu for more than 10 years and may have developed resistance to it.

The finding comes as Europe - already on edge over the bird flu scare - is reeling from reports that 15 people in Turkey have been infected with H5N1 influenza, apparently transmitted from poultry, and three children have died.

The latest figures were reported by Turkish authorities; the World Health Organization has so far confirmed only four cases in Turkey, of which two have died.