Istanbul, Turkey ? Preliminary tests show that the strain of bird flu virus that has hit at least 15 people in Turkey has evolved in a way that may make it somewhat more hazardous to human beings, although it still lacks the capacity to be passed easily from person to person, international health officials said Wednesday.

The analysis, based on the sequencing of one of the virus’ genes, suggests at least some of the H5N1 bird flu virus here carries a change in one of its proteins that lets it more easily attach to human cells and penetrate them, according to Michael Perdue of the World Health Organization.

“It’s a little concerning because the virus is still trying new things in its evolution,” said Perdue, who is overseeing the agency’s response to the Turkish outbreak from WHO headquarters in Geneva.

Influenza experts are studying the apparent change to determine its significance, Perdue said. A spokesman for Britain’s Medical Research Council, which is involved in the research, said it would take a few days to confirm the preliminary findings.

The experts believe the genetic change may make it easier for the virus to pass from chickens to people. It has not given it the capacity to be easily passed from person to person – a trait the virus would need in order to trigger a global epidemic of bird flu.

Nancy Cox, who heads the influenza branch at the Centers for Disease Control and Prevention, said the change was found in one sample of H5N1 isolated from a Turkish child who recently died of the infection. The hemagglutinin protein, which the virus uses to attach to cells of the respiratory tract, had an alteration not usually seen in avian influenza viruses. The change has been seen in previous outbreaks, in China in 2003 and in Vietnam last year.

Experts from the United Nations Food and Agriculture Organization warned that the virus could become permanently entrenched in Turkey, thereby increasing its risk to people and the chance it could evolve further. “The highly pathogenic avian influenza virus H5N1 could become endemic in Turkey,” the FAO said in a statement.

Two deaths have been attributed to bird flu in Turkey. The fatalities were the first outside of China and Southeast Asia, areas where a total of 78 people have died in the past two years. More than 100 people have been hospitalized in Turkey with flu symptoms.

The virus has spread across 30 out of 81 Turkish provinces, from the far east to the Mediterranean coast, and has sparked a frantic effort to stem the disease by killing off infected poultry.