A new strain of influenza that comes from chickens may mutate into a bug that can be spread from person to person, a change that could lead to a worldwide epidemic, an expert says.

"There is no evidence yet of human-to-human transmission, but the very nature of this virus means it will acquire that property," said Robert G. Webster, a member of the World Health Organization's influenza team. "It is only a matter of time."Other experts don't agree.

Webster, a virus expert at the St. Jude Children's Research Hospital in Memphis, Tenn., said Monday that six people - all in Hong Kong - have been confirmed as infected with the new flu strain, called H5N1. All are thought to have contracted the disease from live chickens. Two patients died, but one death is linked to complications of treatment and not to the disease itself.

A 2-year-old boy recovered from the flu after being hospitalized in November, and three more people remain hospitalized.

On Tuesday health officials in Hong Kong said two young cousins of the boy apparently have contracted the disease.

Hong Kong announced new measures to monitor and contain the outbreak, including flu alert broadcasts, a flu hot line and tighter policing of the import, marketing and preparation of poultry.

H5N1 is the first flu strain known to be transmitted to humans from birds. Webster said the human immune system is defenseless against the virus. If the virus mutates so that it can be transmitted between people, it could rage around the globe, he said.

Flu shots now in use offer no protection, but Webster said an anti-viral drug called amantadine is effective against the new flu.

Webster, just returned from Hong Kong, said there is no indication that H5N1 has moved beyond Hong Kong.

Government officials there said Monday that a large wholesale poultry market was closed and will not reopen until Thursday. Vendors at the Cheung Sha Wan Poultry, which sells more than one-third of the 80,000 chickens imported into Hong Kong daily from China, asked for a cleanup to restore public confidence in poultry - even though no infected chickens have been found there.