Swine flu kills US man, spreads to Australia, Japan

A Washington state man with H1N1 influenza died last week, health officials said, the third US sufferer to die as the new flu strain confirmed in more than 2,200 Americans appeared in Japan and Australia.

Health officials have warned that the true number of cases may be underestimated. Although most cases appear to be mild, the new swine flu strain has killed just as seasonal flu does.

Another 48 people have died in Mexico and one each in Canada and Costa Rica.

Washington state officials said on Saturday a man in his 30s with underlying heart conditions died last week, state governor Chris Gregoire describing his death as "a sobering reminder that influenza is serious".

The virus has moved into the southern hemisphere, where influenza season is just beginning, and could mix with circulating seasonal flu viruses or the H5N1 avian influenza virus to create new strains, health officials said.

"One of the big challenges with influenza viruses is the way that they change, the way they combine and their prevalence in a number of species," Anne Schuchat of the US Centres for Disease Control and Prevention told a news briefing on Saturday.

Meanwhile health officials in Britain confirmed seven new cases of the H1N1 flu virus yesterday, bringing the total to 55.

The Health Protection Agency said all seven of the cases were from eastern England.

Two of the new cases are adults who came into contact with previously diagnosed cases.

The remaining five cases in the southeast comprise one adult and four children from the London area, the HPA said.

"These are cases who were swabbed last week and who may have acquired their infection before the closure of their school," it said in a statement.

"Since then, antivirals have been given to all children and staff as a precautionary measure," it said in a statement.

On Saturday health officials said Britain had nine new cases of the virus, eight in England and one in Scotland.

Last week the Department of Health said swine flu was still a threat to the population.

The deadly influenza strain has infected more than 4,000 people worldwide, the World Health Organisation said on Sunday, increasing its count by almost 1,000 a day.