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 yesterday 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," Dr Anne Schuchat of the US Centers for Disease Control and Prevention told a news briefing yesterday.
"This is why it is so important for countries to have a strong capacity to deal with influenza and also why it is very important to understand what happens at the interface between people and animals."
Before the Washington man's death was announced, the CDC reported 2,254 confirmed US cases of the virus with 104 people in hospital, up from 1,639 cases previously.
"Today there are almost 3,000 probable and confirmed cases here in the United States," Schuchat said. "The good news is we are not seeing a rise above the epidemic threshold."
Japan reported four cases, and globally officials reported more than 4,200 people in 30 countries had been ill. Australia reported its first case, a woman who been travelling in the United States but officials said she had made full recovery.
"We think this virus is in most of the United States," Schuchat said. "The individual numbers are likely to be a very great underestimate."
More Americans are seeing doctors for influenza-like illnesses at a time of year when such visits usually decline.
Schuchat said tests showed they do not all have the new H1N1 virus. Many have seasonal flu - the H1N1 seasonal strain, the H3N2 seasonal strain and influenza B - and other infections.
Seasonal flu kills 250,000 to 500,000 people globally and infects up to a third of the population each year.
Health experts have not openly criticised efforts by other countries to stop the virus from getting in - most notably China and its territory of Hong Kong, which have quarantined travellers in contact with patients.
A spokeswoman in Hong Kong said yesterday that a Mexican traveller confirmed as Hong Kong's first and only case of the new flu strain had been discharged from hospital.
The unidentified man, who unwittingly caused the confinement of almost 300 guests and staff at a Hong Kong hotel where he had stayed, had been in hospital for a week.
China put seven people who had been exposed to three Japanese passengers diagnosed with the H1N1 flu in quarantine, the official Xinhua news agency quoted the government as saying.
Mexican health ministry spokesman Carlos Olmos said the government was testing thousands of samples to confirm which patients with severe respiratory symptoms were actually infected with the flu.
He said more than 5,000 tests had been done on suspected cases and that 1,578 people were ill but were being treated.
After the virus was identified on April 23rd, Mexico banned public events and shut schools, bars, restaurants and many businesses to prevent people from gathering. Officials say disinfection of public spaces has helped control its spread.
Schools in the capital will reopen tomorrow.
But the state government of Jalisco, home to Mexico's second-largest city Guadalajara, said schools, nightclubs and theatres there will remain shut for another week after three suspected flu deaths.
Ms Schuchat said it is not yet clear whether some measures taken have slowed the outbreak, but she said it was clear that early detection methods had alerted the world quickly.
She noted that the AIDS virus, which has now killed 25 million people globally and infects 33 million, spread for years before it was even identified.
"If we end up having a bad pandemic of influenza from this strain we would have had a real jump-start on things like vaccines," she said.
Reuters