At least one million people in the United States have had swine flu, or around 50 times more than the number of cases reported to health authorities, an official at the Centers for Disease Control and Prevention (CDC) said Friday.

"We're saying that there have been at least a million cases of the new H1N1 virus so far this year in the United States," Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the CDC told a news briefing.

"Reported cases are really just the tip of the iceberg," she said of the roughly 287,000 confirmed cases of (A)H1N1 flu in the United States.

Around 3,000 people infected with swine flu in the United States have had to be hospitalized and 127 people are reported to have died.

The CDC arrived at its figure of one million cases based on computer models and surveys of communities known to have been hard hit by the new strain of H1N1 flu.

Through community surveys looking at flu-like illness "in areas where we know there's a lot of the strain circulating and in many of those communities, they're reporting proportions of about 6 percent of community members having had an illness that's consistent with the new virus," Schuchat said.

A community survey conducted in New York City, where the CDC believes there have been half a million cases of (A)H1N1, showed 6.9 percent of residents experienced flu-like illness during a three week period in May, Schuchat said.

"From their virologic testing, they knew that most of that influenza-like illness was based on this new H1N1 strain, and from that, they estimated that around half a million New York City residents may have been infected with this new virus… without necessarily seeking care," Schuchat said.

Although an infection rate of around six percent is low compared with seasonal influenza, said Schuchat, "the survey in New York looked at a several-week attack rate while seasonal flu usually happens over weeks to months."

Schuchat said the actual figure of infected people in the United States was probably higher than one million and warned that swine flu might see higher infection rates than seasonal influenza.

"We believe the attack rates of this new virus, particularly in young people, may exceed the kind of attack rates we see with seasonal influenza," said Schuchat.

The highest rates of illness due to (A)H1N1 flu are in people under 25. The median age of people who have been hospitalized for (A)H1N1 flu in the United States is 19, and the median age of those who have died is 37.

Schuchat repeated a warning that the new strain of swine flu could come back in a more virulent form with the return of flu season in the autumn and urged communities to begin mapping out a vaccination campaign.

Five companies are working to develop a vaccine against (A)H1N1 flu, said Schuchat, without naming them.

earlier related report

Second Briton with swine flu dies: govt

A second Briton has died after contracting swine flu, the Scottish government said Sunday.

The 73-year-old man died in hospital in Paisley, central Scotland, late Saturday and had "serious underlying health problems", having been in intensive care for two weeks.

Scotland's Health Secretary Nicola Sturgeon said: "Although it is concerning that the patient had swine flu, we are aware that the patient had very serious underlying health issues.

"It's important to remember that the vast majority of those who have H1N1 are suffering from relatively mild symptoms."

The dead man's identity has not been released. A spokesman for his family said: "Our beloved relative was private in life and we would ask that his privacy continues to be respected".

A total of 4,323 swine flu cases have been diagnosed in Britain.

Earlier this month, another Scot, 38-year-old Jacqueline Fleming, became the first person with swine flu to die outside the Americas. She also had underlying health problems.

Swine flu has infected nearly 60,000 people in 113 countries and killed 263 people since late March, the World Health Organisation said Friday.

Britain showed the second steepest increase after Chile, according to the WHO's figures.

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