H1N1 ‘swine’ flu has infected an estimated 1 million in U.S.

At least 1 million Americans have contracted the novel H1N1 influenza, according to mathematical models prepared by the Centers for Disease Control and Prevention, while data from the field indicate that the virus continues to spread even though the normal flu season is over, and that an increasing proportion of victims are being hospitalized.

Meanwhile, the virus is continuing its rapid spread through the Southern Hemisphere.

Nearly 28,000 laboratory-confirmed U.S. cases of the virus, also known as swine flu, have been reported to the CDC, almost half of the more than 56,000 cases globally reported to the World Health Organization.

But Lyn Finelli, a CDC flu surveillance official, told a vaccine advisory committee meeting in Atlanta on Thursday that standard models of viral spread indicated that many times that number had been infected. Although 1 million may seem like a high number, between 15 million and 60 million Americans are infected by the influenza virus during a normal flu season.

At least 3,065 of those infected with this flu in the U.S. have been hospitalized, and 127 have died. The very young are most likely to be infected, Finelli said, but older patients seem to suffer more: Though the average age of those infected is 12, hospitalized patients are on average 20 years old, and the average age of those who die is 37.

The normal seasonal flu virus has virtually disappeared from this country, as expected. But the novel H1N1 virus is continuing to spread, and now accounts for 98% of all cases.

“It doesn’t look like transmission is declining at all,” Finelli said.

The spread is highest in New England and the Northeast. “Very high volumes” of patients have overwhelmed hospitals and labs in New York’s Monroe County -- which includes Rochester -- according to Dr. Andrew Doniger, county public health director. He called on those who have mild symptoms to self-medicate at home.

In the Southern Hemisphere, which is one month into its flu season, several countries, particularly Chile, Argentina and Australia, are already feeling the effects of the new virus. Chile has had more than 4,000 lab-confirmed cases and seven deaths, Argentina more than 1,200 cases and 17 deaths, and Australia 3,200 cases and three deaths.

In Argentina, the virus is spreading particularly rapidly in the conurbano, the densely populated working-class suburbs and slums that ring Buenos Aires. Area hospitals are postponing elective surgeries to free more beds for flu patients, and the government is sending mobile clinics into many neighborhoods.

In Chile, ER visits have tripled and waiting times in public hospitals are seven hours or more.

Epidemiologists fear that the novel H1N1 virus may exchange genetic information with other flu viruses while it is working its way through the Southern Hemisphere, and develop a greater pathogenicity when it returns to the north this fall, but so far that is not happening, said WHO Director-General Margaret Chan.

In a news conference in Moscow on Thursday, she said that “the virus is still very stable. . . . But we all know the influenza virus is highly unpredictable and has great potential for mutation.”

One surprising victim of the virus is a pig in Argentina. Jorge Amaya, director of the animal health and sanitation service there, said that the animal had recovered and that other pigs were being tested for the virus. He said he thinks the pig caught it from a human.

That was the initial theory when researchers found the virus in a Canadian herd early in the pandemic, but tests showed that it was different from the one that had infected their caretaker. No one knows how the pigs became infected.

The U.S. Department of Agriculture has been monitoring pigs throughout this country for signs of the virus, but has reported no infections.

Some help for the upcoming winter flu season is on the way. The French pharmaceutical company Sanofi-Aventis said Thursday that it had begun large-scale production of a vaccine against the novel H1N1 virus. It did not say how many doses it was preparing, and noted that it was still producing seasonal flu vaccine for the Northern and Southern hemispheres.

The company has the capacity to make 270 million doses of vaccine a year at its three plants, two in the United States and one in France. The novel H1N1 vaccine has to be tested before it can be used.

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thomas.maugh@latimes.com