Influenza becoming deadlier as U.S. population grows older

Death rate doubled in '90s over that in 1970s and '80s


WASHINGTON - The flu has turned much deadlier in the United States over the past decade because the nation is getting older and the virus may be getting bolder.

The influenza virus killed an average of 36,155 people per year in the 1990s, compared with 20,000 a year over the two previous decades, according to a new study by the federal Centers for Disease Control and Prevention published today in The Journal of the American Medical Association.

In the 1970s and 1980s, flu was so mild that it killed fewer than 5,600 people in three separate years. But between fall 1992 and spring 1999, annual flu deaths never dropped below 27,000 and reached a high of 51,296 in the 1997-1998 season. Experts said the 1999-2000 season was probably worse, but final statistics aren't yet available.

Flu seemed to tail off in 2000-2001 and seemed mild in 2001-2002, CDC officials said, citing preliminary data. It's still too early to tell for the 2002-2003 season because February is the traditional peak, but deaths are a bit below average so far. Nonetheless, the long-range trend remains troubling.

"These data indicate that the magnitude of the problem is larger than we once thought," said CDC director Dr. Julie Gerberding.

Flu and pneumonia, lumped together for statistical purposes, are the No. 7 cause of death in America, after heart disease, cancer, stroke, chronic lung diseases, accidents and diabetes. It is the No. 4 cause of death for people 85 and older.

The number of Americans 85 and older doubled from 1976 to 1999. That means "we have a large group of people growing more vulnerable" to flu, said CDC flu expert and study co-author Dr. Keiji Fukuda.

As people age, their weakened immune systems make them more vulnerable to flu and respiratory syncytial virus or RSV, an unrelated virus that causes flu-like symptoms. Once thought to be mostly an infant illness, RSV kills an average of 11,321 people a year - 78 percent of them over 65.

Ninety percent of the people who died from flu in the 1990s were 65 or older.

Another factor is growth of a strain of influenza called A(H3N2) that is far deadlier than others. That strain was responsible for 80 percent of flu deaths in the 1990s. It reached epidemic levels four straight years, from fall 1996 to spring 2000, "a very unusual occurrence," said Dr. W. Paul Glezen, an epidemiologist for the Influenza Research Center at Baylor College of Medicine in Houston. Before that, only once had a particular flu strain struck big two years in a row, he said.

Doctors still don't know why A(H3N2) ran rampant in the 1990s, but Glezen suspected that the strain might have mutated a bit to counter natural immunity and vaccinations. Fukuda disagreed, saying he doesn't think the flu is any more virulent than in the past.

CDC recommends flu vaccinations for anyone 65 or older, as well as anyone with chronic medical conditions such as heart disease, lung problems, or diabetes. While two-thirds of the elderly get vaccinated, only about one-third of younger people at risk get the shots.

CDC also encourages shots for people between 50 and 64 and children ages 6 months to 23 months. It's not too late to get vaccinated for this season, Fukuda said.

There is no vaccine for RSV, a virus that seems able to strike people repeatedly, said Dr. Larry Anderson, a CDC expert.

As bad as flu was in the 1990s, it will likely get much worse, the CDC predicts. A 1999 CDC study said a pandemic of flu that spreads fast, far and fatally is inevitable. A similar pandemic killed more than 20 million people worldwide in 1918. If one of the same virulence strikes again, it would likely kill up to 207,000 Americans, send up to 734,000 people to the hospital and cost the U.S. economy up to $167 billion, the CDC estimates.

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