More ill with Avian flu than first thought

Avian flu, which killed almost 60 percent of those known to be infected, actually struck many more people worldwide but didn't make them very sick, a new analysis finds.

The actual fatality rate of the H5N1 flu strain is probably less than 60 percent, considering that millions of people may have been infected over the past eight years, the researchers report.

The analysis results confirm earlier findings, said one expert, Dr. Marc Siegel, an associate professor of medicine at New York University. It's still not clear how fatal the strain actually is, but the research "emphasizes that H5N1 is not as deadly in humans as is being proposed by some people," said Siegel, author of "Bird Flu: Everything You Need to Know About the Next Pandemic." Siegel added that he doesn't think "this particular virus is going to mutate to go easily from human to human. That's extremely unlikely."

Scientists and public health officials have been sounding the alarm for years about the potential that the avian flu strain called H5N1 could become a major threat to humans. As of last December, the World Health Organization reported a total of 573 cases since 2003; of those, 59 percent were fatal.

In the new report, researchers from Mount Sinai School of Medicine in Manhattan launched a combined analysis of 20 studies that examined blood test results from more than 12,500 people. They found that 1 percent to 2 percent of them had signs that they'd been infected with H5N1. Most of those said they hadn't recently had cold or fever symptoms.

The research suggests that few people are being infected by the strain, Siegel said.

The analysis appears in the Feb. 23 online issue of Science.