Bird flu less deadly, but more widespread, than official numbers suggest

Survey finds 1 to 2 percent infection rate in affected populations

The deadly H5N1 avian influenza virus may not be quite so lethal after all, an analysis of more than 12,000 blood samples suggests.

Since 2003, the World Health Organization has recorded 573 cases of humans infected with bird virus. Of those, 58.6 percent have died, leading to great concern that the virus could cause a devastating pandemic if it adapts to spread easily among humans.

But many more people may have contracted the virus and fought it off with few or no symptoms, suggest Peter Palese, Taia Wang and Michael Parides of Mount Sinai School of Medicine in New York City. The team analyzed other researchers’ data on a total of 12,677 people from seven countries where the virus has been seen and who may have been exposed to the virus.

In general, about 1 to 2 percent of the people carried antibodies against the H5N1 virus, indicating that they had been infected at some point. The rate varied from 0.6 percent to 2.1 percent using World Health Organization criteria for confirming H5N1 cases. Analysis of other studies that didn’t fit those criteria place the infection rate between 0.5 and 3.4 percent. The World Health Organization’s criteria may underestimate the infection rate and may also miss some deaths due to the virus, the researchers report online February 23 in Science.

A higher infection rate than expected isn’t good news, says Philippe Buchy of the Pasteur Institute of Cambodia in Phnom Penh. The more people infected, he says, the more chances the virus has to adapt itself so that it can be passed from person to person.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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