State of Denial; The bird flu has long stalked China's mainland, and its human toll is only beginning to come to light.

Byline: Melinda Liu and Alexandra A. Seno, With Sarah Schafer in Shanghai

Late last year, when many experts were bracing for a resurgence of the SARS virus, Klaus Stohr's thoughts were elsewhere. The head of the World Health Organization's global influenza program was worrying about the bird flu. Trained as a veterinarian, Stohr had long been fascinated by diseases that could make the leap from animals to humans. One such killer bug--the H5N1 avian-flu virus--had killed six of 18 infected people in Hong Kong in 1997. And last fall it was back.

A series of apparently unrelated outbreaks of avian flu had erupted among birds in Vietnam, South Korea and Japan. Then, while attending a medical conference in Okinawa in October, Stohr learned of a possible human death from the flu in China's teeming Guangdong province. Genetic sequencing confirmed that a girl had succumbed to H5N1 in late February 2003--back before SARS sparked a regionwide panic. "Now the H5N1 virus has killed again," Stohr remembers thinking. "A new pandemic could be just a matter of time."

The Guangdong case was never reported in the press, and as recently as last week Chinese officials categorically denied any mainland deaths due to avian flu. What might have been a medical footnote, though, has taken on grim new importance. As of last Friday, 18 people in Vietnam and Thailand had succumbed to the flu, and mass poultry culling and vaccinations were underway in 10 Asian countries. The great fear now is that the virus will mutate into a form that can spread among humans, possibly through genetic mixing with an existing human-flu bug. And China's massive population offers hundreds of millions of chances for H5N1 to do so.

An unpleasant truth is only now coming to light, largely against Beijing's wishes: H5N1 has stalked China for a long time. Before mainland academics and journalists were ordered not to discuss the subject last week, scholars at Huanan Agricultural University in Guangzhou reported that the H5N1 virus had appeared widely in poultry throughout Guangdong, Fujian, Guangxi, Shandong and other provinces as far back as 2001. "I suspect fatal outbreaks such as that in Hong Kong in 1997 have happened many times before in China," says Kennedy Shortridge, an influenza expert formerly of Hong Kong University. "Fifteen years ago children were dying from unexplained illnesses," but awareness of the disease was in short supply back then, he says. Even now many doctors don't suspect bird flu in many cases. "When someone dies of H5N1, the first test just shows death due to influenza A," says bioengineer Henry Niman of Harvard Medical School. "It's a virus you don't find unless you're looking for it."

And that's something Beijing has been reluctant and unprepared to do. After nearly a week of playing hide-and-seek with the media, Chinese officials last week acknowledged "weaknesses and vulnerability in the [country's] animal-disease surveillance system." Since late January, China has owned up to the presence of bird-flu infections in 13 of 31 provinces. But Beijing's stubborn refusal to admit any human deaths due ...