U.S. public health officials watching bird flu outbreak in China

• New bird flu strain in China isn%27t a threat in U.S.%2C health officials say
• All the Chinese cases appear to be in people exposed to live poultry
• U.S. public health systems are working on a vaccine in case it mutates

U.S. health officials are developing laboratory strains of China's new bird flu so they can make vaccines quickly if necessary.

The move is in response to a new bird flu that has emerged in China in the past two months. So far, it is confined to that nation.

Bird flu has killed six of the 21 people who've gotten it, a mortality rate that keeps public health officials up at night. The strain, named H7N9, appears to be transmitted from poultry.

This week,Chinese officials began slaughtering more than 20,000 birds in a Shanghai poultry market to help stop the spread of the strain, which has been found in four provinces along China's eastern seaboard.

Chinese health officials are monitoring more than 530 people who had been in close contact with confirmed cases, the World Health Organization reported.

The United States has not issued any travel advisories for China but for a decade has advised Americans traveling to China to avoid contact with birds and other animals.

The Centers for Disease Control and Prevention is on the case, said CDC director Thomas Frieden.

"We work to have the public's back," Frieden said. "It's our job to be concerned and to move quickly whenever there's a potential problem."

But the public doesn't need to worry, he said. "There's no evidence that the virus is being transmitted between people or that it's present in the United States."

Public health officials are engaged in aggressive surveillance, said William Schaffner, an influenza expert who chairs Vanderbilt University's department of preventive medicine in Nashville. Any out-of-the ordinary pneumonia cases in the United States are being looked at carefully and specimens sent to ultra-fast specialty labs, and the results are communicated quickly to federal health officials, Schaffner said.

The good news is that compared with the severe acute respiratory syndrome (SARS) outbreak in 2003, China has made huge changes to how it responds to this kind of outbreak, Schaffner said.

"Ten years ago, China was very secretive and the world's health community was frustrated," he said. "This time around, China is being very open and aggressive in dealing with the outbreak."

The H7N9 bird flu in China is of concern because it's a new strain that hasn't been seen in humans before, said Joseph Bresee, chief of the CDC's epidemiology and prevention branch, influenza division. However, so far it seems the only way to get it is to be in close contact with sick poultry.

Chinese health officials quickly developed a test for exposure to the virus, then took blood samples from more than 100 people who'd had close physical contact with the first three people who got the flu strain. None of them had any evidence of immunological response, meaning their bodies hadn't been exposed to it.

"With influenza you'd expect at least 20% to 30% of family members to develop illness," said Frieden. "So that's good news."

Bird flu strains regularly emerge in southeast Asia, where there are large poultry flocks. Every few years, one appears that humans can get, but usually only by coming into contact with sick birds. Health officials worry when a strain emerges that can pass easily from human to human.

That hasn't happened in this case, health officials emphasize.

At least, it hasn't happened yet, Schaffner said. Flu viruses are notoriously changeable; virologists talk about their "constant genetic turbulence." That's why "we have to watch this outbreak like a hawk, because if it does mutate, we could have a worldwide flu pandemic on our hands," he said.

To be on the safe side, health officials and vaccine manufactures are creating the strains now, Frieden said. "It would only be produced if there was evidence of widespread human-to-human transmission," he said.

The U.S. effort began "within a matter of days" of the first word of the new variant, Schaffner said.

While the news out of China might sound scary, the global response is immensely reassuring, he said.

"The average person should say 'Wow. This is an international, integrated public health prevention structure that's really working!' Schaffner said. "This is exactly how the international community ought to work."