As the bird flu death toll rises in China, the American medical community isn't panicking — at least not yet.
There is, however, much caution and uncertainty as doctors from around the world monitor the H7N9 virus that has claimed at least six lives in China, where state-run media confirmed the 21st case Sunday.
Although it has not developed the potentially catastrophic ability to spread from human to human — authorities think it jumps only from infected fowl to people — the strain, along with its true nature and the speed of its mutation, remains a mystery.
Another key unanswered question is how quickly a vaccine can be produced.
"Anybody who thinks they can prognosticate about what's going to happen hasn't been in the influenza field for very long," said Dr. Gregory A. Poland, a medical professor and director of the Vaccine Research Group at the Mayo Clinic. "This thing could fade into obscurity, or it could further mutate. ... This is enough to make us sit up straight and pay lots of attention, not to the point of alarm yet, but it's very early."
While Americans have little cause for concern, the situation is different in China.
Shanghai and two other major Chinese cities have shuttered their live poultry markets in an attempt to slow the spread of the virus. Late last week, more than 20,000 chickens, ducks, geese and pigeons were slaughtered after the virus was found in pigeon samples from local markets, the Chinese news agency Xinhua reported.
Unlike viruses such as the H5N1 flu strain that has killed hundreds over the past 15 years, H7N9 doesn't cause obvious symptoms in birds, making it much more difficult to track. It also appears to be more lethal than the H1N1 swine flu virus that swept across the U.S. four years ago.
But it has been difficult to get a handle on the danger of H7N9, and it will take time to find out.
"There's so few cases that we don't really have a good idea of the overall severity. It's possible, of course, that only the most severe cases are being picked up and being diagnosed," said Dr. Nancy J. Cox, director of the influenza division at the Centers for Disease Control and Prevention. Dr. Cox also heads the CDC's World Health Organization Collaborating Center for Surveillance, Epidemiology and Control of Influenza.
The openness of the Chinese government, or the lack thereof, could further complicate the situation, some health professionals say.
Beijing has come under criticism in the past from international health officials for its unwillingness to share data on public health challenges that originate inside China.
Dr. Cox stressed that Chinese authorities appear to be sharing all relevant information about the H7N9 virus and the suspected number of cases.
But the Chinese government may become less forthright if the situation worsens and could choke off the flow of medical information shared among nations, he said.
"We've got first-rate labs, and China does, too. But we're not constrained politically or socially from communicating the science in any way. They are," Dr. Poland said. "That's what gives you pause and hesitation. Their hesitation on SARS cost hundreds of lives."
A decade ago, Chinese authorities repeatedly said that the SARS epidemic — short for severe acute respiratory syndrome — was under control, despite strong evidence to the contrary.
As it spread, Chinese doctors began to accuse their own government of covering up just how widespread the outbreak had become.
That doesn't seem to the case with H7N9, Dr. Cox said.
"Our feeling is that we have a really good sense of what's going on over there in terms of the cases," she said. "They're working very, very quickly."
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